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.
