Role of arabidopsis MYC and MYB homologs in drought- and abscisic acid-regulated gene expression.
In Arabidopsis, the induction of a dehydration-responsive gene, rd22, is mediated by abscisic acid (ABA) and requires protein biosynthesis for ABA-dependent gene expression. Previous experiments established that a 67-bp DNA fragment of the rd22 promoter is sufficient for dehydration- and ABA-induced gene expression and that this DNA fragment contains two closely located putative recognition sites for the basic helix-loop-helix protein MYC and one putative recognition site for MYB. We have carefully analyzed the 67-bp region of the rd22 promoter in transgenic tobacco plants and found that both the first MYC site and the MYB recognition site function as cis-acting elements in the dehydration-induced expression of the rd22 gene. A cDNA encoding a MYC-related DNA binding protein was isolated by DNA-ligand binding screening, using the 67-bp region as a probe, and designated rd22BP1. The rd22BP1 cDNA encodes a 68-kD protein that has a typical DNA binding domain of a basic region helix-loop-helix leucine zipper motif in MYC-related transcription factors. The rd22BP1 protein binds specifically to the first MYC recognition site in the 67-bp fragment. RNA gel blot analysis revealed that transcription of the rd22BP1 gene is induced by dehydration stress and ABA treatment, and its induction precedes that of rd22. We have reported a drought- and ABA-inducible gene that encodes the MYB-related protein ATMYB2. In a transient transactivation experiment using Arabidopsis leaf protoplasts, we demonstrated that both the rd22BP1 and ATMYB2 proteins activate transcription of the rd22 promoter fused to the beta-glucuronidase reporter gene. These results indicate that both the rd22BP1 (MYC) and ATMYB2 (MYB) proteins function as transcriptional activators in the dehydration- and ABA-inducible expression of the rd22 gene.
Abe
H
H
Biological Resources Division, Japan International Research Center for Agricultural Sciences (JIRCAS), Ibaraki, Japan.
Yamaguchi-Shinozaki
K
K
Urao
T
T
Iwasaki
T
T
Hosokawa
D
D
Shinozaki
K
K
D000040:Abscisic Acid / Q000494:pharmacology*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics*; D001483:Base Sequence; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D016259:Genes, myc; D005966:Glucuronidase / Q000235:genetics; D018257:Helix-Loop-Helix Motifs; D008969:Molecular Sequence Data; D009857:Oncogenes; D030821:Plants, Genetically Modified / Q000235:genetics; D011401:Promoter Regions, Genetic; D017386:Sequence Homology, Amino Acid; D015533:Transcriptional Activation
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D000040:Abscisic Acid; D005966:Glucuronidase