Self-incompatibility in ryegrass: Homing in on the genes of the S-locus complex

Self-incompatibility (SI) is a genetic mechanism that prevents self-pollination by using a system of recognition between the pollen and the stigma. The genetic control of this mechanism in grasses is hardly understood. In perennial ryegrass(Lolium perenne L.), SI is controlled by at least two loci, S and Z (Lundqvist, 1954; Hayman, 1956) which have not been characterized in any grass species yet. The S-locus in perennial ryegrass has been mapped on linkage group 1(Thorogood et al., 2002) but, to date, mapping approaches for gene isolation and cloning have been inconclusive. Using mapping populations especially designed to map the S-locus, fine-mapping has been conducted by genotypingover 10,000 plants using high resolution melting curve analysis (HRM). So far, the two closest recombinant flanking markers of the S-locus have been mapped at 0.06cM and 0.01cM either side of the S-locus region that contains 6 genes in the rice and 9 genes in the Brachypodium homologous regions. Using these markers as well as several non-recombinant markers, contiguous Lolium BAC clones covering this region have been isolated, sequenced and assembled in order to build up the physical region of the S-locus. Moreover, RNA-seq from stigma and pollen tissue, as well as stigmas pollinated with incompatible and -compatible pollen, has been conducted to corroborate expressed candidate genes and to identify the causative polymorphism that is the basis of S locus specificity