Department of Biochemistry, Center for Molecular Protein Science, Lund University, PO Box 124, SE-221 00, Lund, Sweden.
Plant J. 2010 Feb;61(4):650-60. doi: 10.1111/j.1365-313X.2009.04087.x. Epub 2009 Nov 26.
Aquaporins facilitate water transport over cellular membranes, and are therefore believed to play an important role in water homeostasis. In higher plants aquaporin-like proteins, also called major intrinsic proteins (MIPs), are divided into five subfamilies. We have previously shown that MIP transcription in Arabidopsis thaliana is generally downregulated in leaves upon drought stress, apart from two members of the plasma membrane intrinsic protein (PIP) subfamily, AtPIP1;4 and AtPIP2;5, which are upregulated. In order to assess whether this regulation is general or accession-specific we monitored the gene expression of all PIPs in five Arabidopsis accessions. The overall drought regulation of PIPs was well conserved for all five accessions tested, suggesting a general and fundamental physiological role of this drought response. In addition, significant differences among accessions were identified for transcripts of three PIP genes. Principal component analysis showed that most of the PIP transcriptional variation during drought stress could be explained by one variable linked to leaf water content. Promoter-GUS constructs of AtPIP1;4, AtPIP2;5 and also AtPIP2;6, which is unresponsive to drought stress, had distinct expression patterns concentrated in the base of the leaf petioles and parts of the flowers. The presence of drought stress response elements within the 1.6-kb promoter regions of AtPIP1;4 and AtPIP2;5 was demonstrated by comparing transcription of the promoter reporter construct and the endogenous gene upon drought stress. Analysis by ATTED-II and other web-based bioinformatical tools showed that several of the MIPs downregulated upon drought are strongly co-expressed, whereas AtPIP1;4, AtPIP2;5 and AtPIP2;6 are not co-expressed.
水通道蛋白促进水在细胞膜上的运输，因此被认为在水稳态中发挥重要作用。在高等植物中，水通道蛋白样蛋白，也称为主要内在蛋白 (MIPs)，分为五个亚家族。我们之前已经表明，拟南芥的 MIP 转录通常在干旱胁迫下叶片下调，除了质膜内在蛋白 (PIP) 亚家族的两个成员 AtPIP1;4 和 AtPIP2;5 上调。为了评估这种调节是普遍的还是特定于入口的，我们监测了五个拟南芥入口中所有 PIP 的基因表达。所有五个入口测试的 PIP 的总体干旱调节都得到了很好的保守，表明这种干旱反应具有普遍和基本的生理作用。此外，还确定了三个 PIP 基因的转录本之间存在显著差异。主成分分析表明，在干旱胁迫期间，大多数 PIP 转录变化可以用一个与叶片含水量相关的变量来解释。AtPIP1;4、AtPIP2;5 和对干旱胁迫无反应的 AtPIP2;6 的启动子-GUS 构建体具有集中在叶片叶柄基部和部分花朵的不同表达模式。通过比较干旱胁迫下启动子报告构建体和内源性基因的转录，证明了 AtPIP1;4 和 AtPIP2;5 的 1.6-kb 启动子区域内存在干旱应激反应元件。通过 ATTED-II 和其他基于网络的生物信息学工具进行的分析表明，在干旱胁迫下下调的多个 MIPs 强烈共表达，而 AtPIP1;4、AtPIP2;5 和 AtPIP2;6 则不共表达。
