The Wild-Abortive cytoplasmic male sterility (CMS-WA) system is widely used for hybrid rice breeding. Recently, we reported that a novel, chimeric mitochondrial gene, WA352, causes CMS-WA by inducing premature tapetalprogrammed cell death. Two major restorer genes, Rf3 and Rf4, control fertility restoration of CMS-WA. Here we report the cloning and functional examination of Rf4. We mapped Rf4 to a chromosomal region within a cluster of genes encoding pentatricopeptide repeat (PPR) proteins. We then used functional complementation to identify Rf4 as PPR9-782-M, a gene in a restorer line; a transgene of PPR9-782-M restores fertility in WA-cytoplasm plants. Rf4 encodes a mitochondrion-targeted PPR protein of 782 amino acids. Rf4 and its closely-linked homologs show highly-diverged sequences in different rice cultivars. The PPR9-782-M transgenic plants showed decreased levels of WA352 mRNA, suggesting that RF4 (PPR9-782-M) may function in post-transcriptional degradation of WA352 transcripts. Our study provides crucial basis for finding nuclear-encoded interactor(s) of RF4 and elucidating the corresponding molecular mechanism of CMS restoration. In addition, our results have practical implications for hybrid rice breeding.
Tang H, Luo D, Zhou D, Zhang Q, Tian D, Zheng X, Chen L*, Liu YG* (2014) The Rice Restorer Rf4 for Wild-Abortive Cytoplasmic Male Sterility Encodes a Mitochondrial-Localized PPR Protein that Functions in Reduction of WA352 Transcripts. Molecular Plant. 1497-500 [full text]