Like most sexually reproducing organisms, plants have mechanisms to select among potential mating partners. This ensures fitness and a suitable level of variation from one generation to the next. In flowering plants, much of this selection occurs at the molecular level, and comes in the form of specific interactions between the pollen (male) and pistil (female) that occur prior to fertilization. Proteins expressed by the pollen and the pistil mediate these interactions. The self-incompatibility system in Nicotiana is a selection system that allows plants to recognize and reject pollen from closely related plants and, thus, serves to avoid inbreeding. The goal of the proposed research is to learn how and where pollen and the pistil proteins interact to allow this selectivity. Pistil factors will be labelled with a fluorescent protein and their uptake and processing in pollen followed. The results will show which internal pollen compartments contain pistil proteins. A previously identified pistil protein, called HT-B, appears to be particularly important for pollen recognition. HT-B is degraded in compatible pollen but it is relatively stable in pollen undergoing rejection. Biochemical experiments are proposed that will determine how the structure of HT-B relates to its function and differential stability in pollen rejection. The results will indicate whether HT-B is associated with specific pollen compartments and suggest how this association might occur. The location of proteins that determine the specificity of pollen rejection and where they interact during the rejection process will also be determined. Together, the results will help explain how mate selection occurs in plants. This knowledge is important for improving agriculture through plant breeding and for understanding natural plant populations. Because the research involves fundamental ideas and techniques in biochemistry and genetics it provides an excellent arena for training at the undergraduate, graduate, and postdoctoral levels.
