Regulation of Cell Proliferation during Plant Organ Morphogenesis

多细胞生物的托里体大小取决于细胞增殖和分化的协调相互作用的发育程序。在高等植物中，器官的形成通过茎分生组织的持续活动在整个生命周期中发生。由于植物细胞由于细胞壁僵硬而缺乏运动性，细胞分裂和细胞扩张的时空模式被认为最终决定了植物体内的大小。虽然驱动细胞分裂的细胞周期机制在植物中得到了广泛的研究，但人们对这些机制如何在整个植物的生长和发育过程中发挥作用知之甚少。这项建议的一个目的是通过研究细胞周期调节因子在指定器官细胞数量和器官大小中的作用来阐明植物形态发生和细胞增殖之间的关系。Torii，Comai和Roberts博士已经确定了8个拟南芥基因，类似于哺乳动物细胞周期蛋白激酶抑制物(CKI)p27kip1，它起到了细胞周期的负调节作用。对拟南芥CKI(AtCKI)的初步分析表明，AtCKI的mRNA抑制导致成熟器官的增大，可能是由于茎分生组织增大和发育中器官的分生能力延迟停止所致。本项目研究的目的是：(1)对AtCKI进行生化表征；(2)通过表征AtCKI水平上的变化来分析细胞增殖和器官发生之间的关系；(3)检测不同AtCKI之间的功能冗余；(4)了解AtCKI介导的细胞增殖和表征发育调控途径之间的相互作用。这些实验将为控制植物器官大小的发育机制提供新的见解，并确定细胞周期控制在植物器官发生中的作用。此外，这项研究将为通过基因操作设计理想的器官大小奠定基础。

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.