What Does the Molecular Genetics of Different Types of Restorer-of-Fertility Genes Imply?

Abstract

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 restorer-of-fertility (Rf), a nuclear gene. Hence, the genetics of Rf has attained particular interest among plant breeders. The genetic model posits Rf diversity in which an Rf specifically suppresses the cognate S cytoplasm. Molecular analysis of Rf loci in plants has identified various genes; however, pentatricopeptide repeat (PPR) protein (a specific type of RNA-binding protein) is so prominent as the Rf-gene product that Rfs have been categorized into two classes, PPR and non-PPR. In contrast, several shared features between PPR- and some non-PPR Rfs are apparent, suggesting the possibility of another grouping. Our present focus is to group Rfs by molecular genetic classes other than the presence of PPRs. We propose three categories that define partially overlapping groups of Rfs: 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 S-orf (a mitochondrial ORF associated with CMS). These groups appear to reflect their own evolutionary background and their mechanism of conferring S cytoplasm specificity.

A Lineage-Specific Paralog of Oma1 Evolved into a Gene Family from Which a Suppressor of Male Sterility-Inducing Mitochondria Emerged in Plants

“…Therefore, it is valuable to compare the evolutionary patterns of the RFL and RF-Oma1 families. Although their gene products and functions are completely different, they share the features of gene clustering and copy number variation ( Kubo et al. 2020 ).…”

“…Rf genes have been identified and analyzed in many plant species, and they encode several different types of proteins ( Kubo et al. 2020 ).…”

Genetic architecture of male fertility restoration in a hybrid breeding system of rye (Secale cereale L.)

“…On basis of male fertility restoration requirements and genetic similarity of sterilizing cytoplasms G, C, and R-type CMS systems have been proposed to belong to the larger Vavilovii (V) type 6,93,94 . In a comprehensive study by Lapinski and Stojalowski 6 on rye populations from 23 countries, the vast majority of male sterility sources were found to belong to the V-type.…”

Identification of microRNAs and their targets in inflorescences of an Ogura-type cytoplasmic male-sterile line and its maintainer fertile line of turnip (Brassica rapa ssp. rapifera) via high-throughput sequencing and degradome analysis

“…The effects of mitochondrial genes governing CMS can be suppressed by nuclear restorer-of-fertility ( Rf ) genes, which mostly encode pentatricopeptide repeat (PPR) proteins [ 12 ]. To date, numerous and variable Rf s or Rf candidates have been identified [ 17 ]. It is well established that the CMS phenotype is due to incompatibility resulting from the combination of mitochondrial dysfunction and a lack of Rf genes [ 1 , 2 ].…”

“…It is well established that the CMS phenotype is due to incompatibility resulting from the combination of mitochondrial dysfunction and a lack of Rf genes [ 1 , 2 ]. However, one fact that cannot be ignored is that nuclear genes affect the expression and function of cytoplasmic genes, as evidenced by the presence of nuclear fertility restorers, and mutant mitochondrial gene expression also contributes to retrograde regulation that fine-tunes nuclear gene expression, thus affecting pollen development [ 2 , 17 – 20 ]. Mitochondrial retrograde regulation especially manifests with variation in the stages at which pollen/anther abortion occur and the inconsistency in microsporogenesis and tapetum development processes with specific mitochondrial genes in different nuclear backgrounds [ 21 – 24 ].…”