Genomic Organization of the SLG/SRK Region of the S Locus in Brassica Species

Self-incompatibility in Brassica species is controlled by a single S locus with multiple alleles. Recent experimental data suggest that SLG (S locus glycoprotein) and/or SRK (S receptor kinase) are the stigmatic S determinants of self-incompatibility in Brassica. A 76-kb genomic fragment containing both SLG and SRK was isolated and characterized in the S9 haplotype of B. campestris. This fragment contains at least 14 expressed genes and three putative open reading frames (ORFs), suggesting that the S locus is embedded in a gene-rich region. Within this fragment, both anther and/or stigma-specific genes are clustered around the SLG and SRK genes. Some members of the S multigene family are also closely linked to the S locus. In this review we discuss the complex genomic structure of the S locus in Brassica species.