The S15 self-incompatibility haplotype in Brassica oleracea includes three S gene family members expressed in stigmas

Self-incompatibility in Brassica is controlled by a single, highly polymorphic locus that extends over several hundred kilobases and includes several expressed genes. Two stigma proteins, the S locus receptor kinase (SRK) and the S locus glycoprotein (SLG), are encoded by genes located at the S locus and are thought to be involved in the recognition of seif-pollen by the stigma. We report here that two different SLG genes, SLGA and SLOB, are located at the S locus in the class II, pollen-recessive S-15 haplotype, Both genes are interrupted by a single intron; however, SLGA encodes both soluble and membrane-anchored forms of SLG, whereas SLOB encodes only soluble SLG proteins. Thus, including SRK, the S locus in the S-15 haplotype contains at least three members of the S gene family. The protein products of these three genes have been characterized, and each SLG glycoform was assigned to an SLG gene. Evidence is presented that the S-2 and S-5 haplotypes carry only one or the other of the SLG genes, indicating either that they are redundant or that they are not required for the self-incompatibility response.