Molecular genetics of self-incompatibility in Brassica napus

Self-incompatibility (SI) is one of the mechanisms evolved by higher plants to promote outbreeding. In Brassica species. SI is controlled sporophytica lly by a single Mendelian genetic locus, the S-locus. Pollen rejection or a cceptance is determined by the parental genotype, and pollen grains carryin g the same allele as that present in the stigma are I-ejected. Among the ge nes identified so far from different S-haplotypes, the S-locus glycoprotein (SLG) and the S-locus receptor kinase (SRK) have been extensively studied. The current model of SI in Brassica postulates that a highly polymorphic p ollen-borne ligand would be specifically recognized by SLG and/or SRK. This would activate a signal transduction pathway leading to rejection of self- pollen. We used a genomic approach in an attempt to identify a putative lig and gene. The S-locus regions of two functional Brassica napus S-haplotypes (910 and A14) were subcloned in Fosmid vectors and sequenced. New transcri ption units were identified by homology searches in the databases, gene pre diction programs and polymerase chain reaction (PCR) amplification. The cur rent study reports the structural features of both S-locus regions and a fu nctional analysis using a transformation-based assay. (C) 2000 Annals of Bo tany Company.