Tissue-specific accumulation of pH-sensing phosphatidic acid determines plant stress tolerance.

The signalling lipid phosphatidic acid (PA) is involved in regulating various fundamental biological processes in plants. However, the mechanisms of PA action remain poorly understood because currently available methods for monitoring PA fail to determine the precise spatio-temporal dynamics of this messenger in living cells and tissues of plants. Here, we have developed PAleon, a PA-specific optogenetic biosensor that reports the concentration and dynamics of bioactive PA at the plasma membrane based on Förster resonance energy transfer (FRET). PAleon was sensitive enough to monitor physiological concentrations of PA in living cells and to visualize PA dynamics at subcellular resolution in tissues when they were challenged with abscisic acid (ABA) and salt stress. PAleon bioimaging revealed kinetics and tissue specificity of salt stress-triggered PA accumulation. Compared with wild-type Arabidopsis, the pldα1 mutant lacking phospholipase Dα1 (PLDα1) for PA generation showed delayed and reduced PA accumulation. Comparative analysis of wild type and pldα1 mutant indicated that cellular pH-modulated PA interaction with target proteins and PLD/PA-mediated salt tolerance. Application of the PA biosensor PAleon uncovered specific spatio-temporal PA dynamics in plant tissues. Our findings suggest that PA signalling integrates with cellular pH dynamics to mediate plant response to salt stress.