Fujian cytoplasmic male sterility and the fertility restorer gene <i>OsRf19</i> provide a promising breeding system for hybrid rice.

Abstract

Cytoplasmic male sterility (CMS) determined by mitochondrial genes and restorer of fertility (<i>Rf</i>) controlled by nuclear-encoded genes provide the breeding systems of many hybrid crops for the utilization of heterosis. Although several CMS/<i>Rf</i> 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 <i>FA182</i> that specifically occurs in the mitochondrial genome of CMS-FA rice. The restorer gene <i>OsRf19</i> encodes a pentatricopeptide repeat (PPR) protein targeted to mitochondria, where it mediates the cleavage of <i>FA182</i> transcripts, thus restoring male fertility. Comparative sequence analysis revealed that <i>OsRf19</i> originated through a recent duplication in wild rice relatives, sharing a common ancestor with <i>OsRf1a</i>/<i>OsRf5</i>, a fertility restorer gene for Boro II and Hong-Lian CMS. We developed six restorer lines by introgressing <i>OsRf19</i> 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/<i>OsRf19</i> provides a highly promising system for future hybrid rice breeding.