Genomic organization of the Papaver rhoeas self-incompatibility S1 locus

The self‐incompatibility (SI) response in Papaver rhoeas depends upon the cognate interaction between a pollen‐expressed receptor and a stigmatically expressed ligand. The genes encoding these components are situated within the S‐locus. In order for SI to be maintained, the genes encoded by the S‐locus must be co‐inherited with no recombination between them. Several hypotheses, including sequence heterogeneity and chromosomal position, have been put forward to explain the maintenance of the S‐locus in the SI systems of the Brassicaceae and the Solanaceae. A region of the Papaver rhoeas genome encompassing part of the self‐incompatibility S1 locus has been cloned and sequenced. The clone contains the gene encoding the stigmatic component of the response, but does not contain a putative pollen S‐gene. The sequence surrounding the S1 gene contains several diverse repetitive DNA elements. As such, the P. rhoeas S‐locus bears similarities to the S‐loci of other SI systems. An attempt to localize the P. rhoeas S‐locus using fluorescence in situ hybridization (FISH) has also been made. The potential relevance of the findings to mechanisms of recombination suppression is discussed.