What Does the Molecular Genetics of Different Types of <i>Restorer-of-Fertility</i> Genes Imply?

• Main Authors: Tomohiko Kubo, Takumi Arakawa, Yujiro Honma, Kazuyoshi Kitazaki
• Format: Article
• Language: English
• Published: MDPI AG 2020-03-01
• Series: Plants
• Subjects: cytoplasmic male sterility; hybrid breeding; nuclear-mitochondrial interaction; <i>restorer-of-fertility</i>
• Online Access: https://www.mdpi.com/2223-7747/9/3/361

Cytoplasmic male sterility (CMS) is a widely used trait for hybrid seed production. Although male sterility is caused by S cytoplasm (male-sterility inducing mitochondria), the action of S cytoplasm is suppressed by <i>restorer-of-fertility</i> (<i>Rf</i>), a nuclear gene. Hence, the genetics of <i>Rf</i> has attained particular interest among plant breeders. The genetic model posits <i>Rf</i> diversity in which an <i>Rf</i> specifically suppresses the cognate S cytoplasm. Molecular analysis of <i>Rf</i> loci in plants has identified various genes; however, pentatricopeptide repeat (PPR) protein (a specific type of RNA-binding protein) is so prominent as the <i>Rf</i>-gene product that <i>Rf</i>s have been categorized into two classes, PPR and non-PPR. In contrast, several shared features between PPR- and some non-PPR <i>Rf</i>s are apparent, suggesting the possibility of another grouping. Our present focus is to group <i>Rf</i>s by molecular genetic classes other than the presence of PPRs. We propose three categories that define partially overlapping groups of <i>Rf</i>s: association with post-transcriptional regulation of mitochondrial gene expression, resistance gene-like copy number variation at the locus, and lack of a direct link to <i>S-orf</i> (a mitochondrial ORF associated with CMS). These groups appear to reflect their own evolutionary background and their mechanism of conferring S cytoplasm specificity.