Expression level of the SLG gene is not correlated with the self-incompatibility phenotype in the class II S haplotypes of Brassica oleracea.

In Brassica, the S-locus glycoprotein (SLG) gene has been strongly implicated in the self-incompatibility reaction. Several alleles of this locus have been sequenced, and accordingly grouped as class I (corresponding to dominant S-alleles) and class II (recessive). We recently showed that a self-compatible (Sc) line of Brassica oleracea expressed a class II-like SLG (SLG-Sc) gene. Here, we report that the SLG-Sc glycoprotein is electrophoretically and immunochemically very similar to the recessive SLG-S15 glycoprotein, and is similarly expressed in stigmatic papillae. Moreover, by seed yield analysis, we observed that both alleles are associated with a self-compatibility response, in contrast with the other known recessive S haplotypes (S2 and S5). By genomic DNA blot analysis, we show the existence of molecular homologies between the Sc and S15 haplotypes, but demonstrate that they are not identical. On the other hand, we also report that the S2 haplotype expresses very low amounts of SLG glycoproteins, although it exhibits a self-incompatible phenotype. These results strongly question the precise role of the SLG gene in the molecular mechanisms that control the self-incompatibility reaction of Brassica.