S locus glycoprotein (SLG) and S locus receptor kinase (SRK) cDNAs were isolated from an S allele present in a number of self-compatible Brassica napus lines. This Aí0 allele did not segregate with self-incompatibility in crosses involving other self-incompatible B. napus lines. The SLG-Aí0 cDNA was found to contain an intact open reading frame and was predicted to encode an SLG protein with sequence similarities to those previously associated with phenotypically strong self-incompatibility reactions. SLG-Aí0 transcripts were detected in the developing stigma at steady state levels even higher than those detected for SLG alleles linked with self-incompatibility. Analysis of the corresponding SRK-Aí0 cDNA showed that it was very similar to other S locus receptor kinase genes and was expressed predominantly in the stigma.However, a l-bp deletion was detected in the SRK gene toward the 3' end of the SLG homology domain. This deletion would lead to premature termination of translation and'the production of a truncated SRK protein. The A10 allele was determined to represent a R oleracea S allele based on its segregation pattern with the R oleracea SZ4 allele when both these alleles were present in the same B. napus background. These results suggest that a functional SRK gene is required for Brassica self-incompatibility.

S locus glycoprotein (SLG) and S locus receptor kinase (SRK) cDNAs were isolated from an S allele present in a number of self-compatible Brassica napus lines. This Aí0 allele did not segregate with self-incompatibility in crosses involving other self-incompatible B. napus lines. The SLG-Aí0 cDNA was found to contain an intact open reading frame and was predicted to encode an SLG protein with sequence similarities to those previously associated with phenotypically strong self-incompatibility reactions. SLG-Aí0 transcripts were detected in the developing stigma at steady state levels even higher than those detected for SLG alleles linked with self-incompatibility. Analysis of the corresponding SRK-Aí0 cDNA showed that it was very similar to other S locus receptor kinase genes and was expressed predominantly in the stigma.However, a l-bp deletion was detected in the SRK gene toward the 3' end of the SLG homology domain. This deletion would lead to premature termination of translation and'the production of a truncated SRK protein. The A10 allele was determined to represent a R oleracea S allele based on its segregation pattern with the R oleracea SZ4 allele when both these alleles were present in the same B. napus background. These results suggest that a functional SRK gene is required for Brassica self-incompatibility.

In Brassica species, self-incompatibility has been mapped genetically to a single chromosomal location. In this region, there are two closely linked genes coding for the S locus glycoprotein (SLG) and S locus receptor kinase (SRK). They appear to comprise the pistil component of the self-incompatibility reaction. SLG and SRK are thought to recognize an unknown pollen component on the incompatible pollen, and the gene encoding this pollen component must also be linked to the SLG and SRK genes. To further our understanding of self-incompatibility, the chromosomal region carrying the SLG and SRK genes has been studied. The physical region between the SLG-910 and the SRK-910 genes in the Brassica napus W1 line was cloned, and a search for genes expressed in the anther revealed two additional S locus genes located downstream of the SLG-910 gene. Because these two genes are novel and are conserved at other S alleles, we designated them as SLL1 and SLL2 (for S locus-linked genes 1 and 2, respectively). The SLL1 gene is S locus specific, whereas the SLL2 gene is not only present at the S locus but is also present in other parts of the genomes in both self-incompatible and self-compatible Brassica ssp lines. Expression of the SLL1 gene is only detectable in anthers of self-incompatible plants and is developmentally regulated during anther development, whereas the SLL2 gene is expressed in anthers and stigmas in both self-incompatible and self-compatible plants, with the highest levels of expression occurring in the stigmas. Although SLL1 and SLL2 are linked to the S locus region, it is not clear whether these genes function in self-incompatibility or serve some other cellular roles in pollen-pistil functions.

In Brassica species, self-incompatibility has been mapped genetically to a single chromosomal location. In this region, there are two closely linked genes coding for the S locus glycoprotein (SLG) and S locus receptor kinase (SRK). They appear to comprise the pistil component of the self-incompatibility reaction. SLG and SRK are thought to recognize an unknown pollen component on the incompatible pollen, and the gene encoding this pollen component must also be linked to the SLG and SRK genes. To further our understanding of self-incompatibility, the chromosomal region carrying the SLG and SRK genes has been studied. The physical region between the SLG-910 and the SRK-910 genes in the Brassica napus W1 line was cloned, and a search for genes expressed in the anther revealed two additional S locus genes located downstream of the SLG-910 gene. Because these two genes are novel and are conserved at other S alleles, we designated them as SLL1 and SLL2 (for S locus-linked genes 1 and 2, respectively). The SLL1 gene is S locus specific, whereas the SLL2 gene is not only present at the S locus but is also present in other parts of the genomes in both self-incompatible and self-compatible Brassica ssp lines. Expression of the SLL1 gene is only detectable in anthers of self-incompatible plants and is developmentally regulated during anther development, whereas the SLL2 gene is expressed in anthers and stigmas in both self-incompatible and self-compatible plants, with the highest levels of expression occurring in the stigmas. Although SLL1 and SLL2 are linked to the S locus region, it is not clear whether these genes function in self-incompatibility or serve some other cellular roles in pollen-pistil functions.

The self-incompatible (SI) Brassica napus line W1, which carries the 910 S allele, was transformed with an inactive copy of the 910 S locus receptor kinase ( SRK ) gene. Two transformed lines were analyzed based on their heritable ability to set self-seed. The first line was virtually completely self-compatible (SC), and reciprocal pollinations with the original W1 line demonstrated that only the stigma side of the SI phenotype was altered. An analysis of the expression of endogenous SRK-910 demonstrated that the mechanism of transgene action is via gene suppression. Furthermore, the expression of the S locus glycoprotein gene present in the 910 allele ( SLG-910 ), SLG-A10 , which is derived from a nonfunctional S allele, and an S locus-related gene were also suppressed. When the transgene was crossed into another SI line carrying the A14 S allele, it was also capable of suppressing the expression of the endogenous genes and of making this line SC. The second transgenic line studied was only partly SC. In this case as well, only the stigma phenotype was affected, although no gene suppression was detected for endogenous SRK-910 or SLG-910 . In this line, the expression of the transgene most likely was causing the change in phenotype, and no effect was observed when this transgene was crossed into the other SI line. Therefore, this work reinforces the hypothesis that the SRK gene is required, but only for the stigma side of the SI phenotype, and that a single transgene can alter the SI phenotype of more than one S allele.