GENETIC-EVIDENCE FOR THE REQUIREMENT OF THE BRASSICA S-LOCUS RECEPTOR KINASE GENE IN THE SELF-INCOMPATIBILITY RESPONSE

In self-incompatible plants, the recognition and subsequent rejection of self-related pollen by the stigma during pollination are genetically controlled by haplotypes of the S-locus complex. We identified two self-compatible Brassica strains that carried nonfunctional S haplotypes and that did not express transcripts of SRK, an S-locus gene that encodes a receptor-like protein kinase. In one of these strains, a deletion generated a null allele of the SRK structural gene. This deleted haplotype exhibited typical interactions when combined with other normal haplotypes in heterozygotes indicating that other functions of the haplotype were retained. The data support a mechanism of self-incompatibility in which activation of the SRK kinase triggers the signalling cascade that culminates in the arrest of incompatible pollen development.