REGULATION OF GENES THAT ARE INDUCED BY DROUGHT STRESS IN ARABIDOPSIS-THALIANA

Plants respond to drought with physiological and developmental changes. Many plant genes have been shown to be induced by drought stress and function in drought tolerance. We isolated nine independent genes that are responsive to drought in Arabidopsis thaliana and analyzed the structure of their gene products. Sequence analyses of these genes indicate that their gene products may function in protecting cells from dehydration. We also analyzed the expression of these genes under various stress conditions. Some of the drought-responsive genes are induced by plant hormone abscisic acid (ABA), but others are not. There seem to be at least three independent signal transduction pathways between initial drought stress signal and gene expression. Two of the pathways are ABA-dependent, but one is ABA-independent. Protein synthesis is necessary for one of the ABA-dependent pathways. We precisely analyzed the promoter of two drought-inducible Arabidopsis genes, rd29A and rd29B, in transgenic plants, and identified a novel cis-acting element containing 9 bp, TACCGACAT (DRE, Dehydration Responsive Element), that is involved in the ABA-independent response of rd29A to conditions of dehydration or high salt. DRE is also involved in the induction by low temperature, but does not function in the ABA-responsive, slow expression of rd29A. One of myb-related genes, Atmyb2, that is responsive to water stress and abscisic acid (ABA) has been cloned from Arabidopsis. Atmyb2 encodes a transcription factor and binds to conserved MYB recognition sequence. These results suggest that the ABA-mediated induction of drought-inducible genes whose expression requires protein synthesis may be regulated by the ATMYB2 protein.