Unravelling Self-Incompatibility in the Asteraceae: Cloning of the S Locus in Chicory (Cichorium intybus L).

In angiosperms, approximately 90 % of species are hermaphrodite. Though this sexual strategy heightens the chance of producing offspring, it is frequently associated with mating systems that promote outcrossing and prevent inbreeding depression. Selfincompatibility (SI) is the widespread mating system promoting outcrossing and is present in over 50 % of species. In most cases, SI is controlled by a single multi-allelic locus, the S-locus, which contains closely linked genes encoding the male and female determinants of pollen–pistil recognition. Two major genetic forms of SI are recognized: in gametophytic SI the incompatibility phenotype of the pollen is determined by its own haploid genotype, whereas in sporophytic SI (SSI) it is determined by the diploid genotype of the parent plant.

In Asteraceae, over 60 % of species are estimated to be self-incompatible with sporophytic genetic determination. To date, male and female determinants underlying SSI in this family are unknown, but are different of those identified in Brassicaceae. Chicory possesses a SSI system, and genetic and physical mapping of the S-locus were undertaken to identify the genes encoding pollen and stigma determinants by positional cloning. In parallel, transcriptomic analyses of stigma-style tissue by RNAseq were performed to identify S-locus candidate genes for the female determinant. The progress of this work is presented, as well as strategies to validate the candidate genes. Perspectives of the molecular characterization of the S-locus in an Asteraceae species for studies on the occurrence, evolution, and origin of SSI, and its role in domestication and invasiveness are addressed.