Participation of Endomembrane Cation/H+ Exchanger AtCHX20 in Osmoregulation of Guard Cells

警卫室 拟南芥 突变体 内膜系统 反转运蛋白 生物 渗透调节 生物化学 拟南芥 反转运蛋白 膨胀压力 细胞生物学 野生型 酿酒酵母 钠氢反转运蛋白 化学 酵母 生物物理学 基因 小泡 盐度 有机化学 生态学
作者
Senthilkumar Padmanaban,Salil Chanroj,June M. Kwak,Xiyan Li,John M. Ward,Heven Sze
出处
期刊:Plant Physiology [Oxford University Press]
卷期号:144 (1): 82-93 被引量:110
标识
DOI:10.1104/pp.106.092155
摘要

Abstract Guard cell movement is induced by environmental and hormonal signals that cause changes in turgor through changes in uptake or release of solutes and water. Several transporters mediating these fluxes at the plasma membrane have been characterized; however, less is known about transport at endomembranes. CHX20, a member of a poorly understood cation/H+ exchanger gene family in Arabidopsis (Arabidopsis thaliana), is preferentially and highly expressed in guard cells as shown by promoter∷β-glucuronidase activity and by whole-genome microarray. Interestingly, three independent homozygous mutants carrying T-DNA insertions in CHX20 showed 35% reduction in light-induced stomatal opening compared to wild-type plants. To test the biochemical function of CHX20, cDNA was expressed in a yeast (Saccharomyces cerevisiae) mutant that lacks Na+(K+)/H+ antiporters (Δnhx1 Δnha1 Δkha1) and plasma membrane Na+ pumps (Δena1-4). Curiously, CHX20 did not enhance tolerance of mutants to moderate Na+ or high K+ stress. Instead, it restored growth of the mutant on medium with low K+ at slightly alkaline pH, but had no effect on growth at acidic pH. Green fluorescent protein-tagged CHX20 expressed in mesophyll protoplasts was localized mainly to membranes of the endosomal system. Furthermore, light-induced stomatal opening of the Arabidopsis mutants was insensitive to external pH and was impaired at high KCl. The results are consistent with the idea that, in exchanging K+ for H+, CHX20 maintains K+ homeostasis and influences pH under certain conditions. Together, these results provide genetic and biochemical evidence that one CHX protein plays a critical role in osmoregulation through K+ fluxes and possibly pH modulation of an active endomembrane system in guard cells.

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