Expression of a self-incompatibility gene in a self-compatible line of Brassica oleracea

In cruciferous plants, self-pollination is prevented by the action of genes situated at the self-incompatibility locus or S-locus. The self-incompatibility reaction is associated with expression of stigma glycoproteins encoded by the S-locus glycoprotein (SLG) gene. Only a few cases of self-compatible plants derived from self-incompatible lines in the crucifer Brassica have been reported. In these cases, self-compatibility was generally ascribed to the action of single genes unlinked to the S-locus. In contrast, we report here a line of Brassica oleracea var acephala with a self-compatible phenotype linked to the S-locus. By means of both biochemical and immunochemical analyses, we showed that this self-compatible (Sc) line nonetheless possesses stigmatic SLGs (SLG-Sc) that are expressed with a similar spatial and temporal pattern to that described for the SLGs of self-incompatible Brassica plants. Moreover, the SLG-Sc products segregate with the self-compatibility phenotype in F2 progeny, suggesting that changes at the S-locus may be responsible for the occurrence of the self-compatibility character. A cDNA clone encoding the SLG-Sc product was isolated, and the deduced amino acid sequence showed this glycoprotein to be highly homologous to the pollen recessive S2 allele glycoprotein. Hence, self-compatibility in this Brassica Sc line correlates with the expression of a pollen recessive-like S allele in the stigma.