Milestones identifying self-incompatibility genes in Brassica species: From old stories to new findings

Self-incompatibility (SI) in Brassica species is an elaborate system preventing self-fertilisation. It is important for high-quality seed production in Brassica vegetables, such as cabbage, turnip and Chinese cabbage. In classical genetics, Brassica SI is sporophytically controlled by a single S-locus with multiple alleles. This concept of the S-locus enabled us to beginmolecular studies to determine how the SI system is regulated. Through vigorous molecular analysis by research groupsworldwide, female and male S determinants were identified as a receptor-type protein kinase (SRK) and its ligand (SP11/SCR). In this chapter, we highlight six milestones, which are historically important findings in Brassica SI research, especially with respect to identification of genes regulating the recognition of self-pollen.