The emerging complexity of self-incompatibility (S-) loci

A complex picture of S-loci is beginning to emerge from recent studies of t he S-locus of RNase-based gametophytic self-incompatibility displayed by th e Rosaceae, Solanaceae, and Scrophulariaceae, and of the S-locus of the typ e of sporophytic self-incompatibility displayed by the Brassicaceae. It now appears that not only do these S-loci contain two separate genes, one cont rolling pollen function and the other controlling pistil function in self-i ncompatibility interactions, but also many other genes whose functions are largely unknown. The implications of these recent findings for the study of the mechanisms of self-incompatibililty interactions and evolution of the self-incompatibility systems are discussed.