Many plants can recognize and reject their own pollen in order to avoid the deleterious effects of self-fertilization. Current knowledge of pollen recognition systems in plants comes from just two molecular systems. This project will explore a third system, that of the poppy family. This system has several advantages for studying self-recognition including ease of mating-type determination and the availability of in-vitro assays of rejection reactions. The investigators will determine the history of different mating-type alleles at the self-recognition locus. The data will be used to test recent models of the development of self-recognition loci and will provide comparisons with other systems in which the selective forces are the same, but the molecular mechanisms of self-recognition differ.
Self-recognition genes provide stunning examples of extreme genetic variation. The process underlying this variation is selection that continuously favors new or rare types. Selection favoring rarity underlies the diversification of the immune system genes in humans and may be responsible for the maintenance of sex in plants and animals. This study will contribute to our knowledge of the maintenance of variation at these loci which is required to maintain population viability. In addition, this project will provide extensive training for undergraduate and graduate student, including Native Alaskans.
Intellectual Merit: Plant self-incompatibility genes allow hermaphroditic plants to avoid self-fertilization and the consequential problems from inbreeding depression. It is a form of self-recognition, in some ways like the immune system of mammals. In gametophytic self-incompatibility (GSI), pollen cannot fertilize a plant with the same allele. This creates strong frequency dependent selection on self-incompatibility genes, favoring rare mating-type alleles, because pollen carrying rare alleles can fertilize many plants. GSI has evolved independently several times in plants, using different molecular mechanisms. However, our current understanding of GSI comes almost entirely from a single one of these systems, the S-RNase based Solanaceae/Rosaceae system. It is currently not clear what observations from Solanaceae/Rosaceae are general to GSI, and which are influenced by features specific to these taxa. The goal of this project was to compare the diversification patterns of these self-recognition genes in the Papaveraceae system to other self-incompatibility systems where the selective forces are the same, but the molecular mechanism is different. In the Solanaceae/Rosaceae GSI system, many highly divergent S-alleles are maintained within populations. Consistent with this, our results show that divergence among alleles in Papaveraceae is very high, and many S-alleles appear to be maintained within populations. However, our data also point some differences, for instance, transgeneric polymorphisms are common in the Solanaceae/Rosaceae system, but the Papaveraceae system does not offer a strong support for this phenomena. Also, the number of amino acid sites under diversifying selection (candidates for mating-specificity sites) appears to be much smaller than in Solanaceae/Rosaceae. Our research will allow a better, more generalized understanding of the effects of frequency dependent selection on molecular evolution by separating the general properties of molecular evolution of self-recognition systems from the features specific to certain groups of taxa. Broader impacts: The University of Alaska is a U.S. Department ofEducation accredited minority-serving university. During the course of this grant, 1 postdoc, 2 graduate students, and 3 undergraduates have been directly involved in this project, and we have trained an additional 1 postdoc, 4 graduate students, 14 undergraduates and 8 high school students. Bioinformatics scripts have been made available on the internet, which are being used by international researchers.
