Open Access

Potential Candidate Genes for Improving Rice Disease Resistance

  • Amandine Delteil1,
  • Jie Zhang2,
  • Philippe Lessard3 and
  • Jean-Benoit Morel1Email author
Rice20103:9035

https://doi.org/10.1007/s12284-009-9035-x

Received: 8 September 2009

Accepted: 20 December 2009

Published: 16 January 2010

Abstract

Diseases caused by fungal and bacterial pathogens like Magnaporthe oryzae and Xanthomonas oryzae pv. oryzae are responsible for considerable yield loss. Up to now, in rice, the modification of the expression of more than 60 genes from diverse origins has shown beneficial effects with respect to disease resistance. In this paper, we review this large set of data to identify the best genes and strategies to achieve disease resistance by transgenic approaches. Altered expression of genes involved in signal transduction and transcription may lead to many unwanted side effects, like lesion mimic phenotypes. Moreover, modification of resistance to abiotic stress has been neglected and should be carefully examined in the future. Genes like resistance genes and pathogenesis-related genes can confer broad spectrum and high levels of resistance to several pathogens. Preformed expression of defense is often observed but does not necessarily lead to detrimental effects. Although examples of gene pyramiding are scarce, they suggest that this is a very promising strategy. More field evaluation of the transgenic plants is required to draw final conclusions on the usefulness of these genes for improving disease resistance.

Keywords

RiceTransgenic plantDisease resistance

Introduction

To meet the increasing demand on the world food supply, we will have to produce up to 40% more rice by 2030 (Khush 2005). This will have to be on a reduced sowing area due to urbanization and increasing environmental pollution. For example, the sowing area in China decreased by eight million hectares between 1996 and 2007 (China Statistical Bureau; http://www.stats.gov.cn/english/statisticaldata/yearlydata/). Improvement of yield per plant is not the only way to achieve this goal; reduction of losses by biotic and abiotic stress is also a solution. According to FAO estimates, diseases, insects, and weeds cause as much as 25% yield losses annually in cereal crops (Khush 2005). In particular, fungal diseases can cause important losses (between 1% and 10%) regionally (Savary et al. 2000). In China alone, it is estimated that one million hectares are lost annually because of blast disease (Khush et al. 2009).

Fungal and bacterial pathogens represent a permanent threat on rice cultivation. Between 1987 and 1996, fungicides represented up to 20% and 30% of the culture costs in China ($46 million) and Japan ($461 million) respectively, whereas they represent approximately 10% of the costs in Europe and the USA (http://beta.irri.org/solutions/). Thus, a strong effort has been invested in improving disease resistance. These efforts could now benefit from the knowledge gained on mechanisms underlying disease resistance.

Since the initial definition of the plant resistance (R) genes by Flor (1942), many R genes have been identified. The vast majority of the known R genes is composed of proteins carrying nucleotide-binding sites and leucine-rich repeat motifs (NBS-LRR; Jones and Dangl 2006). Most R genes recognize pathogen effectors developed by pathogens to inhibit defense, although there are a few exceptions (e.g., Lee et al. 2009). Some of these effectors thus correspond to the initial definition by Flor of the avirulence gene. Depending on the presence/absence of these R genes and of the matching avirulence product, the interaction will be incompatible (plant is resistant) or compatible (plant is susceptible).

Many R genes have been identified in rice and most code for NBS-LRR genes (Ballini et al. 2008; White and Yang 2009). After recognition mediated by the R gene, signal transduction occurs and requires regulators such as MAP kinases (Mishra et al. 2006). Finally, transcription factors like WKRYs activate a deep transcriptional reprogramming of the cell (Eulgem 2005), leading to the activation of defense responses per se. These include production of antimicrobial secondary metabolites (phytoalexins like momilactones in rice; Peters 2006), pathogenesis-related (PR) proteins (e.g., chitinases, glucanases, PBZ1 in rice; Jwa et al. 2006; van Loon et al. 2006), cell wall strengthening (Hückelhoven 2007), and programmed cell death, leading to hypersensitive response (HR; Greenberg and Yao 2004). The genes that act downstream of the disease resistance pathway are collectively called defense genes.

Most of the elements involved (receptors, regulators, transcription factors, and defense genes) are well conserved across species. For example, the NPR1 gene is a central regulator in both monocots and dicots. The NPR1 gene was successfully used in several plant species like Arabidopsis (Cao et al. 1998), rice (Chern et al. 2001), tomato (Ekengren et al. 2003), and wheat (Makandar et al. 2006). Similarly, the mlo gene functions in barley (Peterhänsel and Lahaye 2005), tomato (Bai et al. 2008), and Arabidopsis (Consonni et al. 2006). These observations are critical for biotechnology approaches since they suggest that one gene from one species can provide an interesting trait in another.

Preformed defense systems likely play a role in basal resistance in limiting the growth of a normally virulent pathogen. Preformed or constitutive defense systems involve cuticle (Skamnioti and Gurr 2007) and cell wall (Juge 2006) strengthening. In rice, like in other plants, silicon accumulation plays direct and indirect roles in basal resistance (Ma and Yamaji 2006). Antimicrobial molecules, called phytoanticipins, can also accumulate before infection (Morrissey and Osbourn 1999). Increasing information from Arabidopsis and other plants indicates that the overproduction of PR proteins confers resistance, that mutations in regulator genes negatively regulating disease resistance can increase defense gene expression (e.g. Noutoshi et al. 2005; Petersen et al. 2000), or that over-expression of regulator genes acting positively on disease resistance can increase defense gene expression (Hammond-Kosack and Parker 2003).

More than 60 genes have now been over-expressed or mutated in rice for fundamental or applied research. Molecular and biological studies of these transgenic plants allow a better understanding of signaling pathways, cross talks, and pathogen specificities. These experiments lead to the putative disease resistance pathway shown in Fig. 1. This figure illustrates that genes in the three major steps of the disease resistance pathway are known in rice, opening the possibility to assess the usefulness of each category of gene.
Fig. 1

Position in the putative disease resistance signaling pathway of the rice genes that were used in plants to improve disease resistance. The genes listed here are the ones for which the demonstration of usefulness was made in planta. Details on these genes are provided in Table 1.The position of the OsDR8, OsDR10, pi21, spl18, and OsSBP genes is not shown. This schematic view illustrates the three steps leading to pathogen resistance: recognition via general (e.g., OsWAK1) and specific receptors (Pi and Xa genes), signal transduction, transcription, and defense response, involving pathogenesis-related genes and cell death. The OsPLDβ, OsFAD7/FAD8, and OsAOS2 genes are involved in the jasmonic acid pathway and OsSSI2 in the salicylic acid pathway. The OsLOL2, OsLSD1, OsSpl11, and OsSpl7genes are negative regulators of cell death, and mutants for these genes display spontaneous lesions resembling disease.

Rice stable transformation via Agrobacterium tumefaciens has become a routine technique in laboratories (Toki et al. 2006). Nowadays, even if japonica is frequently used because it is highly amenable to transformation, indica transformation efficiency has sufficiently improved to allow its use in functional validation experiments and field trials in the appropriate environments.

A tool kit for breeders for marker-assisted selection was recently described (Ballini et al. 2009). Here, we extensively review the cases of improvement of disease resistance by over-expression of transgenes. Rice blast caused by the fungus Magnaporthe oryzae and bacterial blight caused by Xanthomonas oryzae pv. oryzae are the most serious and widespread diseases in rice production. Therefore, we focused this paper on these two pathogens. We did not review the abundant literature on strategies to increase insect resistance (see for example Ye et al. 2009 and references therein). We provide guidelines for selecting transgenic strategies for fungal and bacterial disease improvement, for selecting genes, and analyzing their effects. General elements on the different possible strategies to improve disease resistance in plants were previously described (Campbell et al. 2002) and are not presented here.

