RESUMEN
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.
Asunto(s)
Brassica/genética , Mapeo Cromosómico , Glicoproteínas/genética , Proteínas de Plantas/genética , Proteínas Quinasas/genética , Secuencia de Aminoácidos , Secuencia de Bases , Brassica/fisiología , Cruzamientos Genéticos , ADN de Plantas/genética , ADN de Plantas/aislamiento & purificación , Ligamiento Genético , Biblioteca Genómica , Glicoproteínas/biosíntesis , Datos de Secuencia Molecular , Proteínas de Plantas/biosíntesis , Reacción en Cadena de la Polimerasa , Proteínas Quinasas/biosíntesis , Técnica del ADN Polimorfo Amplificado AleatorioRESUMEN
An S-receptor kinase (SRK) gene associated with self-incompatibility in a Brassica napus subsp. oleifera line has been characterized. The SRK-A14 cDNA shows the highest levels of homology in the 5' end to the SLG-A14 cDNA present at the same locus. RNA blot analysis shows that the SRK-A14 gene is expressed predominantly in the pistil, and at lower levels in the anthers. The predicted amino acid sequences from the extracellular domain of the SRK-A14 gene and three other SRK genes were compared. The different SRK extracellular domains were for the most part very similar, with the exception of two variable regions containing a high level of amino acid alterations. These extracellular domains also contain a region of similarity to the immunoglobulin domains present in members of the immunoglobulin superfamily. These findings may define regions of the SRK protein that are necessary for interactions between SRK and other proteins.
Asunto(s)
Brassica/enzimología , Brassica/genética , Genes de Plantas , Proteínas Quinasas/genética , Secuencia de Aminoácidos , Secuencia de Bases , Clonación Molecular , ADN de Plantas/análisis , Datos de Secuencia Molecular , Proteínas de Plantas , Reacción en Cadena de la Polimerasa , Homología de Secuencia de AminoácidoRESUMEN
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 A10 allele did not segregate with self-incompatibility in crosses involving other self-incompatible B. napus lines. The SLG-A10 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-A10 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-A10 cDNA showed that it was very similar to other S locus receptor kinase genes and was expressed predominantly in the stigma. However, a 1-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 B. oleracea S allele based on its segregation pattern with the B. oleracea S24 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.