The knockdown of OsVIT2 and MIT affects iron localization in rice seed
© Bashir et al.; licensee Springer. 2013
Received: 14 May 2013
Accepted: 12 September 2013
Published: 20 November 2013
The mechanism of iron (Fe) uptake in plants has been extensively characterized, but little is known about how Fe transport to different subcellular compartments affects Fe localization in rice seed. Here, we discuss the characterization of a rice vacuolar Fe transporter 2 (OsVIT2) T-DNA insertion line (osvit2) and report that the knockdown of OsVIT2 and mitochondrial Fe transporter (MIT) expression affects seed Fe localization.
osvit2 plants accumulated less Fe in their shoots when grown under normal or excess Fe conditions, while the accumulation of Fe was comparable to that in wild-type (WT) plants under Fe-deficient conditions. The accumulation of zinc, copper, and manganese also changed significantly in the shoots of osvit2 plants. The growth of osvit2 plants was also slow compared to that of WT plants. The concentration of Fe increased in osvit2 polished seeds. Previously, we reported that the expression of OsVIT2 was higher in MIT knockdown (mit-2) plants, and in this study, the accumulation of Fe in mit-2 seeds decreased significantly.
These results suggest that vacuolar Fe trafficking is important for plant Fe homeostasis and distribution, especially in plants grown in the presence of excess Fe. Moreover, changes in the expression of OsVIT2 and MIT affect the concentration and localization of metals in brown rice as well as in polished rice seeds.
Iron (Fe) is an essential micronutrient for all higher organisms. Plants require Fe for several cellular processes, including respiration, chlorophyll biosynthesis, and photosynthetic electron transport (Marschner 1995). The molecular mechanism of Fe transport in rice has been well documented (Bashir et al. 2006; Bashir and Nishizawa 2006; Bashir et al. 2010; Bashir et al. 2011b; Bashir et al. 2013a; Ishimaru et al. 2012; Kobayashi and Nishizawa 2012). Once inside a plant, Fe enters root cells and is transported to the shoot and seeds. Fe performs vital roles in subcellular organelles such as chloroplasts and mitochondria, and defects in mitochondrial Fe homeostasis significantly affect plant growth (Bashir et al. 2011a; Bashir et al. 2011c; Ishimaru et al. 2009). As excess Fe in the cytoplasm may be toxic, it is either stored as ferritin in chloroplasts or is diverted to the vacuole. Knockout mutants for the rice vacuolar metal transporters OsVIT1 and OsVIT2 were recently reported to accumulate increased amounts of Fe in their seeds (Zhang et al. 2012). This accumulation was mainly observed in the embryo (Zhang et al. 2012), which is removed during milling. In this short report, we describe the characterization of a mutant in which the expression of OsVIT2 was knocked down and we show that changes in the expression of OsVIT2 and mitochondrial iron transporter (MIT) affect seed Fe localization in brown rice as well as in polished rice seeds.
This study was supported by a grant from the Ministry of Agriculture, Forestry and Fisheries of Japan (Green Technology Project IP-5003).
In our previous report (Bashir et al. 2011c), OsVIT2 was referred to as OsVIT1, while Zhang et al. (2012) used the name OsVIT2 for the same gene. To avoid confusion, in this study we changed the name of OsVIT1 to OsVIT2.
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