Many investigators have observed alterations in gene expression in response to drought stress. A number of these genes have been cloned, sequenced, and based on derived protein sequence comparisons, functions or activities for only a new of these stress induced sequences have been proposed. Genes that confer drought resistance have not been identified or isolated. It is our long-term goal to identify the genes and understand the molecular basis for the drought resistance exhibited by selected plants. In the short term, we propose to describe the genes and gene products induced by drought-stress in roots in the drought-resistance tomato species, Lycopersicon chilense. Several strategies have been employed to identify transcripts which are differentially expressed in L. chilense in response to drought. A cDNA library containing sequences expressed in roots of drought-stressed L. chilense has been screened, and one root-specific and drought-induced clone has been identified,m pCRW-1. A second approach has been to use differential display reverse transcriptase-PCR (DDRT-PCR). A DDRT-PCR based comparison of RNA from tomato and L. chilense roots from control and drought-stressed plants has been initiated and a number of differentially expressed sequences have been identified. DNA sequence information will be generated for selected clones and compared with sequences in databases. The abundance of drought-induced and drought-repressed transcripts will be determined on a variety of cell types during a drought cycle. Transgenic plants will be regenerated with constructs designed to study the promoters of drought responsive sequences as well as sense and antisense versions of the drought responsive genes to test the function of the gene product. Students trained in this research program will contribute information about the structure and sequence of differentially expressed genes, about the nature of the cis-elements which confer the environmental responsiveness on the genes, and the interaction of developmental and environmental control on the expression of a set of genes.
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