Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
J Plant Res. 2011 Jul;124(4):527-38. doi: 10.1007/s10265-011-0426-x. Epub 2011 May 12.
Mg-chelatase H subunit (CHLH) is a multifunctional protein involved in chlorophyll synthesis, plastid-to-nucleus retrograde signaling, and ABA perception. However, whether CHLH acts as an actual ABA receptor remains controversial. Here we present evidence that CHLH affects ABA signaling in stomatal guard cells but is not itself an ABA receptor. We screened ethyl methanesulfonate-treated Arabidopsis thaliana plants with a focus on stomatal aperture-dependent water loss in detached leaves and isolated a rapid transpiration in detached leaves 1 (rtl1) mutant that we identified as a novel missense mutant of CHLH. The rtl1 and CHLH RNAi plants showed phenotypes in which stomatal movements were insensitive to ABA, while the rtl1 phenotype showed normal sensitivity to ABA with respect to seed germination and root growth. ABA-binding analyses using (3)H-labeled ABA revealed that recombinant CHLH did not bind ABA, but recombinant pyrabactin resistance 1, a reliable ABA receptor used as a control, showed specific binding. Moreover, we found that the rtl1 mutant showed ABA-induced stomatal closure when a high concentration of extracellular Ca(2+) was present and that a knockout mutant of Mg-chelatase I subunit (chli1) showed the same ABA-insensitive phenotype as rtl1. These results suggest that the Mg-chelatase complex as a whole affects the ABA-signaling pathway for stomatal movements.
镁螯合酶 H 亚基（CHLH）是一种多功能蛋白，参与叶绿素合成、质体到核的逆行信号转导以及 ABA 感知。然而，CHLH 是否作为实际的 ABA 受体仍然存在争议。在这里，我们提供的证据表明，CHLH 影响保卫细胞中的 ABA 信号转导，但它本身不是 ABA 受体。我们筛选了经乙基磺酸甲酯处理的拟南芥植物，重点关注离体叶片中气孔开度依赖性水分损失，并分离出一个快速蒸腾的离体叶片 1（rtl1）突变体，我们将其鉴定为 CHLH 的一种新型错义突变体。rtl1 和 CHLH RNAi 植物表现出气孔运动对 ABA 不敏感的表型，而 rtl1 表型对种子萌发和根生长的 ABA 表现出正常的敏感性。使用（3）H 标记的 ABA 进行的 ABA 结合分析表明，重组 CHLH 不结合 ABA，但作为对照的重组 pyrabactin 抗性 1（一种可靠的 ABA 受体）显示出特异性结合。此外，我们发现 rtl1 突变体在存在高浓度细胞外 Ca(2+)时表现出 ABA 诱导的气孔关闭，而 Mg-螯合酶 I 亚基（chli1）的敲除突变体表现出与 rtl1 相同的 ABA 不敏感表型。这些结果表明，整个镁螯合酶复合物影响气孔运动的 ABA 信号通路。
