Abstract
Plants possess remarkable ability to adapt to adverse environmental conditions. The adaptation process involves the removal of many molecules from organelles, especially membranes, and replacing them with new ones. The process is mediated by an intracellular vesicle-trafficking system regulated by phosphatidylinositol (PtdIns) kinases and phosphatases. Although PtdIns comprise a fraction of membrane lipids, they function as major regulators of stress signaling. We analyzed the role of PtdIns 5-phosphatases (5PTases) in plant salt tolerance. The Arabidopsis (Arabidopsis thaliana) genome contains 15 At5PTases. We analyzed salt sensitivity in nine At5ptase mutants and identified one (At5ptase7) that showed increased sensitivity, which was improved by overexpression. At5ptase7 mutants demonstrated reduced production of reactive oxygen species (ROS). Supplementation of mutants with exogenous PtdIns dephosphorylated at the D5' position restored ROS production, while PtdIns(4,5)P(2), PtdIns(3,5)P(2), or PtdIns(3,4,5)P(3) were ineffective. Compromised salt tolerance was also observed in mutant NADPH Oxidase, in agreement with the low ROS production and salt sensitivity of PtdIns 3-kinase mutants and with the inhibition of NADPH oxidase activity in wild-type plants. Localization of green fluorescent protein-labeled At5PTase7 occurred in the plasma membrane and nucleus, places that coincided with ROS production. Analysis of salt-responsive gene expression showed that mutants failed to induce the RD29A and RD22 genes, which contain several ROS-dependent elements in their promoters. Inhibition of ROS production by diphenylene iodonium suppressed gene induction. In summary, our results show a nonredundant function of At5PTase7 in salt stress response by regulating ROS production and gene expression.
Highlights
Plants possess remarkable ability to adapt to adverse environmental conditions
We have shown previously that reactive oxygen species (ROS) production during salt stress is caused by NADPH oxidase (Mazel et al, 2004)
We show a specific function of At5PTase7 in plant salt tolerance: gene knockout reduced the production of ROS, resulting in reduced salt tolerance (Figs. 1 and 3)
Summary
Plants possess remarkable ability to adapt to adverse environmental conditions. The adaptation process involves the removal of many molecules from organelles, especially membranes, and replacing them with new ones. We analyzed the role of PtdIns 5-phosphatases (5PTases) in plant salt tolerance. Our results show a nonredundant function of At5PTase in salt stress response by regulating ROS production and gene expression. The PtdIns 5-phosphatases (5PTases) were shown to be involved in the regulation of plant stress responses (Ercetin and Gillaspy, 2004; Williams et al, 2005). Not all of the components involved in the activation of NADPH oxidase have been identified, several factors that function in animals, such as cytosolic calcium, phosphatidic acid, and ras-related C3 small GTP binding protein were shown to have crucial roles in reactive oxygen species (ROS) production in plants (Potikha et al, 1999; Wong et al, 2007; Monshausen et al, 2009; Zhang et al, 2009). Several Arabidopsis proteins with domain structure similar to mammalian p67phox have been described (van Leeuwen et al, 2004; Sumimoto et al, 2007)
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