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 imp licated in the self-incompatibility reaction. Several alleles of this locus have been sequenced, and accordingly grouped as class I (corresp onding to dominant S-alleles) and class II (recessive). We recently sh owed 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 glyc oprotein is electrophoretically and immunochemically very similar to t he recessive SLG-S15 glycoprotein, and is similarly expressed in stigm atic papillae. Moreover, by seed yield analysis, eve observe that both alleles are associated with a self-compatibility response, in contras t with the other known recessive S haplotypes (S2 and S5). By genomic DNA blot analysis, we show the existence of molecular homologies betwe en the Sc and S15 haplotypes, but demonstrate that they are not identi cal. On the other hand, we also report that the S2 haplotype expresses very low amounts of SLG glycoproteins, although it exhibits a self-in compatible phenotype. These results strongly question the precise role of the SLG gene in the molecular mechanisms that control the self-inc ompatibility reaction of Brassica.