Abstract
Restorer-of-fertility (Rf) is a suppressor of cytoplasmic male sterility (CMS), a mitochondrion-encoded trait that has been reported in many plant species. The occurrence of CMS is considered to be independent in each lineage; hence, the question of how Rf evolved was raised. Sugar beet Rf resembles Oma1, a gene for quality control of the mitochondrial inner membrane. Oma1 homologues comprise a small gene family in the sugar beet genome, unlike Arabidopsis and other eukaryotes. The sugar beet sequence that best matched Arabidopsis atOma1 was named bvOma1; sugar beet Rf (RF1-Oma1) was another member. During anther development, atOma1 mRNA was detected from the tetrad to the microspore stages, whereas bvOma1 mRNA was detected at the microspore stage and RF1-Oma1 mRNA was detected during the meiosis and tetrad stages. A transgenic study revealed that, whereas RF1-Oma1 can bind to a CMS-specific protein and alter the higher-order structure of the CMS-specific protein complex, neither bvOma1 nor atOma1 show such activity. We favour the hypothesis that an ancestral Oma1 gene duplicated to form a small gene family, and that one of the copies evolved and acquired a novel expression pattern and protein function as an Rf, i.e. RF1-Oma1 evolved via neofunctionalization.
Highlights
In plants, hermaphrodites are converted into females by male sterility encoded by mitochondria, a phenomenon known as cytoplasmic male sterility (CMS) [1,2]
We hypothesized that there might be another Oma1 homologue that functions as the authentic Oma1 in sugar beet. If so, identifying this sequence will facilitate determining how Oma1-like genes at the Rf1 locus evolved from Oma1. We found that another Oma1-like gene, with the consensus HExxH motif, is preserved in the sugar beet genome; its translation product is incapable of binding preSATP6 protein or generating the 200 kDa protein complex
We propose that in sugar beet, Rf1 evolved via neofunctionalization
Summary
Hermaphrodites are converted into females by male sterility encoded by mitochondria, a phenomenon known as cytoplasmic male sterility (CMS) [1,2]. Translation products from preSatp were detected in all examined organs to form a 250 kDa protein complex in the mitochondrial membrane of CMS plants [16], this complex’s function is unknown. We hypothesized that there might be another Oma homologue that functions as the authentic Oma in sugar beet If so, identifying this sequence will facilitate determining how Oma1-like genes at the Rf1 locus (hereafter RF1-Oma1) evolved from Oma. If so, identifying this sequence will facilitate determining how Oma1-like genes at the Rf1 locus (hereafter RF1-Oma1) evolved from Oma1 We found that another Oma1-like gene, with the consensus HExxH motif, is preserved in the sugar beet genome; its translation product is incapable of binding preSATP6 protein or generating the 200 kDa protein complex. We propose that in sugar beet, Rf1 evolved via neofunctionalization
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