Regulation of Cell Proliferation during Plant Organ Morphogenesis

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0091306Torii Body size of multicellular organisms depends on the coordinated interplay of cell proliferation and differentiation of the developmental program. In higher plants, organ formation occurs throughout the life cycle by continual activity of the shoot meristem. Because plant cells lack motility due to rigid cell walls, spatio-temporal patterns of cell division and cell expansion are thought to ultimately determine plant body size. Although the cell cycle machinery that drives cell division has been extensively studied in plants, little is known about how the machinery acts in the context of growth and development of a plant as a whole. A goal of this proposal is to elucidate the connection between plant morphogenesis and cell proliferation by investigating roles of cell cycle regulators in specifying organ cell numbers, and therefore the organ size. Drs. Torii, Comai, and Roberts have identified eight Arabidopsis genes similar to the mammalian cyclin kinase inhibitor (CKI) p27kip1, which acts as a negative regulator of the cell cycle. Preliminary analyses of the Arabidopsis thaliana CKIs (AtCKI) suggested that mRNA suppression of the AtCKI causes enlargement of mature organs, presumably due to both an enlarged shoot meristem and delayed cessation of the meristematic competence of developing organs. The research in the present project period is intended to: (1) Biochemically characterize the AtCKI, (2) Analyze the relationship between cell proliferation and organogenesis by characterizing plants altered in the AtCKI levels, (3) Examine functional redundancy among different AtCKIs, and (4) Understand interplays between AtCKI-mediated cell proliferation and characterized developmental regulatory pathways. These experiments should provide a novel insight into developmental mechanism controlling plant organ size and define the roles for cell cycle control in plant organogenesis. Moreover, this research should lay the foundation for designing desirable organ sizes through genetic manipulation.