Rice genes improving disease resistance

Sixty rice genes for which improvement of disease resistance was shown are presented in Tables 1, 2, 3, and 4. We selected a gene only if the corresponding paper provided data concerning in vivo resistance and some information on the spectrum of pathogens that were tested. These genes were separated into three major groups: 41 rice genes (Table 1 is a selection of 24 the most characteristic genes, the remaining genes are in Electronic supplementary materials (ESM), Supplemental Table 2), five genes from plants other than rice (Table 2), and nine genes from organisms that are not plants (Table 3). Finally, we also review five cases of gene pyramiding (Table 4). Figure 1 provides a few examples of where the rice genes are likely acting. Although the genes tested were not all precisely positioned on the disease resistance pathway, they can be tentatively attributed to four major steps in this pathway: recognition, signaling, transcription, and defense response.
Table 1

Rice Genes Potentially Useful for Improving Rice Disease Resistance

Gene

Transgenic plant

Disease reduction

Isolate tested

Enhanced defense expression

Side effects

References

Accession

QTL

Name

Annotation

Type

Genotype

Japonica/Indica

Expression

Type

M. oryzae

X. oryzae pv oryzae

Other pathogens or pes

M. oryzae

X. oryzae pv oryzae

Before infection

After infection

OsBRR1

LRR-RLK

Receptor

Nipponbare

Japonica

Constitutive

OX

80%

nd

nd

3

nd

nd

nd

None

Peng et al. 2009

Os03g12730

Yes

Pi9

NBS-LRR

Receptor

TP309

Japonica

From own promoter

OX

Yes

nd

nd

21

nd

nd

nd

nd

Qu et al. 2006

Os06g17920

Yes

OsWAK1

Protein kinase

Receptor

Aichiasahi

Japonica

Constitutive

OX

50%

nd

nd

nd

nd

nd

nd

None

Li et al. 2009

Os11g46900

Yes

OsMAPK5a /BIMK1/OsMP K5

MAP kinase

Signaling

Nipponbare

Japonica

Constitutive

RNAi

85%

nd

85% (Burkholderia glumae )

nd

nd

+

nd

Susceptible to abiotic stress

Xiong and Yang 2003; Song and Goodman 2002

Os03g17700

Yes

OsSpl11

U-bOX/Armadillo Repeat Protein Endowed with E3 Ubiquitin Ligase activity

Signaling

IR64

Indica

Constitutive

KO

90%

85%

nd

10

4

+

nd

Lesion mimic

Zeng et al. 2004; Yin et al. 2000

Os12g38210

Yes

OsPLD β 1

Phospholipase D

Signaling

Nipponbare

Japonica

Constitutive

RNAi

90%

70%

nd

nd

nd

+

nd

Lesion mimic

Yamaguchi et al. 2009

Os10g38060

Yes

OsSSI2

Steroyl Acyl Carrier FA Desaturase

Signaling

Nipponbare

Japonica

Constitutive

RNAi and KO

95%

90%

nd

nd

nd

+

nd

Lesion mimic

Jiang et al. 2009

Os01g69080

Yes

OsRac1

rac-like GTP-binding protein 2

Signaling

Kinmaze

Japonica

Constitutive

Active form

20%

46%

nd

nd

nd

+

+

Lesion mimic

Kawasaki et al. 1999; Ono et al. 2001; Thao et al. 2007

Os01g12900

Yes

NH1

Regulatory protein

Signaling

TP309

Japonica

Constitutive

OX

No effect

95%

Susceptibility to white-backed planthopper

nd

nd

+

nd

Lesion mimic

Yuan et al. 2007; Chern et al. 2005

Os01g09800

Yes

OsAOS2

ALLENE OXIDE SYNTHASE (P450 74A2)

signaling

Nipponbare

Japonica

Inducible

OX

85%

nd

nd

nd

nd

+

+

nd

Mei et al. 2006

Os03g12500

Yes

OsGH3.1

Indole-3-acetic acid-amido synthetase

signaling

Bomba

Japonica

Constitutive

OX

51%

nd

nd

nd

nd

+

nd

Reduced height

Domingo et al. 2009

Os01g57610

Yes

OsGAP1

GTPase-activating protein

signaling

Aichi asahi

Japonica

Constitutive

OX

nd

55%

nd

nd

3

+

nd

nd

Cheung et al. 2008

Os02g22130

Yes

OsDR8

Thiazole biosynthetic enzyme 1-1

signaling

Minghui63

Indica

Constitutive

RNAi

Yes

350% increase

nd

nd

nd

-

-

nd

Wang et al. 2006

Os07g34570

no

OsWRKY13

WRKY TF protein

TF

Minghui63

Indica

Constitutive

OX

Yes

Yes

nd

nd

nd

+

nd

Susceptible to abiotic stress

Qiu et al. 2007; Qiu et al. 2009a, b;

Os01g54600

Yes

OsWRKY31

WRKY TF protein

TF

Zhonghua 17

Japonica

Constitutive

OX

67%

nd

nd

nd

nd

+

nd

Root growth affected

Zhang et al. 2008

Os06g30860

Yes

OsWRKY45

WRKY TF protein

TF

Nipponbare

Japonica

Constitutive

OX

100%

nd

nd

nd

nd

+

nd

Reduced height

Shimono et al. 2007

Os05g25770

Yes

OsWRKY71

WRKY TF protein

TF

Nipponbare

Japonica

Constitutive

OX

nd

71%

nd

nd

nd

+

nd

nd

Liu et al. 2007

Os02g08440

Yes

OsWRKY53

WRKY TF protein

TF

Nipponbare

Japonica

Constitutive

OX

Yes

nd

nd

nd

nd

+

nd

None

Chujo et al. 2007

Os05g27730

Yes

OsNAC6

NAC domain-containing protein 48

TF

Nipponbare

Japonica

Constitutive and stress-inducible

OX

Yes

nd

nd

nd

nd

nd

nd

Reduced height/improved abiotic resistance

Nakashima et al. 2007

Os01g66120

Yes

RBBI2-3

Serine proteinase inhibitor

PR

TP309

Japonica

Constitutive

OX

100%

nd

nd

5

nd

nd

nd

None

Qu et al. 2003

Os01g03360

Yes

GNS1

1,3;1,4-beta glucanase

PR

Nipponbare

Japonica

Constitutive

OX

Yes

nd

nd

nd

nd

+

+

Lesion mimic

Nishizawa et al. 2003

Os05g31140

Yes

OsDR10

Unknown

other

Minghui63

indica

Constitutive

RNAi

nd

95%

nd

nd

+

+

+

None

Xiao et al. 2009

Os08g05960

Yes

pi21

Proline-rich protein

other

Aichiasahi

Japonica

Constitutive

RNAi

90%

no effect

nd

10

na

No change

nd

None

Fukuoka et al. 2009

Os04g32850

Yes

OsSBP

Selenium-binding protein homologue

other

Kinmaze

Japonica

Constitutive

OX

50%

50%

nd

nd

nd

+

+

nd

Sawada et al. 2004

Os01g68770

Yes

OX over-expresser, KO knockout mutant

Table 2

Plant (Non-rice) Genes Potentially Useful for Improving Rice Disease Resistance

Gene

Transgenic plant

Disease reduction

Isolate tested

Enhanced defense expression

Side effects

References

Name

Annotation

Origin

Type

Genotype

Japonica/Indica

Expression

Type

M. oryzae

X. oryzae pv oryzae

Other pathogens or pest

M. oryzae

X. oryzae pv oryzae

Before infection

After infection

Rxo1

NBS-LRR

Maize

Receptor

Kitaake

Japonica

Constitutive

OX

nd

nd

X. oryzae pv oryzicola

nd

nd

nd

nd

nd

Zhao et al. 2005

AtNRP1

Transcription

Arabidopsis thaliana

Signaling

TP309

Japonica

Constitutive

OX

86%

Yes

increased susceptibility to RYMV

nd

nd

+

+

Lesion mimic susceptible to abiotic stress

Fitzgerald et al. 2004; Quilis et al. 2008

Dm-AMP1

Defensin

Dahlia merckii

PR

Pusa Basmati 1

Indica

Constitutive

OX

45%

nd

68% (R. solani )

nd

nd

no change

no change

nd

Jha et al. 2009

PRms

PR protein

Zea mays

PR

Senia

Japonica

Constitutive

OX

95%

nd

F. verticillioides, H. oryzae and E. chrysanthemi

nd

nd

+

+

nd

Gomez-Ariza et al. 2007

Rs-AFP2

defensin

Raphanus sativus

PR

Pusa Basmati 1

Indica

Constitutive

OX

77%

nd

45% (R. solani )

nd

nd

No change

No change

None

Jha et al. 2009

OX over-expresser, KO knockout mutant

Table 3

Non-plant Genes Potentially Useful for Improving Rice Disease Resistance

Gene

transgenic plant

Disease reduction

Isolate tested

Enhanced defense expression

Side effects

References

Name

Annotation

Origin

Function

Genotype

Japonica/Indica

Expression

Type

M. oryzae

X. oryzae pv oryzae

Other pathogens or pest

M. oryzae

X. oryzae pv oryzae

Before infection

After infection

Cecropin A

Cecropin A

Hyalophora cecropia

Antimicrobial

Senia

Japonica

Constitutive

OX

87%

nd

nd

nd

nd

No change

No change

Fertility affected

Coca et al. 2006

AFP

Antifungal

Aspergillus giganteus

Antimicrobial

Senia

Japonica

Constitutive

OX

45%

nd

nd

nd

nd

nd

nd

None

Coca et al. 2004

cht42

Endochitinase

Trichoderma virens

Antimicrobial

Pusa Basmati1

Indica

Constitutive

OX

nd

nd

62% (R. solani )

nd

nd

nd

nd

None

Shah et al. 2009

ChiC

Family 19 chitinase

Streptomyces griseus

Antimicrobial

Nipponbare

Japonica

Constitutive

OX

85%

nd

nd

nd

nd

nd

nd

None

Itoh et al. 2003

lactoferrin

Lactoferrin

Human

Antimicrobial

nd

nd

Constitutive

OX

No effect

No effect

Burkholderia (Pseudomonas) plantarii

nd

nd

nd

nd

nd

Takase et al. 2005

hrf1

Hairpins (protein elicitor)

