Cell Differentiation and the Plant Cell Cycle

在多细胞生物的发育过程中，细胞分化与细胞分裂是紧密协调的。在动物身上，失去对细胞分裂的控制会导致癌症。在植物和动物的分化中，一些细胞类型显示出一个修改的细胞分裂周期，其中DNA被复制而没有伴随细胞分裂，因此增加了核DNA含量。这被称为内复制；在植物中，内复制细胞类型的重要例子包括谷物胚乳、棉花纤维和豆科植物的固氮共生根瘤。虽然已知内复制在这些关键系统中很重要，但其详细机制和调控仍然知之甚少。先前使用拟南芥叶毛（毛状体）作为细胞分化模型的研究表明，SIAMESE （SIM）基因编码一种周期蛋白依赖性激酶抑制剂，在内复制建立过程中抑制有丝分裂，并定义了一个在所有陆地植物基因组中发现的SIAMESE相关（SMR）基因家族，其功能可能相似。该项目的目的是更好地确定SIM蛋白抑制细胞分裂的生化机制，验证关于SIM蛋白本身如何被调节的假设，并研究一些SMR基因在植物生长发育中的作用。通过阐明内复制和细胞分裂和细胞分化的协调机制，该项目将促进对植物生长和发育的理解，从而改善传统作物和生物燃料生物质的生产。此外，植物和动物细胞周期控制机制的比较可能提供与人类疾病相关的有用见解。最后，本研究将对不同背景的研究生、本科生和高中生的教育起到一定的作用。

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.