Cell Differentiation and the Plant Cell Cycle

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During the development of multicellular organisms, cell differentiation is tightly coordinated with cell division. In animals, loss of control of cell division leads to cancer. In both plant and animal differentiation, some cell types display a modified cell division cycle where the DNA is replicated without concomitant cell division, thus, increasing nuclear DNA content. This is called endoreplication; in plants, important examples of endoreplicated cell types include cereal endosperm, cotton fibers, and nitrogen-fixing symbiotic nodules in legumes. Although endoreplication is known to be important in these critical systems, its detailed mechanism and regulation remain poorly understood. Previous work using Arabidopsis leaf hairs (trichomes) as a model for cell differentiation demonstrated that the SIAMESE (SIM) gene encodes a cyclin-dependant kinase inhibitor that suppresses mitosis during establishment of endoreplication, and defined a gene family of SIAMESE-RELATED (SMR) genes found in all land plant genomes that may function similarly. The project aims are to better define the biochemical mechanisms through which the SIM protein inhibits cell division, to test hypotheses about how the SIM protein itself is regulated, and to investigate the roles of some of the SMR genes in plant growth and development. By illuminating the mechanisms underlying endoreplication and the coordination of cell division and cell differentiation, the project will advance the understanding of plant growth and development relevant to improvement of both traditional crops and production of biomass for biofuels. Additionally, comparison of plant and animal cell cycle control mechanisms may give useful insights relevant to human disease. Finally, the projected work will play a role in the education of graduate students, undergraduates, and high school students from diverse backgrounds.