AN ARABIDOPSIS MYB HOMOLOG IS INDUCED BY DEHYDRATION STRESS AND ITS GENE-PRODUCT BINDS TO THE CONSERVED MYB RECOGNITION SEQUENCE

An Arabidopsis cDNA (Atmyb2) that contains a sequence that encodes a t ranscription factor, which is a homolog of MYB, was cloned from a cDNA library prepared from dehydrated Arabidopsis rosette plants. A gene ( Atmyb2) corresponding to the Atmyb2 cDNA was also cloned and its nucle otide sequence was determined. RNA gel blot analysis showed that the A tmyb2 mRNA was induced by dehydration and disappeared upon rehydration . The Atmyb2 mRNA also accumulated upon salt stress and with the onset of treatment with abscisic acid. A beta-glucuronidase reporter gene d riven by the Atmyb2 promoter was induced by dehydration and salt stres s in transgenic Arabidopsis plants. These observations indicate that A tmyb2 is responsive to dehydration at the transcriptional level. The p utative protein (ATMYB2) encoded by Atmyb2 has 274 amino acids, a mole cular mass of 32 kD, and a putative DNA binding domain that shows cons iderable homology to plant MYB-related proteins, such as maize C1. A f usion protein that included ATMYB2 was expressed in Escherichia coli, and it bound specifically to oligonucleotides that contained a consens us MYB recognition sequence (TAACTG), such as is found in the simian v irus 40 enhancer and the maize bronze-1 promoter. Binding was sequence specific, as indicated by a gel mobility shift experiment. These resu lts suggest that a MYB-related transcription factor is involved in the regulation of genes that are responsive to water stress in Arabidopsi s.