Role of Arabidopsis MYC and MYB Homologs in Drought-

The Plant Cell, Vol. 9, 1859-1 868, October 1997 O 1997 American Society of Plant Physiologists

Role of Arabidopsis MYC and MYB Homologs in Droughtand Abscisic Acid-Regulated Gene ExpressionHiroshi Abe,albKazuko Yamaguchi-Shinozaki,all Takeshi Urao,a Toshisuke lwasaki,CDaijiro Hosokawa,b and Kazuo ShinozakiCa Biological Resources Division, Japan lnternational Research Center for Agricultura1 Sciences (JIRCAS), Ministry of Agriculture, Forestry and Fisheries, 1-2 Ohwashi, Tsukuba, lbaraki 305, Japan bDepartment of Applied Biological Sciences, Tokyo University of Agriculture and Technology, Fuchu 183, Japan Laboratory of Plant Molecular Biology, Tsukuba Life Science Center, lnstitute of Physical and Chemical Research (RIKEN), 3-1-1 Koyadai, Tsukuba, lbaraki 305, Japan

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 dehydrationinduced 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 rnotif in MYC-related transcription factors. The rd22BP1 protein binds specifically t o the first MYC recognition site in the 67-bp fragment. RNA gel blot analysis revealed that transcription of the rd226Pí 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 ATMYBS. In a transient transactivation experiment using Arabidopsis leaf protoplasts, we demonstrated that b o t h the rd22BP1 and ATMYB2 proteins activate transcription of the rd22 promoter fused t o the P-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.

INTRODUCTION

Plants respond to environmental stresses with a number of physiological and developmental changes. Drought stress is one condition that affects almost all plant functions, including growth and development. Plant cells sense the loss of water during drought conditions, and a stress signal is then transduced to the nuclei via as yet unknown pathways. This leads to the exp

ression of many genes that function in drought tolerance or drought response. The plant hormone abscisic acid (ABA) is produced under water-deficit conditions and is instrumental in the development of tolerance against drought. Recently, a number of genes have been described that respond to drought at the transcriptional leve1 (reviewed in lngram and Bartels, 1996; Shinozaki and Yamaguchi-Shinozaki, 1996;

'To whom correspondence should be addressed. E-mail kazukoys

@jircas.affrc.go.jp;fax 81-298-38-6643.

Bray, 1997). Most of the drought-induced genes studied to date are also induced by ABA. It appears that dehydration triggers the production of ABA, which in turn induces various genes. cis- and trans-acting factors involved in ABAinduced gene expression have been analyzed (reviewed in Chandler and Robertson, 1994; lngram and Bartels, 1996; Shinozaki and Yamaguchi-Shinozaki, 1996; Bray, 1997). A conserved sequence, PyACGTGGC, has been reported to function as an ABA-responsive element (ABRE) in many ABA-responsive genes (Guiltinan et al., 1990; Mundy et al., 1990; Yamaguchi-Shinozaki et al., 1990). cDNAs encoding DNA binding proteins that specifically bind to the ABRE have been cloned and are shown to contain the basic region leucine zipper (bZIP) structure (Guiltinan et al., 1990). Recently, coupling elements have been shown to be required to specify the function of ABRE, constituting an ABA-responsive complex (Shen et al., 1996).

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Analyses of drought-induced genes indicate the existence of ABA-independent as well as ABA-dependent signal transduction cascades between the initial signal of water deficit and the expression of specific genes (reviewed in lngram and Bartels, 1996; Shinozaki and Yamaguchi-Shinozaki, 1996; Bray, 1997). The ABA-independent expression of genes has been analyzed extensively as well. A novel cis-acting element, designated a dehydration-responsive element, which contains the sequence TACCGACAT, has been identified as a cis-acting element involved in ABA-independent gene expression under drought, high-salt, and low-temperature conditions (Yamaguchi-Shinozaki and Shinozaki, 1994). The core CCGAC sequence has been found in the promoter regions of many cold-inducible genes and designated as the C repeat or low-temperature-responsive element (Baker et al., 1994; Jiang et al., 1996). The existence of multiple signal transduction cascades has been suggested between the perception of the initial signal of water deficit and the expression of genes (reviewed in Shinozaki and YamaguchiShinozaki, 1996). We have shown that the expression of one of the dehydration-responsive genes, rd22, is induced by the application of exogenous ABA in Arabidopsis (Yamaguchi-Shinozaki and Shinozaki, 1993). Because the induction of the rd22 gene by ABA can be inhibited by the addition of cycloheximide, an inhibitor of protein biosynthesis, the induction of this gene …… 此处隐藏：49337字，全部文档内容请下载后查看。喜欢就下载吧 ……