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Cytoplasmic male sterility (CMS) determined by mitochondrial genes and restorer of fertility (

Cytoplasmic male sterility (CMS) determined by mitochondrial genes and restorer of fertility ( Rf ) controlled by nuclear-encoded genes provide the breeding systems of many hybrid crops for the utilization of heterosis. Although several CMS/ Rf systems have been widely exploited in rice, hybrid breeding using these systems has encountered difficulties due to either fertility instability or complications of two-locus inheritance or both. In this work, we characterized a type of CMS, Fujian Abortive cytoplasmic male sterility (CMS-FA), with stable sporophytic male sterility and a nuclear restorer gene that completely restores hybrid fertility. CMS is caused by the chimeric open reading frame FA182 that specifically occurs in the mitochondrial genome of CMS-FA rice. The restorer gene OsRf19 encodes a pentatricopeptide repeat (PPR) protein targeted to mitochondria, where it mediates the cleavage of FA182 transcripts, thus restoring male fertility. Comparative sequence analysis revealed that OsRf19 originated through a recent duplication in wild rice relatives, sharing a common ancestor with OsRf1a / OsRf5 , a fertility restorer gene for Boro II and Hong-Lian CMS. We developed six restorer lines by introgressing OsRf19 into parental lines of elite CMS-WA hybrids; hybrids produced from these lines showed equivalent or better agronomic performance relative to their counterparts based on the CMS-WA system. These results demonstrate that CMS-FA/ OsRf19 provides a highly promising system for future hybrid rice breeding.

The Fujian Abortion cytoplasmic male sterility (CMS-FA) system, a new type of sporophytic CMS system in indica rice (Oryza sativa L.), was developed using the cytoplasm and the corresponding fertility-restoring gene from a wild rice (O. rufipogon L.), which originated from Fujian Province, China. Previous studies in combination with several years of production practice demonstrated that CMS-FA hybrid rice was superior to CMS-WA hybrid rice, a prevailing hybrid rice worldwide, and that the male fertility restoration was controlled by a pair of dominant alleles. We tentatively designated the fertility restoration gene as Rf(fa). The analysis of the polymorphism between the fertile and sterile pool DNAs from a mapping segregation population (BC1F1) indicated that Rf(fa) was located on rice chromosome 10. We further delimited the Rf(fa) locus to a 121.1-kb region flanked by RM6100 and MM2023, which were approximately 0.26 cM and 0.18 cM away from Rf(fa), respectively, by simple sequence repeat molecular marker linkage genetic analysis. These results would facilitate the map-based cloning of Rf(fa), the elucidation of a novel molecular mechanism underlying cytoplasm–nucleus interaction in the CMS-FA system, and the production application of this hybrid rice.