Two distantly related plant families, the Solanaceae (potato family) and Rosaceae (rose family) use the same molecular method to reject self pollen. This project will examine diversification at the self incompatibility (S-) locus in the Rosaceae to test hypotheses about differences in S-allele evolution in the two families. Preliminary data indicate that alleles in the Rosaceae are quite young and that non-overlapping sets of alleles occur in the two subfamilies investigated. This stands in stark contrast to the lack of turnover and ancient alleles seen in the Solanaceae. This project will determine if these differences generally hold or are peculiar to the groups of Rosaceae that have been sampled and evaluate equilibrium and non-equilibrium hypotheses to explain family-level differences. This project will also use sequence and gene structure information to determine whether use RNases for self incompatibility in these two families is due to common ancestry or parallel evolution.
Loci involved in self-nonself recognition exhibit the highest levels of genetic variability known. Examples include the self-incompatibility loci of flowering plants, fungi, and clonal marine invertebrates, and the disease fighting major histocompatiblity loci (MHC) of humans and other vertebrates. Extreme variability is due to the types of selection, generally called balancing selection, that act on such genes. Understanding the evolution these genes is important for many fields. First, the much greater time depth of variation allows historical inference that reaches farther back in time than is possible when using other genes. Second, analysis of diversification patterns at these genes provides information on the selective forces that drive their evolution. Third, examination of patterns of selection at the molecular level provides insight into as yet poorly understood aspects of the molecular basis of self recognition.