Xanthomonas oryzae pv. oryzae

Elicitor

R109

Japonica

Constitutive

OX

56%

nd

nd

nd

nd

+

nd

None

Shao et al. 2008

avrXa27

Transcription factor

Xanthomonas oryzae pv. oryzae

Elicitor

Nipponbare

Japonica

Inducible

OX

No effect

38%

35% (Xoc ), no effect on E. chrysanthemi

nd

nd

+

nd

Delay of Flowering and early senescene

Tian and Yin 2009

flagellin

Flagellin

Acidovorax Avenae

Elicitor

Koshihikari

Japonica

Constitutive

OX

Yes

nd

nd

nd

nd

+

nd

Lesion mimic

Takakura et al. 2008

pemG1

Unknown

Magnaporthe grisea

Elicitor

Nipponbare

Japonica

Constitutive

OX

35%

nd

nd

nd

nd

+

nd

nd

Qiu et al. 2009a, b

OX over-expresser, KO knockout mutant

Table 4

Pyramiding for Improving Rice Disease Resistance

Gene

Transgenic plant

Disease reduction

Isolate tested

Enhanced defense expression

Side effects

References

Name

Annotation

Origin

Function

Genotype

Japonica/Indica

Expression

Type

M. oryzae

X. oryzae pv oryzae

Other pathogens or pest

M. oryzae

X. oryzae pv oryzae

Before infection

After infection

tlp, chi, Xa21

Thaumatin-like protein, chitinase and Receptor like kinase

Oryza sativa

PR and receptor

ASD16, ADT38, IR72, IR64,White Ponni,

Indica

Constitutive

OX

nd

90%

95% (R. solani )

nd

nd

nd

nd

nd

Maruthasalam et al. 2007

Xa21, chi, Bt

Receptor like kinase, Chitinase and Bt toxin

Oryza sativa and Bacillus thriengensis

PR and receptor

IR72

Indica

Constitutive

OX

nd

90%

63% (R. solani ) and yellow stem borer

nd

nd

nd

nd

None

Datta et al. 2002

RCH10, RAC22, Glc, RIP

RCH10 (basic chitinase), RAC22 (acidic chitinase), β-Glucanase and BRibosome Inactivating protein

Oryza sativa

PR

9311

Indica

Constitutive

OX

Yes

nd

60-100% reduction of kernel smut (T. barclayana ); also resistance to U. virens

nd

nd

nd

nd

None

Zhu et al. 2007

RIP, chi

Ribosome inactivating protein and chitinase

Oryza sativa and Maize

PR

Kenfong

nd

Constitutive

OX

no effect

nd

25% (R. solani ), no effect on B. oryzae

nd

nd

nd

nd

nd

Kim et al. 2003

PINA, PINB

Structural proteins

Triticum aestivum

other

M202

Japonica

Constitutive

OX

53%

nd

22% (R. solani )

nd

nd

nd

nd

nd

Krishnamurthy et al. 2001

OX over-expresser, KO knockout mutant

Major resistance genes for Xanthomonas resistance (Xa genes) and blast resistance (Pi genes) were recently reviewed by White and Yang (2009) and Ballini et al (2008), respectively. We selected only a few examples (Pi9 and Xa21) to illustrate the use of these R genes in transgenics. Other genes coding for receptor-like proteins likely involved in basal resistance such as OsWAK1 and OsBRR1 were also included in our study. These two genes may have broad-spectrum effects since at least for blast disease, they were not identified as major resistance genes.

Genes with a role in signaling and transcription factors represent the majority of the cases (30 out of 41 genes) found in the literature. Although most of the transgenics built in these reports were initially obtained for fundamental research, they also provide information on their potential for protecting plants from disease. Eight of these genes (SPL11, XB15, OsPLDB1, OsRac1, SPL18, PACK1, OsGAP1, and OsDR8) were originally found in rice, whereas the other genes were found by homology to genes in other models (ex NH1 in Arabidopsis and OsPti1 in tomato).

Out of the nine transcription factors identified in the literature, six are WRKYs. Their detailed effects on disease resistance were recently reviewed (Pandey and Somssich 2009). WRKYs are also known to be involved in abiotic stress response and development. The challenge in using WRKY genes in transgenic is to identify genes that have a positive effect on resistance and no or little detrimental effects on abiotic stress and/or development.

Although 14 PR protein families are known in rice (Van Loon et al. 2006), only PR genes from a few families have been over-expressed.

Other plant genes improving rice disease resistance

A few genes from plants other than rice have been tested in rice (Table 2). Not surprisingly, the central regulatory gene NPR1 (Cao et al. 1998) belongs to this group of genes. Three PR genes are also found, suggesting a good potential for this large category of genes. However, more than 50 genes have now been identified in different plant species as regulating disease resistance (Hammond-Kosack and Parker 2003). Although some of these genes may not work in rice for biological reasons, the important conservation of the disease resistance pathways between plants should allow transfer from one plant to another. There is therefore a large potential in this category of genes.

Transferring one gene from one species to another may lead to unexpected effects. This was the case when the Arabidopsis NPR1gene was transferred to rice (Fitzgerald et al. 2004). The rice plants over-expressing AtNPR1 also displayed an environmentally regulated and heritable lesion mimic phenotype (see below).

Moreover, a recent report on OsWRKY45 demonstrates that over-expressing (in japonica rice) a japonica allele of the gene confers increased susceptibility to bacterial blight, whereas over-expressing an indica allele of the gene confers increased resistance to bacterial blight. In contrast, both alleles conferred increased resistance to blast disease (Tao et al. 2009). This finding suggests that one should be careful when transferring one gene from one background to another, even within the Oryza sativa species.

Non-plant genes improving rice disease resistance

Table 3 summarizes available data on non-plant genes. Two types of genes were used. One group of genes is represented by proteins having known antimicrobial effects. Most of the genes reported are from fungi, one is an insect gene (Cecropin A), and one a human gene (lactoferrin). Side effects could be expected in these cases. For example, Cecropin A is a known anticancer molecule (Mader and Hoskin 2006). Moreover, the acceptance of plants for human food containing a human protein is likely to be very low.

A second group of genes like avirulence genes are known to activate plant defense responses. In this case, one expects that constitutive or inducible activation of defenses will increase disease resistance. When avirulence genes are used (e.g., avrXa27), pathogen-specific effects are expected. For this reason, most of the cases deal with avirulence genes that are broadly distributed (e.g., flagellin).

There is also a risk that such plants may show unwanted effects because such genes have a strong potential in inducing defense responses. For this reason, it is recommended to use pathogen-inducible promoters. However, such promoters are often either leaky or controlled by developmental signals (Van Loon et al. 2006). Thus, the genes that activate plant defense responses are unlikely to be a good strategy to increase disease resistance.

We excluded from this review 19 rice genes for several reasons (ESM, Supplemental Table 1). First, we excluded genes that have only been tested in heterologous systems. Second, we did not include rice genes for which only negative effects on disease resistance were reported in rice. This is for example the case of the over-expression of the OsMT2b gene that confers enhanced susceptibility to blast (Wong et al. 2004). Finally, there were genes that had only been tested in rice cell cultures but not in entire rice plants. There is thus no in planta demonstration of the usefulness of these genes. These genes should be tested by stable transformation in rice.

Disease protection quantitative effects

Where possible, we quantitatively evaluated the level of resistance. The increase of resistance was measured as the percentage of disease reduction as compared to the presented wild-type controls. It is noteworthy that in most cases, the best control was missing. This control consists in the nullizygous plant, i.e., a non-transgenic sibling originating from a hemizygous plant. In most cases, the control shown is a transformed plant with the empty vector. Since rice transformation induces many somaclonal mutations, such a control is inappropriate. In other cases (e.g., NH1; Chern et al. 2001), several transgenics are presented, highlighting the fact that different insertion events can show large differences. Moreover, the disease protection values were obtained from data obtained on a few plants. Only field evaluation in natural conditions could give a real idea of the effectiveness of these genes. With these caveats in mind, effects smaller than 50% should be considered as weak. For bacterial blight disease, the same criterion was always used (length of lesions), whereas for blast disease resistance, many criteria were used (lesion number, diseased area, etc.). In all cases, the value presented is the most favorable.

Independently of the pathogen, the majority of the reported cases show disease reduction higher than 50%. For blast, two genes (RBBI2-3 and WRKY45; Table 1) showed the best effects with a complete absence of symptoms. Disease reduction higher than 90% was obtained with four other rice genes (Table 1) and the PRm gene from maize (Table 2).

For bacterial blight, the best levels of resistance (higher than 95% reduction of disease) were achieved with two rice genes (OsDR10 and NH1; Table 1) and with two cases of pyramiding (Table 4).

For sheath blight caused by Rhizoctonia solani, the best level was achieved with pyramiding three genes (thaumatin-like protein, chitinase, and Xa21; Table 4). In this case, the data also indicate that this strong effect is only due to the combined action of the thaumatin-like and chitinase proteins, independently of the Xa21 gene (Maruthasalam et al. 2007). Some excellent levels of protection were also shown for kernel smut (caused by Tilletia barclayana; Zhu et al. 2007) by pyramiding (Table 4).

