Physical distances between S-locus genes in various S haplotypes of Brassica rapa and B-oleracea

In Brassica, self-incompatibility genes SLG (for S-locus glycoprotein) and SRK (for S-receptor kinase) are located in the S-locus complex region with several other S-linked genes. The S locus is a highly polymorphic region: p olymorphism has been observed not only in sequences of SLG and SRK but also in the location of the S-locus genes. In order to compare the physical loc ation of the S-locus genes in various S haplotypes, we used six class-I S h aplotypes of B. rapa and seven class-I S haplotypes of B. oleracea in this study. DNA gel blot analysis using pulsed-field gel electrophoresis (PFGE) showed that the physical distances between SLG and SRK in B. rapa are signi ficantly shorter than those in B. oleracea and that the sizes of MluI and B ssHII fragments harboring SLG and SRK are less variable within B. rapa than within B, oleracea. We concluded that several large genomic fragments migh t have been inserted into the S-locus region of B. oleracea after allelic d ifferentiation of S-locus genes.