COLLABORATIVE: Functional Analysis of Arabidopsis Formins, a Family of Actin-Nucleating Proteins

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Intellectual Merit: Actin microfilaments are critical cytoskeletal structures in all eukaryotes. The rate-limiting step in the formation of actin microfilaments is the polymerization of the first two to three monomeric actin protein molecules, known as actin nucleation. Formins are one of two known families of actin-nucleating proteins. Plant formins share similarity with their counterparts from other organisms in their actin-nucleating activity domain, but a large number of them (referred to as Group I plant formins) have the plant-unique feature of having a potentially glycosylated extracellular domain and a transmembrane domain that anchor the cytosolic actin-nucleating domain to the cell surface. This project aims to determine the functional roles of 3 group I formins from Arabidopsis, the pollen-specific AFH3, the pollen-, endosperm- and vegetative cell-expressed AFH5, and the root meristem-expressed AFH6, in plant growth and development. As group I formins, these AFHs serve as perfect candidates for mediating extracellular stimuli directly to the actin cytoskeleton, in a manner analogous to the function of integrins of animal cells. Drs. Cheung, Wu and Kieliszewski plan to elucidate the functional roles for these Group I AFHs in plant growth and development through a combination of genetic and cell biological analyses. The glycosylation properties of selected group I extracellular domains and the functional significance of the extracellular domains for these three AFHs (and that of AFH1, a prototypical and thus far the best-characterized plant formin) will be examined. Dr. Cheung and her colleagues will also begin efforts to identify proteins that interact with AFH3 and AFH5, which should lead to elucidation of the protein networks that underlie the regulation and functions of these plant formins. Broader Impacts: For resource development, Dr. Cheung and her colleagues will provide constructs, seeds and antibodies to the community. The PIs routinely host and train postdoctoral, graduate and undergraduate students in their laboratories, and plan to continue to do so in the context of this project. Since 1997, Dr. Cheung has mentored approximately 40 undergraduates, including several from unrepresented ethnic groups, and there are currently undergraduates participating in on-going efforts related to the project. Dr. Kieliszewski also consistently supervises undergraduates in her laboratory. Many of these undergraduates have gone on to graduate school in the sciences. Besides the PIs themselves, postdocs and senior graduate students in the Cheung and Kieliszewski laboratories all contribute to the direct training of undergraduates, therefore providing them with mentoring and teaching experience in preparation for their own future career development. Overall, this research project will provide a broad spectrum of training areas on different levels of sophistication suitable for students at the undergraduate, graduate and postdoctoral level.