| Research Abstract |
Under water deficit conditions, various genes are induced and are thought to function in stress tolerance and response. To understand molecular responses to drougt stress, we cloned about 50 cDNAs for drought-inducib1e genes form Arabidopsis thaliana. These drought-inducible genes are classified into two groups, one is function proteins that are involved in drought tolerance and thc other is regulatory proteins involved in stress response. We analyzed the expression patterns of these drought-inducible genes, and identified at least four independent signal transduction pathways between the initial dehydration signal and gene expression. Two are ABA-dependentand two are ABA-independent.
We identified a cis-acting elerment (DRE,TACCGACAT) involved in one of the ABA-independent gene expression of the rd29A gene in response to dehydration and cold stress. We isolated and analyzed cDNAs (DREB) for DRE binding proteins by yeast two hybrid system. They are classified in tow two subgroups.They e
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ncode DNA binding proteins that contoin a conserved DNA binding motif found in AP2 and EREBP proteins. DREBl genes are induced by low temperature, while DREB2 genes are induced by drought and high salinity. These results indicate that two DREB proteins, DREBl and DREB2, function as transcription factors in two separate signal transduction pathways under low temperature and dehydration, respectively.
The induction of an Arabidopsis drought-inducible genes, rd22, is mediated by ABA,but requires protein biosynthesis for its ABA-dependent expression, A 67-bp region of the rd22 promoter is essential for its ABA-responsive expression, and contains several conserved motifs of DNA binding proteins, such as MYC and MYB,but MYB,but no ABREs. Rccently, a cDNA for a transcription factor MYC homologue was cloned by southwestern method using the 67-bp DNA as a probe, which suggests that drought-inducible MYC homologue may function in the ABA-inducible expression of rd22. These results indicates that drought-or ABA-inducible transcription factor(s) for MYB and MYC function in the ABA-responsive gene expression under drought stress. Less
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