Identification of genomic regions and genes encoding for Diallelic Self-incompatibility (DSI) and sex in Oleaceae

The diversity of mating and sexual systems in Angiosperms is spectacular, but the factors driving their evolution remain poorly understood. In plants of the Oleaceae family, an unusual self-incompatibility (SI) system has been discovered recently, whereby only two distinct homomorphic SI specificities segregate stably. To understand the role of this peculiar SI system in preventing or promoting the diversity of sexual phenotypes observed across the family, an essential first step is to characterize the genetic architecture of these two traits.In the present project, we developed a high-density genetic map of the androdioecious shrub P. angustifolia based on a F1 cross between a hermaphrodite and a male parent with distinct SI genotypes. Using a double restriction-site associated digestion (ddRAD) sequencing approach, we obtained reliable genotypes for 196 offspring and their two parents, constructed a genetic map and found strong signals of association for the sex and SI phenotypes demonstrating inheritance of these traits as single, independent, mendelian factors. The P. angustifolia linkage map shows robust synteny to the olive tree genome overall. Two of the six markers strictly associated with SI in P. angustifolia have strong similarity with a recently identified 741kb chromosomal region fully linked to the SI phenotype on chromosome 18 of the olive tree genome, providing strong cross-validation support. This P. angustifolia linkage map will be a useful resource to investigate the various ways by which the sex and SI determination systems have co-evolved in the broader phylogenetic context of the Oleaceae family.