Molecular analysis of plant gene expression by phytohormone abscisic acid.

环境胁迫，如干旱、低温和盐胁迫，会触发植物激素脱落酸(ABA)的产生，进而诱导各种基因的表达。ABA在气孔关闭、种子成熟和休眠中起作用。许多ABA诱导基因也在种子发育的胚胎发育后期表达。为了了解水分胁迫信号转导到基因表达的分子过程，我们通过差异筛选的方法克隆了25个水分胁迫诱导基因的cDNAs(命名为RD或ERD)。由这些RD启动子驱动的GUS报告基因在转基因植株中受到脱水和ABA的显著诱导。我们对rd29A启动子进行了精确的分析，发现了一个新的含有9个碱基的顺式作用元件，TACCGACAT(DRE，脱水反应元件)，它参与了脱水应答表达。ABRE(YACGTGGC)是ABA反应元件之一。凝胶滞留分析检测到与顺式作用元件结合的核蛋白(S)。RD22的诱导由脱落酸介导，但其依赖于脱落酸的表达需要蛋白质的生物合成。Rd22启动子的一个67bp的区域是其ABA应答表达所必需的，它包含几个保守的DNA结合蛋白基序，如MYC和MYB，但不包含Abres。最近，以67个碱基的DNA为探针，用Southwest方法克隆了一个转录因子MYC同源物的cDNA，这表明干旱诱导的MYC同源物可能在ABA诱导的rd22表达中发挥作用。这些结果表明，干旱或脱落酸诱导转录因子(S)在干旱胁迫下脱落酸应答基因的表达中发挥作用，并且存在两个独立的转录系统，一个是abre/bZIP系统，另一个可能需要脱落酸诱导转录因子(S)的从头合成。

Environmental stresses, such as drought, low temperature and salt stresses, trigger the production of plant hormone abscisic acid (ABA), which in turn induces various genes. ABA functions in stomata closure, seed maturation and dormancy. Many ABA inducible genes are also expressed at the late stage of embryogenesis during seed development.To understand the molecular process of signal transduction from initial water-stress signal to gene expression, we cloned 25 cDNAs (named RD or ERD) for genes that are induced by water stress by differential screening. The GUS reporter gene driven by these rd promoters was induced at significant level by dehydration and ABA in transgenic plants. We precisely analyzed the rd29A promoter and identified a novel cis-acting element containing 9 bp, TACCGACAT (DRE,Dehydration Responsive Element), that is involved in dehydration-responsive expression. ABRE (YACGTGGC) functions as one of the ABA responsive elements. Nuclear protein(s) that bind to the cis-acting element was detected with gel retardation assay.The induction of 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 no ABREs. Recently, 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) function in the ABA-responsive gene expression under drought stress, and that there are two independent transcription system for ABA-responsive gene expression, one is ABRE/bZIP system and the other may require de novo synthesis of ABA-inducible transcription factor(s).