Fig. 7

Model of a nuclear female sterility system for mechanization of hybrid seed production in rice. The restorer line was created by transformation of wild-type commercial line MH86 with a vector construct containing three transgene expression cassettes: (i) the WT fertility gene (FS) to restore the female fertility, (ii) the α-amylase gene (AAM) to devitalize transgenic pollens, and (iii) the red fluorescence protein (RFP) gene to distinguish the transgenic seeds from the non-transgenic seeds. A hemizygous transgene in the female sterile mutant plant can fully restore the female fertility since the female fertility gene is a recessive sporophytic gene. The α-amylase gene, driven by a pollen-specific promoter, disrupts starch accumulation only in the transgenic pollen so only the transgenic pollen grains produced by the hemizygous transgenic plant are defective, while the non-transgenic pollen grains are viable for pollination. The resulting transgenic maintainer plant (FS, FS-AAM-RFP//fs) produces male gametes (MG) of one genotype (fs) and female gametes (FG) of two genotypes (fs and FS, FS-AAM-RFP). Self-pollination of the transgenic maintainer line generates the transgenic seed (FS, FS-AA-RFP//fs) and female sterile seed (fs//fs) in a 1:1 ratio, and the seeds can be sorted based on red fluorescence. The female sterile seeds can be propagated via self-pollination. The female sterile plants (paternal line) can be pollinated with male sterile plants (maternal line) for mechanized production of hybrid seeds. The restorer was transformed with vector pFS4