Department of Molecular Biotechnology and Kumho Life Science Laboratory, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 500-757, South Korea.
BMC Plant Biol. 2010 Dec 16;10:277. doi: 10.1186/1471-2229-10-277.
Abscisic acid (ABA) is a plant hormone that controls seed germination, protective responses to various abiotic stresses and seed maturation. The ABA-dependent processes entail changes in gene expression. Numerous genes are regulated by ABA, and promoter analyses of the genes revealed that cis-elements sharing the ACGTGGC consensus sequence are ubiquitous among ABA-regulated gene promoters. The importance of the core sequence, which is generally known as ABA response element (ABRE), has been demonstrated by various experiments, and its cognate transcription factors known as ABFs/AREBs have been identified. Although necessary, ABRE alone is not sufficient, and another cis-element known as "coupling element (CE)" is required for full range ABA-regulation of gene expression. Several CEs are known. However, despite their importance, the cognate transcription factors mediating ABA response via CEs have not been reported to date. Here, we report the isolation of transcription factors that bind one of the coupling elements, CE1.
To isolate CE1 binding proteins, we carried out yeast one-hybrid screens. Reporter genes containing a trimer of the CE1 element were prepared and introduced into a yeast strain. The yeast was transformed with library DNA that represents RNA isolated from ABA-treated Arabidopsis seedlings. From the screen of 3.6 million yeast transformants, we isolated 78 positive clones. Analysis of the clones revealed that a group of AP2/ERF domain proteins binds the CE1 element. We investigated their expression patterns and analyzed their overexpression lines to investigate the in vivo functions of the CE element binding factors (CEBFs). Here, we show that one of the CEBFs, AtERF13, confers ABA hypersensitivity in Arabidopsis, whereas two other CEBFs enhance sugar sensitivity.
Our results indicate that a group of AP2/ERF superfamily proteins interacts with CE1. Several CEBFs are known to mediate defense or abiotic stress response, but the physiological functions of other CEBFs remain to be determined. Our in vivo functional analysis of several CEBFs suggests that they are likely to be involved in ABA and/or sugar response. Together with previous results reported by others, our current data raise an interesting possibility that the coupling element CE1 may function not only as an ABRE but also as an element mediating biotic and abiotic stress responses.
脱落酸（ABA）是一种植物激素，控制种子萌发、对各种非生物胁迫的保护反应和种子成熟。ABA 依赖的过程需要基因表达的变化。许多基因受 ABA 调控，对这些基因启动子的分析表明，共享 ACGTGGC 一致序列的顺式元件普遍存在于 ABA 调控的基因启动子中。核心序列（通常称为 ABA 反应元件（ABRE））的重要性已通过各种实验证明，其同源转录因子称为 ABFs/AREBs 已被鉴定。虽然是必要的，但 ABRE 本身并不足以充分发挥作用，还需要另一个顺式元件，称为“偶联元件（CE）”，才能实现基因表达的全范围 ABA 调控。目前已经知道了几个 CE。然而，尽管它们很重要，但介导通过 CE 进行 ABA 反应的同源转录因子尚未被报道。在这里，我们报告了分离与一个偶联元件 CE1 结合的转录因子的情况。
为了分离 CE1 结合蛋白，我们进行了酵母单杂交筛选。制备了含有 CE1 元件三聚体的报告基因，并将其导入酵母菌株。用代表 ABA 处理的拟南芥幼苗中分离的 RNA 的文库 DNA 转化酵母。从 360 万个酵母转化体的筛选中，我们分离出了 78 个阳性克隆。对克隆的分析表明，一组 AP2/ERF 结构域蛋白结合 CE1 元件。我们研究了它们的表达模式，并分析了它们的过表达系，以研究 CE 元件结合因子（CEBFs）的体内功能。在这里，我们表明 CEBF 中的一个，AtERF13，使拟南芥对 ABA 敏感，而另外两个 CEBF 增强了对糖的敏感性。
我们的结果表明，一组 AP2/ERF 超家族蛋白与 CE1 相互作用。已知几个 CEBF 介导防御或非生物胁迫反应，但其他 CEBF 的生理功能仍有待确定。我们对几个 CEBF 的体内功能分析表明，它们可能参与 ABA 和/或糖反应。结合其他人之前报告的结果，我们目前的数据提出了一个有趣的可能性，即偶联元件 CE1 不仅可以作为 ABRE，还可以作为介导生物和非生物胁迫反应的元件。
