Analysis of the self-incompatibility locus of Brassica using plant transformation and comparative mapping.

摘要

Brassica crops encompass many diverse types of plants. Brassicas are grown as vegetables, as sources of oils and for fodder. Many species of Brassica contain a genetic barrier to self-fertilization termed self-incompatibility. The genetic determinants of the self-incompatible response are encoded at the S locus.; The S locus is a complex locus that contains all functions required for self-incompatibility in stigma and pollen. Two S-locus genes required for self-incompatibility have been characterized. The S. Locus (SLG) gene encodes a secreted glycoprotein. The S-locus Receptor Kinase (SRK) gene encodes a plasma membrane protein kinase having an extracellular S-receptor domain that is highly similar to SLG.; To gain a further understanding of the requirement of SRK in SI and to set the stage for future structure-function analysis of the S-receptor domain of SRK, chimeric SRK genes were transformed into the self-compatible {dollar}Ssb{lcub}f1{rcub}Ssb{lcub}f1{rcub}{dollar} strain which carries a null SRK allele. Transgene-induced silencing of the endogenous {dollar}SLGsb{lcub}f1{rcub}{dollar} gene was observed in a large percentage of the transformants. Suppression was specific for the {dollar}SLGsb{lcub}f1{rcub}{dollar} gene and did not affect other members of the S gene family. In some of the selfed progeny of the original transformants, the endogenous {dollar}SLGsb{lcub}f1{rcub}{dollar} gene remained suppressed after the removal of the transgene by segregation. In one family, the suppression of {dollar}SLGsb{lcub}f1{rcub}{dollar} was likely due to the methylation of the promoter of the gene. A different mechanism may also cause suppression as methylation of the promoter was not established in another family also showing suppression. This suppression phenomenon limits the ability of using a transgenic approach in the study of self-incompatibility.; A comparative mapping study of specific genomic regions of Arabidopsis and Brassica was undertaken to generate molecular markers that would saturate the S locus and perhaps help in the future isolation of novel genes required for self-incompatibility. Using Arabidopsis YAC and BAC clones containing molecular markers which flank SLG and SRK, I isolated clones which extend our knowledge of the S locus. One marker was found to identify one edge of the locus.