Hybrid production in cereals requires a way to control self-pollination of plants. A system that has been successfully used for breeding hybrids in some plant species is based on cytoplasmic male sterility (CMS). CMS is induced by mitochondriallyencoded genes whose expression results in plant sterility. Nuclear-encoded Restorer of Fertility (RF) genes restore plant fertility by blocking expression of CMS-transcripts. The majority of to date identified RF genes form a distinct clade in the family of the pentatricopeptide repeat proteins, sequence-specific RNA-binding factors located to organelles and involved in intron splicing, RNA editing and cleavage of transcripts. The PPR family is one of the largest gene families in flowering plants and counts typically 550-700 PPR genes.

Interestingly in the wheat IWGSC RefSeq v1.0 genome we found 1686 PPRs, of which 207 were identified as restorer of fertility-like (RFL), far more than in any other plant genome analysed to date. The large number of PPR and RFL genes is primarily due to polyploidy and it’s actually lower than expected from simply adding genes present in the progenitor diploid genomes. This implies PPR gene inactivation and loss during polyploidization, for which we found evidence in the form of truncated or frame-shifted gene fragments.

In addition, we show that locations of some of the previously mapped restorer genes overlap with the genomic locations of RFL clusters identified in our study. This is the first comprehensive analysis of the PPR and RFL family in wheat. The sequence knowledge gained from this project has the potential to accelerate the hybrid wheat breeding programs by facilitating the identification of active restorer genes in potential restorer lines. Hybrid wheat varieties are expected to have higher and more consistent yields by better adaptation to increasingly unpredictable weather conditions in the era of global climate change.

THEME 5