Pyramiding was a good strategy to increase quantitative effects of individual transgenes. For example, while the single chitinase and thaumatin-like genes each conferred about 80% increase of resistance toward sheath blight, the combination of the two genes showed a reduction of 95% of disease.

These different examples of gene pyramiding clearly demonstrate that it is a good strategy to quantitatively improve resistance. From the quantitative point of view, it is noteworthy that all categories of genes (except R genes) provide, on average, the same levels of resistance.

Disease protection qualitative effects

As pathogen populations are quite complex, it is important to have an evaluation of the spectrum of action of the tested genes. Unfortunately, this information is lacking in most cases. For 27/60 genes, only one isolate of one pathogen was tested. Clear information on the spectrum of resistance was provided for only 11 genes. For blast resistance, nine genes were shown to provide resistance to more than one isolate, including RBBI2-3 and Pi21 that also show elevated quantitative effects (Table 1). For blight resistance, five genes showed relatively broad-spectrum resistance, including OsDR10 plants that have high levels of resistance. The SPL11 gene was the only one for which broad-spectrum resistance was shown against both pathogens. However, these plants suffer from strong developmental side effects (see below).

There are 15 genes for which both blast and blight disease resistance have been evaluated (Tables 1, 2, and 3). All genes protecting against blast, except the pi21 gene, were shown to also confer resistance to blight. This is a very promising observation showing that the genes used for one pathogen can be used for another. It is noteworthy that the NH1 gene, a key disease pathway regulator, does not seem efficient against blast disease, whereas it confers good levels against blight (Chern et al. 2005; Yuan et al. 2007).

Quite surprisingly, the expression of the avrXa27 gene, in the presence of the Xa27 gene, did not confer resistance to blast. This may be due to the lack of induction of the avrXa27 gene under the control of the inducible PR1 promoter. However, the PR1 gene is known to be induced by M. oryzae (Mitsuhara et al. 2008). Alternatively, it is likely that the events triggered by the Xa27 gene are not efficient against M. oryzae.

There is so far no report of simultaneous improvement of resistance against blast, blight, and sheath blight diseases. This may be simply due to the absence of data rather than to biological reasons since there are genes conferring enhanced resistance to all combinations of two of these pathogens.

Expression of defense in transgenics

For some plant genes encoding proteins involved in disease resistance (Tables 1 and 2) and encoding avirulence products (Table 3), one can expect perturbation of the events downstream of the pathway, like PR gene expression and phytoalexin production. These perturbations can occur either before and/or after infection. Defense gene expression, often using the PR1 and PBZ1 genes as markers, was evaluated for a large number of cases (37/55).

Elevated defense gene expression before infection was found in 80% of the cases, and these levels could be extremely high. For example, PBZ1 and a peroxidase gene were found to be expressed 40 times higher in over-expressor plants as compared to wild type in the case of the WRKY53 gene (Chujo et al. 2007). Some upstream signaling events were measured in a few cases. The signaling molecule jasmonic acid was found to be less present in plants over-expressing the WRKY13 gene (Qiu et al. 2007). Similarly, reactive oxygen species were detected in several cases (e. g., OsPLDβ1, Yamaguchi et al. 2009; flagellin, Takakura et al. 2008). In one puzzling case, OsDR8, many PRs were down-regulated before (and after) infection, although the plants showed slightly enhanced resistance to blast and a strong increase of susceptibility to bacterial blight (Wang et al. 2006; Table 1). Available micro-array data on over-expressor plants further indicate that defense responses are often widely constitutively over-expressed. For example, 84 genes annotated as responsive to abiotic stress are up-regulated in plants over-expressing OsGH3.1 (Domingo et al. 2009). Similarly, more than 430 genes involved in secondary metabolite synthesis are up-regulated in plants over-expressing OsWRKY13, leading to increased production of the phytoalexin momilactone (Qiu et al. 2009a, b).

An enhanced defense response after infection was observed in eight cases. This was rather expected for most of them since they encode positive regulators of defense. This was less expected for the GNS1 gene (Nishizawa et al. 2003) since this gene encodes a classical glucanase. It is possible that enhanced degradation of the cell wall of M. oryzae by the additional glucanase activity led to the release of molecules that in turn over-induced the defense system. No change of defense induction was observed for five genes (Cecropin A, Dm-AMP1, rTGA2.1, OsMPK6 and Rs-AFP2; Tables 1, 2, and 3) in spite of increased resistance.

Side effects

For 19 cases, there was no specific mention of side effects. No major visible side effects were clearly found for 13 genes. It is noteworthy that for six of these 32 genes for which there are likely little or no visible side effects (OsAOS2, Rack1, OsWRKY71, OsWRKY53, OsGAP1, and OsSBP; Table 1), enhanced defense expression before infection was measured. This suggests that it is possible to increase preformed defense and disease resistance with no obvious side effect. This seems particularly clear for the plants over-expressing OsWRKY53 (Chujo et al. 2007). In this case, more than 200 genes are up-regulated as indicated by micro-array analysis, and one third of these genes, besides genes related to defense, are related to metabolism, transport, proteolysis, and signal transduction.

However, there are 28 cases for which detrimental side effects were reported. Side effects were found with all kinds of genes except receptor genes, although this may be due to an absence of data. Genes involved in signaling and transcription factors appeared to display frequent secondary effects, with 82% and 70% of the observed cases, respectively. Although the number of reported cases is scarce, avirulence genes also produced secondary effects (Table 3).

There were eight rice genes (OsMPK6, OsPti1, XB15, OsPLDβ1, OsSSI2, OsRac1, NH1, and GNS1; Table 1) and one bacterial gene (flagellin; Table 3) where an unexpected lesion mimic phenotype was observed. Lesion mimic plants are well known for their enhanced resistance (Lorrain et al. 2003), such as the spl7, spl11, and spl18 rice mutants (Table 1). This enhanced resistance often correlates with constitutive expression of defense genes (Lorrain et al. 2003). This is also true for the 11 cases found here showing a lesion mimic phenotype, as constitutive expression of defense markers was found. Thus, in these cases, it is likely that constitutive activation of defense pathway(s) leads to the uncontrolled and constitutive triggering of cell death. Pathogen-inducible over-expression of these genes could reduce this side effect while maintaining high levels of resistance after pathogen infection.

Developmental phenotypes were also often observed (13 cases). In many cases, the plants showed a reduced height that often correlated with enhanced expression of PR genes before infection (Tables 1 and 2). For the genes that are well known to be involved in plant development, increase of disease resistance may in fact be a side effect. This may be true for the GH3.1 and GH3.8 genes that both affect auxin metabolism. In the case of WRKY31, a root phenotype was found (Zhang et al. 2008), further indicating that some side effects may have been missed when looking at aerial parts of the plant only.

Micro-array data are available for five genes (OsPLDβ1, OsSSI2, OsGH3.1, OsWRKY13, and OsNAC6; Table 1), providing further information on the molecular events that are modified in the corresponding plants. In Osssi2 knockout plants, almost 300 genes are up-regulated, among which a large set of genes related to metabolism (71), transcription factors (32), kinases (28), and defense (16; Jiang et al. 2009). Quite surprisingly, plants over-expressing the WRKY13 gene, besides over-expressing genes of the flavonoid pathway, also displayed up-regulation of a large set of genes involved in amino acid (475 genes) and nitrogen (162) metabolism (Qiu et al. 2009a, b). Thus, despite this major transcriptional reprogramming, these plants do not seem to have developmental defects (Qiu et al. 2007). In the case of the OsGH3.1 gene, the micro-array data are consistent with the developmental phenotype. Almost 500 genes related to growth and cellular morphology are down-regulated in the plants over-expressing the OsGH3.1 gene (Domingo et al. 2009). Also consistent with the improved tolerance to dehydratation and high-salt concentrations, genes related to response to abiotic stress are differentially regulated in the mutant.

There are four reports for which response to abiotic stress was also indicated. This confirms a well-known observation that biotic and abiotic stresses are strongly connected. There were three genes for which there is an antagonism between disease and abiotic stress resistance (OsMAPK5a, OsWRKY13, and AtNPR1; Table 1). In these cases, the impact on abiotic stress could not be predicted and the gain for disease resistance is counterbalanced with the loss of resistance to abiotic stress. The available data do not clearly indicate whether there are cases where biotic stress resistance is improved without affecting abiotic stress resistance. However, there are several examples (Table 1) where abiotic stress resistance does not seem affected. Thus, at this stage, one should carefully examine effects on abiotic stress resistance when manipulating genes involved in biotic stress resistance.

The complex case of the OsNAC6 gene demonstrates that it will probably be difficult to use this category of genes to improve stress tolerance (Nakashima et al. 2007). Plants constitutively over-expressing OsNAC6 are more resistant to M. oryzae and abiotic stresses but have abnormal plant growth. To try to circumvent this side effect, the OsNAC6 gene was over-expressed under stress-inducible promoters. The resulting plants did not show the initial developmental defect, were resistant to abiotic stress, but were no more resistant to M. oryzae.

Transgene strategies

The vast majority (75%; for details, see Tables 1, 2 and 3 as well as ESM, Supplemental Tables 1 and 2) of the cases of transgenic plants were made in the japonica subspecies. This is a consequence of the fact that japonica rice is easier to transform than the indica type. Nipponbare was the japonica cultivar used in most cases (16 genes), reflecting the fact that this is the original genotype adopted by the rice community for genomic studies.

