Identification of candidate genes for self-compatibility in perennial ryegrass (Lolium perenneL.)

Abstract

Self-incompatibility (SI) is a genetic mechanism preventing self-pollination in approximately 40% of plant species. Two multiallelic loci, called S and Z, control the gametophytic SI system of the grass family (Poaceae), which contains all major forage grasses. Loci independent from S and Z have been reported to disrupt SI and lead to self-compatibility (SC). A locus causing SC in perennial ryegrass (Lolium perenne L.) was previously mapped on linkage group (LG) 5 in a F2 population segregating for SC. Using a subset of the same population (n=73), we first performed low-resolution quantitative trait locus (QTL) mapping to exclude the presence of additional, previously undetected contributors to SC. The previously reported QTL on LG 5 explained 38.4% of the phenotypic variation, and no significant contribution from other genomic regions was found. This was verified by the presence of significantly distorted markers in the region overlapping with the QTL. Second, we fine mapped the QTL to 0.26 cM using additional 2,056 plants and 23 novel sequence-based markers. Using an Italian ryegrass (Lolium multiflorum Lam.) genome assembly as reference, the markers flanking SC were estimated to span a ~3 Mb region encoding for 57 predicted genes. Among these, seven genes were proposed as relevant candidate genes based on their annotation and function described in previous studies. Our work is a step forward to identify SC genes in forage grasses and provides diagnostic markers for marker-assisted introgression of SC into elite germplasm.

Characterization and practical use of self-compatibility in outcrossing grass species

“…Genes underlying these loci likely have a function in the downstream cascade following the initial pollen–stigma recognition mediated by S and Z ( Do Canto et al , 2016 ). The most recent studies on non- S or non- Z sources of SC identified two genetically independent loci on LG 5 ( Arias-Aguirre et al , 2013 ; Do Canto et al , 2018 ; Cropano et al , 2021 ) and LG 6 ( Slatter et al , 2020 ) in two unrelated perennial ryegrass F 2 populations segregating for SC. In both populations, using in vitro self-pollinations ( Fig.…”

“…In both cases, it was concluded that SC was under the control of a single gametophytically acting pollen gene. Furthermore, Cropano et al (2021) narrowed down the region to a 0.26-cM locus, allowing the identification of candidate genes that could be the target of functional characterization studies.…”

Genetic control of compatibility in crosses between wheat and its wild or cultivated relatives

“…The fact that both the S and Z candidates contain the same protein domain (DUF247) of unknown function warrants further investigation into the molecular role and evolutionary origin of this domain. Recently, this same team fine mapped a QTL for self‐compatibility (SC) on chromosome 5 of L. perenne (Cropano et al ., 2021). They reduced the region to a 3‐Mb segment containing 57 genes among which, seven were relevant candidates.…”