In Vitro and In Vivo Functions of the XET-Related TCH4 Protein

细胞壁是植物细胞的基本结构，控制细胞的形状和完整性，并在信号转导中发挥作用。然而，细胞壁修饰在植物形态发生中的作用在很大程度上仍然未知。修饰细胞壁多糖的蛋白质可能调节细胞壁结构，从而可能在植物形态发生中发挥关键作用。最近，一个拟南芥基因TCH4被证明与木葡聚糖内转糖基化酶（XET）酶密切相关。由于TCH4基因在环境刺激下强烈而快速地表达上调，因此可能存在这种基因表达调控的生理相关性是引发细胞壁修饰，从而引起环境刺激后发生的发育变化。支持的工作重点是研究TCH4基因产物的功能，并确定该蛋白在细胞壁修饰和植物发育中的作用。纯化的TCH4蛋白将检测XET和相关酶的活性。由于已经提出XET可能导致细胞壁松动和细胞扩增，因此将测试TCH4是否能够引起离体植物下胚轴段的延伸。将产生过表达或低表达TCH4基因的转基因植株，以确定改变TCH4基因在体内的表达对生理和发育的影响。针对TCH4基因产物的特异性抗体将用于在植物组织发育过程中定位该蛋白，并确定其亚细胞位置。最后，由于TCH4是一个密切相关的基因家族的成员，因此将开始对其他家族成员的功能和调控进行类似的详细分析。

9418750 Braam The cell wall is a fundamental structure in plant cells that controls cellular shape and integrity and plays a role in signal transduction. Yet the involvement of cell wall modifications in plant morphogenesis remains largely unknown. Proteins that modify cell wall polysaccharides would be expected to regulate cell wall structure and thus likely play critical roles in plant morphogenesis. Recently, an Arabidopsis gene, TCH4, has been shown to be significantly related to xyloglucan endotransglycosylase (XET) enzymes. Because the TCH4 gene is strongly and rapidly upregulated in expression in response to environmental stimuli, the possibility exists that the physilogical relevance of this regulation of gene expression is to elicit cell wall modifications and thus the developmental changes that occur following environmental stimulation. The focus of the work supported is to investigate the function(s) of the TCH4 gene product and to ascertain the roles of this protein in cell wall modifications and plant development. Purified TCH4 protein will be assayed for XET and related enzyme activities. Because it has been proposed that XET may cause cell wall loosening and cell expansion, TCH4 will be tested for the ability to cause extension of isolated plant hypocotyl segments. Transgenic plants that over-express or under-express the TCH4 gene will be generated to determine the physiological and developmental effects of altering TCH4 expression in vivo. Antibodies specific for the TCH4 gene product will be used to localize the protein in plant tissues during development, and to determine its subcellular location. Finally, because TCH4 is a member of a closely related gene family, similar detailed analyses of the functions and regulation of the other family members will be initiated.