We only found three examples where inducible promoters were used. In the case of the avirulence gene avrXa27, this was necessary to avoid massive HR cell death triggered by the recognition of the product of the avirulence gene and the corresponding major resistance gene Xa27 (Tian and Yin 2009). In the case of the OsNAC6 transcription factor, this was needed to avoid side effects (growth retardation). Moreover, the permanent activation of some disease signaling pathways caused by the use of a constitutive promoter has a metabolic cost that could be measured in terms of carbohydrate storage losses (see below). In one case of pyramiding, several promoters were used, limiting potential silencing issues (Kim et al. 2003). It is likely that inducible promoters will be required in the future to limit side effects (see below) and yield penalty. Finding such specific promoters is one of the major challenges in this field, and current experiments on whole transcriptome analysis under different biotic and abiotic stresses will provide numerous candidate promoters for cloning.

The vast majority of the favorable effects (46 out of 60) on disease resistance were obtained by over-expressing positive regulators. In the case of the OsRac1 gene, a dominant constitutively active form of the protein was used (Thao et al. 2007). For genes that are negative regulators, two main approaches were taken: silencing using RNAi and insertion mutants. In one case, a dominant negative allele was introduced (rTGA2.1; Fitzgerald et al. 2004).

We only found a few cases (Table 4) of gene pyramiding. The pyramiding was obtained either by crossing individual lines (e.g., Datta et al. 2002) or by co-bombardment of separate transgenes (e.g., Kim et al. 2003). We found no example of several transgenes borne on one single T-DNA, indicating that transferring several transgenes in one single transformation event is not a common strategy.

Finally, it should be noted that the general issues relative to GMOs apply for the plants described in this review. For acceptance of these products, marker-free plants will be required. RNAi plants are also likely to be more easily accepted as no new protein is produced, although co-silencing may also lead to unwanted side effects.

Conclusions and recommendations for future transgenic approaches

Examples of transgenic rice plants expressing genes related to disease resistance have tremendously increased in the past decade. With the publication of the first case of improvement of resistance by over-expressing the Rir1b gene (Schaffrath et al. 2000), more than 60 other cases are now available (Table 1). Besides providing information on the disease regulation networks in rice, they also represent a solid sample of examples for the evaluation of transgenic strategies. The key elements coming from this review are listed in Box 1. Based on the review of these 60 cases, several recommendations can be made.

If examples of gene pyramiding (Table 4) are excluded, this represents the individual examination of the potential of 56 genes (Tables 1, 2, and 3). When excluding genes for which detrimental side effects were observed, only half (28) of the genes remain.

The over-expression or silencing of genes involved in signaling and transcription often leads to negative side effects (e.g., lesion mimics, impaired plant growth; Tables 1, 2, and 3). Thus, one should be careful when using genes involved in signaling and transcription for transgenic strategies.

Alternatively, inducible promoters should be used to reduce the risk and the extent of side effects. This was done, with some success, with the OsNAC6 gene (Nakashima et al. 2007).

Surprisingly, despite the large number of known secreted proteins from pathogens, only a few were used (e.g., pemG1; Table 3). However, pathogen genes coding for avirulence products may not be the best candidates for transgenic approaches as they often trigger secondary effects.

With the example of impaired root development observed for the OsWRKY31 gene (Zhang et al. 2008), one should carefully characterize transgenic plants. An extensive phenotyping with respect to abiotic stress tolerance and development seems to be required to detect subtle side effects. Available data still suggest that it should be possible to improve resistance to biotic stress without negatively affecting abiotic stress resistance.

When applying quantitative requirements for the 28 genes not associated with side effects, a few genes clearly stand out as favorable, depending on the pathogen. For blast disease only, the pi21, PRm, and RBB12-3 genes are amongst the best (disease reduction >90%). For bacterial blight disease only, OsDR10 alone provides more than 95% reduction of symptoms. For sheath blight only, the best gene so far seems to be the Dm-AMP1 gene (Table 1). When applying qualitative and quantitative requirements for the 28 genes without side effects, only a few genes providing resistance to several pathogens can be found. For combined blast and bacterial blight disease resistance, the OsSBP gene is the only one providing increased resistance, although the level of this resistance is rather low (50%). Defensins (Dm-AMP1 and Rs-AFP2) seem to confer good levels of resistance to both blast and sheath blight. These seven genes are amongst the best genes so far for use in transgenic approaches.

R genes and PR genes seem to be a good class of genes to use for transgenic approaches. Plants over-expressing these genes display very little side effects but strong (but likely not durable) protection effects for R genes as well as for PR genes. Thus, very beneficial and straightforward effects will likely be obtained in future transgenic plants over-expressing R genes and PR genes. Defensins seem to have particularly interesting effects (Table 2). While ignored for a long time in rice, defensins seem to exist in rice (Silverstein et al. 2007). Along with the eight classes of PR genes that have not yet been over-expressed in rice, we also suggest using defensins and other small peptides in future transgenic approaches.

It is obvious that missing data limit the possible analysis. It is likely that many genes show protection effects against several pathogens and multiple isolates of one pathogen. One recommendation would be, for the future, that several pathogens and isolates should be tested.

Although we did not review them here, there are several examples of successful improvement of viral resistance by transgenic approach. Expression of the RF2a and RF2b genes provided RTBV resistance (Dai et al. 2008). There are also several cases of improvement of RYMV resistance by a transgenic approach (Pinto et al. 1999; Kouassi et al. 2006). In all these cases, no side effects were observed, indicating that except for potential durability issues, these strategies are efficient.

We identified 13 negative regulators for which a beneficial effect was obtained in knockout plants (Table 1). As in the case of the pi21 gene where good alleles exist in nature, one can expect to find interesting alleles of negative regulators by mutational approaches. With this respect, the Tilling technology (Till et al. 2007) opens the possibility of finding agronomically interesting alleles of negative regulators.

It was previously shown with a limited subset of 35 rice genes involved in disease resistance that these genes tend to co-localize with blast disease quantitative trait loci (QTLs). These genes were found in 72% of the cases in genome areas containing QTLs, and this was significantly different from randomly selected genes (Vergne et al. 2008). In a similar way, the rice genes presented in this updated list of genes involved in disease resistance were tested for co-localization with blast QTLs. For the 41 genes for which favorable disease resistance effects could be produced in transgenic rice (Table 1 and ESM, Supplemental Table 2), 90% were found in blast QTLs. This further supports the idea that disease regulators probably explain many disease resistance QTLs. Thus, the genes of Table 1 and ESM, Supplemental Table 2 can be used as markers for marker-assisted selection.

There are as of yet only a very limited number of examples of gene pyramiding (Table 4). However, these examples are very promising as the corresponding plants show high levels of resistance against several pathogens, and when this was measured, no side effect was observed. Mixed planting of transgenic lines should also be efficient for controlling disease epidemics as shown using wild-type mixtures for blast resistance (Zhu et al. 2000).

It is important to note that the final grain yield has not yet been tested in most cases (e.g., Xa21; Tu et al. 2000). Only two cases of transgenic plants listed here were tested in the field (hrf1plants, Table 3; Xa21, chitinase and Bt toxin plants, Table 4). Although more than 285 GM field trials across the world were performed between 1990 and 2008 (http://www.gmo-compass.org/eng/database/plants/64.rice.html), it is difficult to establish how many assays are planted for rice. Thus, most of the results discussed here need to be validated in the field.

Finally, the question of durability of these transgenic plants needs to be addressed. Resistance in transgenic plants over-expressing R genes is likely to be overcome by the corresponding pathogen. We can make this conclusion based on the many natural situations where newly introgressed R genes did not last more than 1 to 2 years in the case of blast (Correa-Victoria et al. 2004). In contrast, rice plants over-expressing R genes for which the corresponding avirulence product is not highly polymorphic could be more durable, as pathogens are less likely to harbor mutations circumventing recognition. We have no knowledge on the durability of resistance conferred by genes like PR genes and regulators. These genes could be more durable than genes for which the corresponding protein is in close contact with the pathogen. In this case, the development by the pathogen of counter-defense systems could be more difficult. However, the recent finding that many effectors inhibit plant pathogen defense may lead to poor durability of these solutions. Establishing the durability of the transgenic plants resistant to disease represents a major scientific challenge for the coming decades.

Declarations

Acknowledgments

We are thankful to the members of the PYRIZ group for helpful discussions. Amandine Delteil is funded by a PhD grant from the Languedoc-Roussillon district and CIRAD.

