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

Abstract The ‘Gülzow’ (G) type cytoplasmic male sterility (CMS) system in hybrid rye (Secale cereale L.) breeding exhibits a strong and environmentally stable restoration of male fertility (Rf). While having received little scientific attention, three G-type Rf genes had been identified on 4RL (Rfg1) and two minor genes on 3R (Rfg2) and 6R (Rfg3) chromosome. Here, we report a comprehensive investigation of the genetics underlying restoration of male fertility in a large G-type CMS breeding system using a palette of complementing forward and reverse genetic analysis. This includes (i) genome wide association studies (GWAS) on a G-type germplasm, (ii) GWAS on a biparental mapping population, (iii) in silico identification of Rf-like pentatricopeptide repeat (RFL-PPR) genes and their expressed in G-type rye hybrids, and (iv) mining patterns in linkage disequilibrium. Our findings provide compelling evidence of a novel major G-type non-PPR Rf gene on the 3RL chromosome. In the in silico analysis, we identified 22 RFL-PPR of which 15 were expressed in the transcriptome of G-type hybrids. Our findings provides a novel insight into the underlying genetics of male fertility restoration in a G-type CMS system in rye. The discovery made in this study is distinct to known P- and C-type systems in rye in addition to known CMS systems in barley and wheat. This study constitutes a steppingstone towards understanding the restoration of male fertility in G-type CMS system and a potential resources for addressing the inherent issues of the P-type system.