Using S-locus deletions to evaluate self-incompatibility candidate genes: an example for a novel anther-expressed gene

A navel gene, designated SPA, was isolated using a differential display strategy designed to target the Brassica self-incompatibility (S) locus for anther-expressed sequences. SPA is genetically and physically linked to the S locus and produces two transcripts expressed predominantly in anthers. SPA alleles exhibit a degree of sequence poly morphism comparable to that characteristic of the S locus glycoprotein and S receptor kinase genes which are known to be required for self-incompatibility in the stigma. Thus, SPA fulfills several of the criteria predicted for a gene that encodes the pollen component of self-incompatibility. However, analysis of an S-locus deletion that encompasses this gene rules out a role for this gene as a determinant of specificity in the self-incompatibility response.