Open Access

This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Authors’ Affiliations

(1)
UMR BGPI INRA/CIRAD/SupAgro, Campus International de Baillarguet
(2)
Shanghai LongPing Agricultural Biotechnology Co. Ltd
(3)
Limagrain China

References

  1. Bai Y, Pavan S, Zheng Z, Zappel NF, Reinstädler A, Lotti C, et al. Naturally occurring broad-spectrum powdery mildew resistance in a Central American tomato accession is caused by loss of Mlo function. Mol Plant Microbe Interact. 2008;21(1):30–9.PubMedView ArticleGoogle Scholar
  2. Ballini E, Morel J-B, Droc Gt, Price A, Courtois B, Notteghem J-L, et al. A genome-wide meta-analysis of rice blast resistance genes and quantitative trait loci provides new insights into partial and complete resistance. Mol Plant Microbe Interact. 2008;21(7):859–68.PubMedView ArticleGoogle Scholar
  3. Ballini E, Vergne E, Tharreau D, Nottéghem JL, Morel JB. ARCHIPELAGO: towards bridging the gap between molecular and genetic information in rice blast disease resistance. In: Wang GL, Valent B, editors. Advances in genetics, genomics and control of rice blast disease. Berlin: Springer; 2009. p. 417–25.View ArticleGoogle Scholar
  4. Campbell M, Fitzgerald H, Ronald P. Engineering pathogen resistance in crop plants. Transgenic Res. 2002;11(6):599–613.PubMedView ArticleGoogle Scholar
  5. Cao H, Li X, Dong X. Generation of broad-spectrum disease resistance by overexpression of an essential regulatory gene in systemic acquired resistance. Proc Natl Acad Sci USA. 1998;95(11):6531–6.PubMedView ArticleGoogle Scholar
  6. Chern MS, Fitzgerald HA, Yadav RC, Canlas PE, Dong XN, Ronald PC. Evidence for a disease-resistance pathway in rice similar to the NPR1-mediated signaling pathway in Arabidopsis. Plant J. 2001;27(2):101–13.PubMedView ArticleGoogle Scholar
  7. Chern M, Fitzgerald HA, Canlas PE, Navarre DA, Ronald PC. Overexpression of a rice NPR1 homolog leads to constitutive activation of defense response and hypersensitivity to light. Mol Plant Microbe Interact. 2005;18(6):511–20.PubMedView ArticleGoogle Scholar
  8. Cheung M-Y, Zeng N-Y, Tong S-W, Li W-YF, Xue Y, Zhao K-J, et al. Constitutive expression of a rice GTPase-activating protein induces defense responses. New Phytol. 2008;179(2):530–45.PubMedView ArticleGoogle Scholar
  9. Chujo T, Takai R, Akimoto-Tomiyama C, Ando S, Minami E, Nagamura Y, et al. Involvement of the elicitor-induced gene OsWRKY53 in the expression of defense-related genes in rice. Biochimica et Biophysica Acta (BBA)—Gene Structure and Expression. 2007;1769(7-8):497–505.View ArticleGoogle Scholar
  10. Coca M, Bortolotti C, Rufat M, Peñas G, Eritja R, Tharreau D, et al. Transgenic rice plants expressing the antifungal AFP protein from Aspergillus giganteus show enhanced resistance to the rice blast fungus Magnaporthe grisea. Plant Mol Biol. 2004;54(2):245–59.PubMedView ArticleGoogle Scholar
  11. Coca M, Peñas G, Gómez J, Campo S, Bortolotti C, Messeguer J, et al. Enhanced resistance to the rice blast fungus Magnaporthe grisea conferred by expression of a cecropin A gene in transgenic rice. Planta. 2006;223(3):392–406.PubMedView ArticleGoogle Scholar
  12. Consonni C, Humphry ME, Hartmann HA, Livaja M, Durner J, Westphal L, et al. Conserved requirement for a plant host cell protein in powdery mildew pathogenesis. Nat Genet. 2006;38(6):716–20.PubMedView ArticleGoogle Scholar
  13. Correa-Victoria FJ, Tharreau D, Martinez C, Vales M, Escobar F, Prado G, et al. Studies on the rice blast pathogen, resistance genes, and implications for breeding for durable blast resistance in Colombia. In: Kawasaki S, editor. Rice blast: interaction and control. Dordrecht: Kluwer; 2004. p. 215–27.View ArticleGoogle Scholar
  14. Dai S, Wei X, Alfonso AA, Pei L, Duque UG, Zhang Z, et al. Transgenic rice plants that overexpress transcription factors RF2a and RF2b are tolerant to rice tungro virus replication and disease. Proc Natl Acad Sci USA. 2008;105(52):21012–6.PubMedView ArticleGoogle Scholar
  15. Datta K, Baisakh N, Maung T, Thet KM, Tu J, Datta S. Pyramiding transgenes for multiple resistance in rice against bacterial blight, yellow stem borer and sheath blight. Theor Appl Genet. 2002;106(1):1–8.PubMedGoogle Scholar
  16. Domingo C, Andres F, Tharreau D, Iglesias DJ, Talon M. Constitutive expression of OsGH3.1 reduces auxin content and enhances defense response and resistance to a fungal pathogen in rice. Mol Plant Microbe Interact. 2009;22(2):201–10.PubMedView ArticleGoogle Scholar
  17. Ekengren SK, Liu Y, Schiff M, Dinesh-Kumar SP, Martin GB. Two MAPK cascades, NPR1, and TGA transcription factors play a role in Pto-mediated disease resistance in tomato. Plant J. 2003;36(6):905–17.PubMedView ArticleGoogle Scholar
  18. Eulgem T. Regulation of the Arabidopsis defense transcriptome. Trends Plant Sci. 2005;10(2):71–8.PubMedView ArticleGoogle Scholar
  19. Fitzgerald HA, Chern M-S, Navarre R, Ronald PC. Overexpression of (At)NPR1 in rice leads to a BTH- and environment-induced lesion-mimic/cell death phenotype. Mol Plant Microbe Interact. 2004;17(2):140–51.PubMedView ArticleGoogle Scholar
  20. Flor HH. Inheritance of pathogenicity in Melampsora lini. Phytopathology. 1942;32:653–69.Google Scholar
  21. Fukuoka S, Saka N, Koga H, Ono K, Shimizu T, Ebana K, et al. Loss of function of a proline-containing protein confers durable disease resistance in rice. Science. 2009;325(5943):998–1001.PubMedView ArticleGoogle Scholar
  22. Gomez-Ariza J, Campo S, Rufat M, Estopà M, Messeguer J, Segundo BS, et al. Sucrose-mediated priming of plant defense responses and broad-spectrum disease resistance by overexpression of the maize pathogenesis-related PRms protein in rice plants. Mol Plant Microbe Interact. 2007;20(7):832–42.PubMedView ArticleGoogle Scholar
  23. Greenberg JT, Yao N. The role and regulation of programmed cell death in plant–pathogen interactions. Cell Microbiol. 2004;6(3):201–11.PubMedView ArticleGoogle Scholar
  24. Hückelhoven R. Cell wall associated mechanisms of disease resistance and susceptibility. Annu Rev Phytopathol. 2007;45(1):101–27.PubMedView ArticleGoogle Scholar
  25. Hammond-Kosack KE, Parker JE. Deciphering plant–pathogen communication: fresh perspectives for molecular resistance breeding. Curr Opin Biotechnol. 2003;14(2):177–93.PubMedView ArticleGoogle Scholar
  26. Itoh Y, Takahashi K, Takizawa H, Nikaidou N, Tanaka H, Nishihashi H, et al. Family 19 chitinase of Streptomyces griseus HUT6037 increases plant resistance to the fungal disease. Biosci, Biotechnol Biochem. 2003;67(4):847–55.View ArticleGoogle Scholar
  27. Jha S, Tank H, Prasad B, Chattoo B. Expression of Dm-AMP1 in rice confers resistance to Magnaporthe oryzae and Rhizoctonia solani. Transgenic Res. 2009;18(1):59–69.PubMedView ArticleGoogle Scholar
  28. Jiang CJ, Shimono M, Maeda S, Inoue H, Mori M, Hasegawa M, et al. Suppression of the rice fatty-acid desaturase gene OsSSI2 enhances resistance to blast and leaf blight diseases in rice. Mol Plant Microbe Interact. 2009;22(7):820–9.PubMedView ArticleGoogle Scholar
  29. Jones JDG, Dangl JL. The plant immune system. Nature. 2006;444(7117):323–9.PubMedView ArticleGoogle Scholar
  30. Juge N. Plant protein inhibitors of cell wall degrading enzymes. Trends Plant Sci. 2006;11(7):359–67.PubMedView ArticleGoogle Scholar
  31. Jwa N-S, Agrawal GK, Tamogami S, Yonekura M, Han O, Iwahashi H, et al. Role of defense/stress-related marker genes, proteins and secondary metabolites in defining rice self-defense mechanisms. Plant Physiol Biochem. 2006;44(5–6):261–73.PubMedView ArticleGoogle Scholar
