Flowering plants limit self-fertilization and maintain genetic diversity by a number of mechanisms, ranging from simple physical barriers to complex interactions between components of the pistil and pollen. In plants that posses self-incompatibility systems, self-pollen is distinguished from pollen of genetically unrelated origin in the stigma or style of the pistil. Following the recognition of the presence of self-pollen, the development of self-related pollen grains, but not of genetically-distinct grains, s halted. Although the mechanism of self-recognition is not yet known, a chromosomal location, the S locus, has been shown from genetic crosses to encode the putative pistil and pollen elements that interact in this recognition process. This research will determine: whether a specific region of these genes is a" master switch" which confers specific expressed in the sigma and style of the flower, whether specific DNA binding proteins regulate these genes, and which pollen products interact with proteins coded for by these genes.
