Dynamic changes of phosphatidylinositol and phosphatidylinositol 4-phosphate levels modulate H+-ATPase and Na+/H+ antiporter activities to maintain ion homeostasis in Arabidopsis under salt stress.

Abstract Plant metabolites are dynamically modified and distributed under environmental changes. However, it is poorly understood how metabolites change functions in plant stress responses. Maintaining ion homeostasis under salt stress requires coordinately activating two type central regulators: PM H+-ATPase and Na+/H+ antiporter. Here, we used a bioassay-guided isolation approach to identify endogenous small molecules, which affect PM H+-ATPase and Na+/H+ antiporter activities, and found phosphatidylinositol (PI), which inhibits PM H+-ATPase activity in non-stress conditions in Arabidopsis by directly binding to the C-terminus of the PM H+-ATPase AHA2. Under salt stress, the PI4P-to-PI ratio increased, PI4P bound and activated PM Na+/H+ antiporter activity. PI prefers binding to the inactive form of PM H+-ATPase, while PI4P tends to bind the active form of Na+/H+ antiporter. Consistently, pis1 mutants, with reduced levels of PI, displayed increased PM H+-ATPase activity and salt stress tolerance, while pi4kβ1 mutant, with reduced levels of PI4P, displayed reduced PM Na+/H+ antiporter activity and salt stress tolerance. Collectively, we have revealed a dynamic change between PI and PI4P in response to salt stress in Arabidopsis, which is crucial for maintaining ion homeostasis to protect plants from unfavorable environmental conditions.