  32. Kawasaki T, Henmi K, Ono E, Hatakeyama S, Iwano M, Satoh H, et al. The small GTP-binding protein Rac is a regulator of cell death in plants. Proc Natl Acad Sci USA. 1999;96(19):10922–6.PubMedView ArticleGoogle Scholar
  33. Khush G. What it will take to feed 5.0 billion rice consumers in 2030. Plant Mol Biol. 2005;59(1):1–6.PubMedView ArticleGoogle Scholar
  34. Khush GS. Jena, KK. Current status and future prospects for research on blast resistance in rice (Oryza sativa L.). In: Wang GL, Valent B, editors. Advances in genetics, genomics and control of rice blast disease. Berlin: Springer; 2009. p. 1–10.View ArticleGoogle Scholar
  35. Kim J-K, Jang I-C, Wu R, Zuo W-N, Boston RS, Lee Y-H, et al. Co-expression of a modified maize ribosome-inactivating protein and a rice basic chitinase gene in transgenic rice plants confers enhanced resistance to sheath blight. Transgenic Res. 2003;12(4):475–84.PubMedView ArticleGoogle Scholar
  36. Kouassi NK, Chen L, Siré C, Bangratz-Reyser M, Beachy RN, Fauquet CM, et al. Expression of rice yellow mottle virus coat protein enhances virus infection in transgenic plants. Arch Virol. 2006;151(11):2111–22.PubMedView ArticleGoogle Scholar
  37. Krishnamurthy K, Balconi C, Sherwood JE, Giroux MJ. Wheat puroindolines enhance fungal disease resistance in transgenic rice. Mol Plant Microbe Interact. 2001;14(10):1255–60.PubMedView ArticleGoogle Scholar
  38. Lee SW, Han SW, Sririyanum M, Park CJ, Seo YS, Ronald PC. A type I-secreted, sulfated peptide triggers XA21-mediated innate immunity. Science. 2009;326(5954):850–3.PubMedView ArticleGoogle Scholar
  39. Li H, Zhou SY, Zhao WS, Su SC, Peng YL. A novel wall-associated receptor-like protein kinase gene, OsWAK1, plays important roles in rice blast disease resistance. Plant Mol Biol. 2009;69(3):337–46.PubMedView ArticleGoogle Scholar
  40. Liu XQ, Bai XQ, Wang XJ, Chu CC. OsWRKY71, a rice transcription factor, is involved in rice defense response. J Plant Physiol. 2007;164(8):969–79.PubMedView ArticleGoogle Scholar
  41. Lorrain S, Vailleau F, Balagué C, Roby D. Lesion mimic mutants: keys for deciphering cell death and defense pathways in plants? Trends Plant Sci. 2003;8(6):263–71.PubMedView ArticleGoogle Scholar
  42. Ma JF, Yamaji N. Silicon uptake and accumulation in higher plants. Trends Plant Sci. 2006;11(8):392–7.PubMedView ArticleGoogle Scholar
  43. Mader JS, Hoskin DW. Cationic antimicrobial peptides as novel cytotoxic agents for cancer treatment. Expert Opin Investig Drugs. 2006;15(8):933–46.PubMedView ArticleGoogle Scholar
  44. Makandar R, Essig JS, Schapaugh MA, Trick HN, Shah J. Genetically engineered resistance to fusarium head blight in wheat by expression of Arabidopsis NPR1. Mol Plant Microbe Interact. 2006;19(2):123–9.PubMedView ArticleGoogle Scholar
  45. Maruthasalam S, Kalpana K, Kumar K, Loganathan M, Poovannan K, Raja J, et al. Pyramiding transgenic resistance in elite indica rice cultivars against the sheath blight and bacterial blight. Plant Cell Rep. 2007;26(6):791–804.PubMedView ArticleGoogle Scholar
  46. Mei CS, Qi M, Sheng GY, Yang YN. Inducible overexpression of a rice allene oxide synthase gene increases the endogenous jasmonic acid level, PR gene expression, and host resistance to fungal infection. Mol Plant Microbe Interact. 2006;19(10):1127–37.PubMedView ArticleGoogle Scholar
  47. Mishra NS, Tuteja R, Tuteja N. Signaling through MAP kinase networks in plants. Arch Biochem Biophys. 2006;452(1):55–68.PubMedView ArticleGoogle Scholar
  48. Mitsuhara I, Iwai T, Seo S, Yanagawa Y, Kawahigasi H, Hirose S, et al. Characteristic expression of twelve rice PR1 family genes in response to pathogen infection, wounding, and defense-related signal compounds (121/180). Mol Gen Genomics. 2008;279(4):415–27.View ArticleGoogle Scholar
  49. Morrissey JP, Osbourn AE. Fungal resistance to plant antibiotics as a mechanism of pathogenesis. Microbiol Mol Biol Rev. 1999;63(3):708–24.PubMedGoogle Scholar
  50. Nakashima K, Tran L-SP, Nguyen DV, Fujita M, Maruyama K, Todaka D, et al. Functional analysis of a NAC-type transcription factor OsNAC6 involved in abiotic and biotic stress-responsive gene expression in rice. Plant J. 2007;51(4):617–30.PubMedView ArticleGoogle Scholar
  51. Nishizawa Y, Saruta M, Nakazono K, Nishio Z, Soma M, Yoshida T, et al. Characterization of transgenic rice plants over-expressing the stress-inducible β-glucanase gene Gns1. Plant Mol Biol. 2003;51(1):143–52.PubMedView ArticleGoogle Scholar
  52. Noutoshi Y, Ito T, Seki M, Nakashita H, Yoshida S, Marco Y, et al. A single amino acid insertion in the WRKY domain of the Arabidopsis TIR-NBS-LRR-WRKY-type disease resistance protein SLH1 (sensitive to low humidity 1) causes activation of defense responses and hypersensitive cell death. Plant J. 2005;43(6):873–88.PubMedView ArticleGoogle Scholar
  53. Ono E, Wong HL, Kawasaki T, Hasegawa M, Kodama O, Shimamoto K. Essential role of the small GTPase Rac in disease resistance of rice. Proc Natl Acad Sci USA. 2001;98(2):759–64.PubMedView ArticleGoogle Scholar
  54. Pandey SP, Somssich IE. The role of WRKY transcription factors in plant immunity. Plant Physiol. 2009;150(4):1648–55.PubMedView ArticleGoogle Scholar
  55. Peng H, Zhang Q, Li Y, Lei C, Zhai Y, Sun X, et al. A putative leucine-rich repeat receptor kinase, OsBRR1, is involved in rice blast resistance. Planta. 2009;230(2):377–85.PubMedView ArticleGoogle Scholar
  56. Peterhänsel C, Lahaye T. Be fruitful and multiply: gene amplification inducing pathogen resistance. Trends Plant Sci. 2005;10(6):257–60.PubMedView ArticleGoogle Scholar
  57. Peters RJ. Uncovering the complex metabolic network underlying diterpenoid phytoalexin biosynthesis in rice and other cereal crop plants. Phytochemistry. 2006;67(21):2307–17.PubMedView ArticleGoogle Scholar
  58. Petersen M, Brodersen P, Naested H, Andreasson E, Lindhart U, Johansen B, et al. Arabidopsis MAP kinase 4 negatively regulates systemic acquired resistance. Cell. 2000;103(7):1111–20.PubMedView ArticleGoogle Scholar
  59. Pinto YM, Kok RA, Baulcombe DC. Resistance to rice yellow mottle virus (RYMV) in cultivated African rice varieties containing RYMV transgenes. Nat Biotechnol. 1999;17(7):702–7.PubMedView ArticleGoogle Scholar
  60. Qiu D, Xiao J, Ding X, Xiong M, Cai M, Cao Y, et al. OsWRKY13 mediates rice disease resistance by regulating defense-related genes in salicylate- and jasmonate-dependent signaling. Mol Plant Microbe Interact. 2007;20(5):492–9.PubMedView ArticleGoogle Scholar
  61. Qiu D, Mao J, Yang X, Zeng H. Expression of an elicitor-encoding gene from Magnaporthe grisea enhances resistance against blast disease in transgenic rice. Plant Cell Rep. 2009a;28(6):925–33.PubMedView ArticleGoogle Scholar
  62. Qiu D, Xiao J, Xie W, Cheng H, Li X, Wang S. Exploring transcriptional signalling mediated by OsWRKY13, a potential regulator of multiple physiological processes in rice. BMC Plant Biol. 2009b;9:74.PubMedView ArticleGoogle Scholar
  63. Qu L-J, Chen J, Liu M, Pan N, Okamoto H, Lin Z, et al. Molecular cloning and functional analysis of a novel type of Bowman-Birk inhibitor gene family in rice. Plant Physiol. 2003;133(2):560–70.PubMedView ArticleGoogle Scholar
  64. Qu SH, Liu GF, Zhou B, Bellizzi M, Zeng LR, Dai LY, et al. The broad-spectrum blast resistance gene Pi9 encodes a nucleotide-binding site-leucine-rich repeat protein and is a member of a multigene family in rice. Genetics. 2006;172(3):1901–14.PubMedView ArticleGoogle Scholar
  65. Quilis J, Penas G, Messeguer J, Brugidou C, Segundo BS. The Arabidopsis AtNPR1 inversely modulates defense responses against fungal, bacterial, or viral pathogens while conferring hypersensitivity to abiotic stresses in transgenic rice. Mol Plant Microbe Interact. 2008;21(9):1215–31.PubMedView ArticleGoogle Scholar
