Sequence Diversity of SLG and SRK in Brassica oleracea L.

DNA sequences of SLG and SRK, believed to function in self-pollen recognition of self-incompatibility, were analysed and compared between many S haplotypes of Brassica oleracea. Some different S haplotypes have highly similar SLGs (more than 97·5% amino acid sequence identity), while their SRKs are less similar (less than 88% identity). Different lines having the same recognition specificity often show a high degree of sequence variation in SLG (88·5% identity in the S2 haplotype), but their SRKs are very similar to each other (97·3% identity). S haplotypes, in which SLG protein is undetectable by Western blot analysis, have stop codons in the middle of the coding region of SLG, or lack an SLG gene in the genome, suggesting that these haplotypes do not synthesize the functional SLG protein. The SRK alleles in these haplotypes are normal. The function of SLG and SRK in self-incompatibility and the evolution of these alleles are discussed.