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

Abstract

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.

The S15 Self-Incompatibility Haplotype in Brassica oleracea Includes Three S Gene Family Members Expressed in Stigmas

“…present but significantly rearranged in) the S 2 haplotype. Gaude et al (1995) have shown that the S 2 homozygous line expresses a very low level of SLG, whereas SLG levels are significantly higher and comparable with those of S 15 in the S 5 homozygous line. Figure 4 shows that in the S 15 haplotype, SLGA is strongly expressed and accounts for 79.5% of stigma SLG, whereas SLGB only encodes 20.5%.…”

Self-Incompatibility in the Genus Arabidopsis: Characterization of the S Locus in the Outcrossing A. lyrata and Its Autogamous Relative A. thaliana

“…SLG, which apparently was formed by a duplication of the SRK gene (Tantikanjana et al, 1993), is found in Brassica and Raphanus spp (Sakamoto et al, 1998). It occurs in tight genetic and physical linkage to the SRK and SCR genes and is expressed at high levels in plants homozygous for most Brassica S haplotypes, but it is absent (Okazaki et al, 1999) or expressed at low levels (Tantikanjana et al, 1993(Tantikanjana et al, , 1996Gaude et al, 1995;Cabrillac et al, 1999) in plants homozygous for a few S haplotypes. An SRKb-related sequence that may be genetically linked to the S locus was detected on DNA gel blots of A. lyrata Sa and Sb homozygotes.…”

Diversification and Alteration of Recognition Specificity of the Pollen Ligand SP11/SCR in Self-Incompatibility of Brassica and Raphanus[W]

“…The pollen-pistil recognition takes place by the interaction between membrane-spanning Ser-Thr protein kinase in the stigma, i.e., S-locus receptor kinase (Stein et al, 1991;Takasaki et al, 2000), and low-molecular weight Cys-rich protein in pollen, i.e., S-locus protein 11(SP11)/S-locus Cys-rich protein (SCR) (Schopfer et al, 1999;Suzuki et al, 1999). The genes encoding these molecules, i.e., SRK and SP11/SCR (referred to as SP11 hereafter), are located in the S locus, and another molecule encoded in the S locus is S-locus glycoprotein (SLG), the function of which in self-incompatibility is still controversial (Gaude et al, 1995;Okazaki et al, 1999;Dixit et al, 2000;Suzuki et al, 2000;Takasaki et al, 2000;Silva et al, 2001). The alleles of SRK, SP11, and SLG are transmitted to the progeny as one set named S haplotype.…”