Arabidopsis 2010: Functional Analysis of Pollen Exine Assembly

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This project will identify genes required to construct the outer pollen wall (exine). The unparalleled strength and chemical resistance of exine is important for pollen survival. This wall also plays an important role in interactions between male and female cells: exine is required for the species-specific adhesion that takes place between pollen and the female organs of the flowers. Exine is made of sporopollenin, an unusually strong, chemically inert and distinctively patterned biopolymer that may prove useful for the materials science industry. Thus, its importance in pollination, implications for polymer chemistry, and utility as a contact adhesive make an understanding of its composition a high priority. The inert and irregular nature of exine has confounded chemical analysis, but recent Arabidopsis genetic surveys are more promising, revealing genes and pathways required for exine structure and function. The work of the Preuss, Sumner, Edlund, and Swanson labs will extend these efforts. This project addresses the 2010 program goal of functional analysis of every Arabidopsis gene. It will assess the role of specific genes in exine assembly, patterning and adhesion, and will sort these genes into genetic and metabolic pathways. Arabidopsis genes required for establishing normal exine morphology will be defined by visually characterizing ~250 insertions in candidate genes, as well as by performing a large-scale screen for novel mutants. The targeted genes are selected among a) biosynthetic pathways previously implicated by chemical or genetic analyses as playing a role in exine synthesis; b) pathways with an unresolved role in exine synthesis; c) genes resembling those with a known function in exine development; d) genes, whose expression pattern indicates they are likely active in anthers during pollen development. The genes under study and progress of the research will be available at http://preuss.bsd.uchicago.edu/nsf2010.html. Data will be released generally on a semi-annual basis. For each of the mutants identified, microscopic and biochemical assays will be employed to characterize the roles of the mutated genes. Genetic and biochemical networks will then be clarified through characterizing the timing of exine gene expression, examining metabolite accumulation during pollen development, and analyzing double mutants. This work will impact multiple disciplines, improving the understanding of 1) genes that mediate pollination and crop breeding, 2) evolutionary control over exine diversity and plant speciation, 3) biopolymer self-assembly to allow investigators to recapitulate enzymatic steps of exine development in vitro, ultimately resulting in designing exine walls with desired characteristics, 4) exine moieties that contribute to pollen adhesion, possibly allowing the synthesis of highly specific contact adhesives, 5) 250 genes that could play a role in exine development. Education and personnel training will be an integral part of this project. Two technicians and at least 4 undergraduates (including 2 from the primarily undergraduate institutions - Spelman and Valparaiso) will be trained. Students, including those historically underrepresented in science, will have an opportunity for summer research, developing their experience in planning and performing experiments and presenting their work at research conferences. Their mentors will generate information to incorporate in their laboratories and courses. In addition, postdoctoral fellows will be trained in research and mentoring via supervising technicians and undergraduates, enabling transitions to independent careers.