Collaborative research: The Evolutionary Genetics of Pollen-Pistil Incompatibility and Reproductive Isolation in Zea mays

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Because hybridization between plant species often results in offspring with reduced fitness, it remains a mystery why hybridization persists and is even fairly common in nature. To address this fundamental question, this research investigates genes that control the mating compatibility between individuals. These genes are distributed differently among populations of corn and its wild ancestor, teosinte. Although these are parts of the same species, Zea mays, they represent distinct subspecies and some populations of these subspecies interbreed easily and others do not. This system serves as a valuable genetic model to investigate the problem of hybridization and especially an overlooked conflict between males and females of the plant species. While females that reject pollen from the wrong species avoid producing low quality offspring (avoiding hybridization), males with pollen that can fertilize, and produce even low quality offspring with closely related species or subspecies will have higher fitness (promoting hybridization). By identifying and studying the genes underlying mating compatibility in this well-studied and economically important plant, this project may determine the forces that allow or prevent species from avoiding hybridization. This research combines computational, mathematical, and genetic approaches to address these questions. The research team will train undergraduates, graduate students, and postdoctoral researchers in California and Minnesota. They will also develop classroom materials for K-12 students in California and offer Biomath summer camps for high school girls in Minnesota.This research addresses how interactions between the pollen and style shape the ability of a plant to reject pollen from the wrong species. The project also addresses how pollen may overcome this barrier. The work begins with a population genetic model of this process, and asks which parameters allow for females to effectively reject pollen from another subspecies, and which parameters allow pollen to overcome this barrier. A second component of the work involves the fine mapping of one of the three gametophyte factors that modulate cross compatibility between populations of Zea mays subspecies so that the DNA sequence context around all three gametophyte factors is known. Researchers will then conduct a series of genetic crosses to identify the frequency of alternative alleles at the gametophyte factor loci in different sympatric maize and mexicana-type teosinte populations in the Mexican highlands. Finally, these alleles will be sequenced, allowing the researchers to evaluate the predictions of their mathematical model.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.