A Brassica S locus gene promoter directs sporophytic expression in the anther tapetum of transgenic Arabidopsis

The S locus glycoprotein (SLG) gene of Brassica encodes stigmatic glycoproteins that are implicated in the pollenstigma interaction of self-incompatibility. We have transformed the related plant Arabidopsis thaliana with a chimaeric gene consisting of the promoter region of an SLG gene fused to the reporter gene β-glucuronidase (GUS). In transgenic plants the gene was expressed in two cell types of the flower. In stigmas, the timing and distribution of GUS activity was similar to that previously described for SLG expression in Brassica. In anthers, expression was detected at an earlier stage of flower development with GUS activity restricted to the tapetal cell layer. The novel finding of SLG-promoter activity in the anther supports the hypothesis that sporophytic control of self-incompatibility is a result of SLG-gene expression in the tapetum.