Identification of the fertility restoration locus, Rfo, in radish, as a member of the pentatricopeptide‐repeat protein family

Abstract

Ogura cytoplasmic male sterility (CMS) in radish (Raphanus sativus) is caused by an aberrant mitochondrial gene, Orf138, that prevents the production of functional pollen without affecting female fertility. Rfo, a nuclear gene that restores male fertility, alters the expression of Orf138 at the post-transcriptional level. The Ogura CMS/Rfo two-component system is a useful model for investigating nuclear-cytoplasmic interactions, as well as the physiological basis of fertility restoration. Using a combination of positional cloning and microsynteny analysis of Arabidopsis thaliana and radish, we genetically and physically delimited the Rfo locus to a 15-kb DNA segment. Analysis of this segment shows that Rfo is a member of the pentatricopeptide repeat (PPR) family. In Arabidopsis, this family contains more than 450 members of unknown function, although most of them are predicted to be targeted to mitochondria and chloroplasts and are thought to have roles in organellar gene expression.

QTL involved in the partial restoration of male fertility of C-type cytoplasmic male sterility in maize

“…The clustering of restorer genes in maize corresponds to the complex genomic structure of restorer loci in other plants such as petunia, radish and rice, where restorer genes are found near highly homologous genes of the pentatricopeptide-repeat (PPR) family (Bentolila et al 2002;Desloire et al 2003;Wang et al 2008). Furthermore, clusters of uncharacterized restorer genes were found in cotton (Zhang and Stewart 2001) and rapeseed (Li et al 1998).…”

The Rf and Rf-like PPR in higher plants, a fast-evolving subclass of PPR genes

“…[13][14][15] These sister CMS are caused by the orf138 (Ogura) or the orf125 (Kosena) mitochondrial genes, which encode almost identical sterilityinducing proteins showing no homology with any other known proteins. [30][31][32] Both CMS originates from radish and were successfully transferred to rapeseed (Brassica napus) by protoplast fusion.…”

“…In the last years, several Rf genes were cloned from various crop species and the majority of them encode proteins belonging to the pentatricopeptide repeat family (PPR) (summarized in Table 1). 6,[12][13][14][15][16][17] All these restoring PPR proteins (hereafter called Rf-PPR) were shown to target the mitochondrion and act by specifically reducing the accumulation of their cognate CMS-associated mitochondrial RNAs and/or proteins. The prevalence of PPR proteins in plastid and mitochondrial RNA processing is now largely documented 18 and the fact that many Rf genes were found to encode PPR proteins is coherent CMS/Rf systems to serve as precious models to study nucleomitochondrial genetic interactions in plants.…”

“…Sequence alignments have also revealed that most identified Rf-PPRs show strong sequence similarity with a group of 10-30 PPR proteins encoded in the species in which they were found or in closely related species. 13,23 These proteins constitute the subgroup of Rf-like (RFL) PPR proteins. Recent large-scale phylogenetic analyses have further shown that RFL and Rf-PPR proteins constitute an evolutionary distinct subgroup of proteins within the PPR family in angiosperms and that all identified Rf-PPR genes have evolved from this unique group of PPR genes.…”

“…Cloning of the associated restorer genes showed that Ogura and Kosena CMS Rf loci are identical and encode three highly similar PPR proteins out of which only one, PPR-B, carries the restoration activity. [13][14][15] PPR-B encodes a protein composed of 687 amino acid and 17 PPR repeats that is partly associated with mitochondrial membranes. 33 Expression analysis in rapeseed transgenic plants showed that PPR-B protein accumulates preferentially in anthers of restored plants.…”