Hugouvieux Véronique, Murata Yoshiyuki, Young Jared J, Kwak June M, Mackesy Daniel Z, Schroeder Julian I
Division of Biology, Cell, and Developmental Biology Section, and Center for Molecular Genetics, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093-0116, USA.
Plant Physiol. 2002 Nov;130(3):1276-87. doi: 10.1104/pp.009480.
Abscisic acid (ABA) regulates developmental processes and abiotic stress responses in plants. We recently characterized a new Arabidopsis mutant, abh1, which shows ABA-hypersensitive regulation of seed germination, stomatal closing, and cytosolic calcium increases in guard cells (V. Hugouvieux, J.M. Kwak, J.I. Schroeder [2001] Cell 106: 477-487). ABH1 encodes the large subunit of a dimeric Arabidopsis mRNA cap-binding complex and in expression profiling experiments was shown to affect mRNA levels of a subset of genes. Here, we show that the dimeric ABH1 and AtCBP20 subunits are ubiquitously expressed. Whole-plant growth phenotypes of abh1 are described and properties of ABH1 in guard cells are further analyzed. Complemented abh1 lines expressing a green fluorescent protein-ABH1 fusion protein demonstrate that ABH1 mainly localizes in guard cell nuclei. Stomatal apertures were smaller in abh1 compared with wild type (WT) when plants were grown at 40% humidity, and similar at 95% humidity. Correlated with stomatal apertures from plants grown at 40% humidity, slow anion channel currents were enhanced and inward potassium channel currents were decreased in abh1 guard cells compared with WT. Gas exchange measurements showed similar primary humidity responses in abh1 and WT, which together with results from abh1/abi1-1 double-mutant analyses suggest that abh1 shows enhanced sensitivity to endogenous ABA. Double-mutant analyses of the ABA-hypersensitive signaling mutants, era1-2 and abh1, showed complex genetic interactions, suggesting that ABH1 and ERA1 do not modulate the same negative regulator in ABA signaling. Mutations in the RNA-binding protein sad1 showed hypersensitive ABA-induced stomatal closing, whereas hyl1 did not affect this response. These data provide evidence for the model that the mRNA-processing proteins ABH1 and SAD1 function as negative regulators in guard cell ABA signaling.
脱落酸（ABA）调控植物的发育过程及非生物胁迫响应。我们最近鉴定了一种新的拟南芥突变体abh1，该突变体在种子萌发、气孔关闭以及保卫细胞胞质钙增加方面表现出对ABA的超敏调控（V. Hugouvieux，J.M. Kwak，J.I. Schroeder [2001] Cell 106: 477 - 487）。ABH1编码一种二聚体拟南芥mRNA帽结合复合物的大亚基，并且在表达谱实验中显示会影响一部分基因的mRNA水平。在此，我们表明二聚体ABH1和AtCBP20亚基在植物中普遍表达。描述了abh1的整株植物生长表型，并进一步分析了ABH1在保卫细胞中的特性。表达绿色荧光蛋白 - ABH1融合蛋白的互补abh1株系表明ABH1主要定位于保卫细胞核。当植物在40%湿度下生长时，abh1的气孔孔径比野生型（WT）小，而在95%湿度下两者相似。与在40%湿度下生长的植物的气孔孔径相关，与WT相比，abh1保卫细胞中的慢阴离子通道电流增强，内向钾通道电流减小。气体交换测量表明abh1和WT对湿度的主要响应相似，这与abh1/abi1 - 1双突变体分析结果一起表明abh1对内源ABA表现出增强的敏感性。ABA超敏信号突变体era1 - 2和abh1的双突变体分析显示出复杂的遗传相互作用，表明ABH1和ERA1在ABA信号传导中不调控同一个负调节因子。RNA结合蛋白sad1的突变表现出对ABA诱导的气孔关闭超敏，而hyl1不影响这种响应。这些数据为mRNA加工蛋白ABH1和SAD1在保卫细胞ABA信号传导中作为负调节因子的模型提供了证据。
