3 MEMBERS OF THE S-MULTIGENE FAMILY ARE LINKED TO THE S-LOCUS OF BRASSICA

Two self-incompatibility genes in Brassica, SLG and SRK (SLG encodes a glycoprotein; SRK encodes a receptor-like kinase), are included in th e S multigene family. Products of members of the S multigene family ha ve an SLG-like domain (S domain) in common, which may function as a re ceptor. In this study, three clustered members of the S multigene fami ly, BcRK1, BcRL1 and BcSL1, were characterized. BcRK1 is a putative fu nctional receptor kinase gene expressed in leaves, flower buds and sti gmas, while BcRL1 and BcSL1 are considered to be pseudogenes because d eletions causing frameshifts were identified in these sequences. Seque nce and expression pattern of BcRK1 were most similar to those of the Arabidopsis receptor-like kinase gene ARK1, indicating that BcRK1 migh t have a function similar to that of ARK1, in processes such as cell e xpansion or plant growth. Interestingly, the region containing BcRK1, BcRL1 and BcSL1 is genetically linked to the S locus and the physical distance between SLG, SRK and the three S-related genes was estimated to be less than 610 kb. Thus the genes associated with self-incompatib ility exist within a cluster of S-like genes in the genome of Brassica .