  66. Savary S, Willocquet L, Elazegui FA, Castilla NP, Teng PS. Rice pest constraints in tropical Asia: quantification of yield losses due to rice pests in a range of production situations. Plant Dis. 2000;84(3):357–69.View ArticleGoogle Scholar
  67. Sawada K, Hasegawa M, Tokuda L, Kameyama J, Kodama O, Kohchi T, et al. Enhanced resistance to blast fungus and bacterial blight in transgenic rice constitutively expressing OsSBP, a rice homologue of mammalian selenium-binding proteins. Biosci, Biotechnol, Biochem. 2004;68(4):873–80.View ArticleGoogle Scholar
  68. Schaffrath U, Mauch F, Freydl E, Schweizer P, Dudler R. Constitutive expression of the defense-related Rir1b gene in transgenic rice plants confers enhanced resistance to the rice blast fungus Magnaporthe grisea. Plant Mol Biol. 2000;43(1):59–66.PubMedView ArticleGoogle Scholar
  69. Shah J, Raghupathy V, Veluthambi K. Enhanced sheath blight resistance in transgenic rice expressing an endochitinase gene from Trichoderma virens. Biotechnol Lett. 2009;31(2):239–44.PubMedView ArticleGoogle Scholar
  70. Shao M, Wang JS, Dean RA, Lin YJ, Gao XW, Hu SJ. Expression of a harpin-encoding gene in rice confers durable nonspecific resistance to Magnaporthe grisea. Plant Biotechnol J. 2008;6(1):73–81.PubMedGoogle Scholar
  71. Shimono M, Sugano S, Nakayama A, Jiang CJ, Ono K, Toki S, et al. Rice WRKY45 plays a crucial role in benzothiadiazole-inducible blast resistance. Plant Cell. 2007;19(6):2064–76.PubMedView ArticleGoogle Scholar
  72. Silverstein KAT, Moskal Jr WA, Wu HC, Underwood BA, Graham MA, Town CD, et al. Small cysteine-rich peptides resembling antimicrobial peptides have been under-predicted in plants. Plant J. 2007;51(2):262–80.PubMedView ArticleGoogle Scholar
  73. Skamnioti P, Gurr SJ. Magnaporthe grisea cutinase2 mediates appressorium differentiation and host penetration and is required for full virulence. Plant Cell. 2007;19(8):2674–89.PubMedView ArticleGoogle Scholar
  74. Song FM, Goodman RM. OsBIMK1, a rice MAP kinase gene involved in disease resistance responses. Planta. 2002;215(6):997–1005.PubMedView ArticleGoogle Scholar
  75. Takakura Y, Che FS, Ishida Y, Tsutsumi F, Kurotani K, Usami S, et al. Expression of a bacterial flagellin gene triggers plant immune responses and confers disease resistance in transgenic rice plants. Mol Plant Pathol. 2008;9(4):525–9.PubMedView ArticleGoogle Scholar
  76. Takase K, Hagiwara K, Onodera H, Nishizawa Y, Ugaki M, Omura T, et al. Constitutive expression of human lactoferrin and its N-lobe in rice plants to confer dideade resistance. Biochem Cell Biology. 2005;83(2):239–49.View ArticleGoogle Scholar
  77. Tao Z, Liu H, Qiu D, Zhou Y, Li X, Xu C, et al. A pair of allelic WRKY genes play opposite role in rice–bacteria interactions. Plant Physiol. 2009;151(2):936–48.PubMedView ArticleGoogle Scholar
  78. Thao NP, Chen L, Nakashima A, Hara SI, Umemura K, Takahashi A, et al. RAR1 and HSP90 form a complex with Rac/Rop GTPase and function in innate-immune responses in rice. Plant Cell. 2007;19(12):4035–45.PubMedView ArticleGoogle Scholar
  79. Tian D, Yin Z. Constitutive heterologous expression of avrXa27 in rice containing the R gene Xa27 confers enhanced resistance to compatible Xanthomonas oryzae strains. Mol Plant Pathol. 2009;10(1):29–39.PubMedView ArticleGoogle Scholar
  80. Till B, Cooper J, Tai T, Colowit P, Greene E, Henikoff S, et al. Discovery of chemically induced mutations in rice by TILLING. BMC Plant Biol. 2007;7(1):19.PubMedView ArticleGoogle Scholar
  81. Toki S, Hara N, Ono K, Onodera H, Tagiri A, Oka S, et al. Early infection of scutellum tissue with Agrobacterium allows high-speed transformation of rice. Plant J. 2006;47(6):969–76.PubMedView ArticleGoogle Scholar
  82. Tu J, Datta K, Khush GS, Zhang Q, Datta SK. Field performance of Xa21 transgenic indica rice (Oryza sativa L.): IR72. TAG. Theor Appl Genet. 2000;101(1):15–20.View ArticleGoogle Scholar
  83. van Loon LC, Rep M, Pieterse CMJ. Significance of inducible defense-related proteins in infected plants. Annu Rev Phytopathol. 2006;44(1):135–62.PubMedView ArticleGoogle Scholar
  84. Vergne E, Ballini E, Droc G, Tharreau D, Nottéghem J-L, Morel J-B. ARCHIPELAGO: a dedicated resource for exploiting past, present, and future genomic data on disease resistance regulation in rice. Mol Plant Microbe Interact. 2008;21(7):869–78.PubMedView ArticleGoogle Scholar
  85. Wang GN, Ding XH, Yuan M, Qiu DY, Li XH, Xu CG, et al. Dual function of rice OsDR8 gene in disease resistance and thiamine accumulation. Plant Mol Biol. 2006;60(3):437–49.PubMedView ArticleGoogle Scholar
  86. White FF, Yang B. Host and pathogen factors controlling the rice–Xanthomonas oryzae interaction. Plant Physiol. 2009;150(4):1677–86.PubMedView ArticleGoogle Scholar
  87. Wong HL, Sakamoto T, Kawasaki T, Umemura K, Shimamoto K. Down-regulation of metallothionein, a reactive oxygen scavenger, by the small GTPase OsRac1 in rice. Plant Physiol. 2004;135(3):1447–56.PubMedView ArticleGoogle Scholar
  88. Xiao W, Liu H, Li Y, Li X, Xu C, Long M, et al. A rice gene of de novo origin negatively regulates pathogen-induced defense response. PLoS ONE. 2009;4(2):e4603.PubMedView ArticleGoogle Scholar
  89. Xiong LZ, Yang YN. Disease resistance and abiotic stress tolerance in rice are inversely modulated by an abscisic acid-inducible mitogen-activated protein kinase. Plant Cell. 2003;15(3):745–59.PubMedView ArticleGoogle Scholar
  90. Yamaguchi T, Kuroda M, Yamakawa H, Ashizawa T, Hirayae K, Kurimoto L, et al. Suppression of a phospholipase D gene, OsPLD beta 1, activates defense responses and increases disease resistance in rice. Plant Physiol. 2009;150(1):308–19.PubMedView ArticleGoogle Scholar
  91. Ye R, Huang H, Yang Z, Chen T, Liu L, Li X, et al. Development of insect-resistant transgenic rice with Cry1C*-free endosperm. Pest Manag Sci. 2009;65(9):1015–20.PubMedView ArticleGoogle Scholar
  92. Yin Z, Chen J, Zeng L, Goh M, Leung H, Khush GS, et al. Characterizing rice lesion mimic mutants and identifying a mutant with broad-spectrum resistance to rice blast and bacterial blight. Mol Plant Microbe Interact. 2000;13(8):869–76.PubMedView ArticleGoogle Scholar
  93. Yuan YX, Zhong SH, Li Q, Zhu ZR, Lou YG, Wang LY, et al. Functional analysis of rice NPR1-like genes reveals that OsNPR1/NH1 is the rice orthologue conferring disease resistance with enhanced herbivore susceptibility. Plant Biotechnol J. 2007;5(2):313–24.PubMedView ArticleGoogle Scholar
  94. Zeng LR, Qu SH, Bordeos A, Yang CW, Baraoidan M, Yan HY, et al. Spotted leaf11, a negative regulator of plant cell death and defense, encodes a U-box/armadillo repeat protein endowed with E3 ubiquitin ligase activity. Plant Cell. 2004;16(10):2795–808.PubMedView ArticleGoogle Scholar
  95. Zhang J, Peng YL, Guo ZJ. Constitutive expression of pathogen-inducible OsWRKY31 enhances disease resistance and affects root growth and auxin response in transgenic rice plants. Cell Research. 2008;18(4):508–21.PubMedView ArticleGoogle Scholar
  96. Zhao B, Lin X, Poland J, Trick H, Leach J, Hulbert S. A maize resistance gene functions against bacterial streak disease in rice. Proc Natl Acad Sci USA. 2005;102(43):15383–8.PubMedView ArticleGoogle Scholar
  97. Zhu Y, Chen H, Fan J, Wang Y, Li Y, Chen J, et al. Genetic diversity and disease control in rice. Nature. 2000;406(6797):718–22.PubMedView ArticleGoogle Scholar
  98. Zhu H, Xu X, Xiao G, Yuan L, Li B. Enhancing disease resistances of super hybrid rice with four antifungal genes. Sci China Ser C: Life Sci. 2007;50(1):31–9.View ArticleGoogle Scholar

Copyright

© The Author(s) 2010