Abstract
BackgroundUncontrolled expression of a certain mitochondrial gene often causes cytoplasmic male sterility (CMS) in plants. This phenotype is prevented by the presence of a fertility restorer (Rf) gene in the nuclear genome. Such CMS/Rf systems have been successfully used for breedings of F1 hybrid cultivars. In rice, approximately 99% of F1 hybrid cultivars have been developed using a wild abortive type of CMS (WA-CMS) and its Rf genes. Recently, a newly identified mitochondrial gene, orf352, was reported as a WA-CMS-causing gene.FindingsWe cloned and functionally characterized Rf4, a major Rf gene for WA-CMS. We revealed that Rf4 encoded a pentatricopeptide repeat-containing protein and reduced the orf352-containing transcripts, thereby restoring pollen fertility.ConclusionsThrough a map-based cloning, we have independently identified an allele of a recently reported Rf4 gene and demonstrated that the fertility restoration is controlled sporophytically.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-014-0028-z) contains supplementary material, which is available to authorized users.
Highlights
Uncontrolled expression of a certain mitochondrial gene often causes cytoplasmic male sterility (CMS) in plants
A wild abortive (WA)-type CMS has been almost exclusively used for breeding three-line hybrid rice and contributes to 10% of the total rice cultivated area worldwide (Li et al 2007; Barclay 2010)
We found a sequence variant of orf352 in an RT102 CMS line derived from O. rufipogon (Okazaki et al 2013)
Summary
Through a map-based cloning, we have independently identified an allele of a recently reported Rf4 gene and demonstrated that the fertility restoration is controlled sporophytically. To identify the Rf4 gene for WA-CMS, we performed map-based cloning of Rf4 using a cultivar IR24 (Additional file 1: “Methods”), because this cultivar is known to be a strong restorer line for WA-CMS (Jing et al 2001). Because the presence of Rf4 reduced the orf352-containing transcripts in the mitochondria, we identified the candidate gene according to the following two criteria, (i) it would encode a protein whose function is related to RNA metabolism, PPR454 PPR782a PPR782b PPR458. In four of the thirteen transgenic plants with PPR782a, restorations of anther and pollen development and starch accumulation in pollen grains were observed (Figure 2a; Additional file 4: Figure S2). Introduction of three other genomic fragments, which contained PPR782b, PPR454, or PPR458, did not recover the anther and pollen morphology (Additional file 4: Figure S2), and resulted in 0% of a WAA
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