Phosphatidic Acid Homeostasis and Membrane Lipid Remodeling Confer Salt Tolerance in Zoysia japonica by Stabilizing Metabolic Networks and a Putative SOS Signaling Activation

Soil salinization poses a major threat to plant growth and ecosystem sustainability. <i>Zoysia japonica</i>, a salt-tolerant turfgrass, shows promise for saline-alkali soil remediation, yet its metabolic adaptation mechanisms remain poorly understood. Here, we applied non-targeted liquid chromatography/mass spectrometry (LC/MS) metabolomics to compare the responses of salt-tolerant (accession 68) and salt-sensitive (accession 9) genotypes of <i>Z. japonica</i> under salt stress. The sensitive genotype exhibited stronger metabolic disruption, with 843 differentially accumulated metabolites (largely down-regulated), compared with 595 in the tolerant genotype (predominantly up-regulated). We identified a coordinated tolerance mechanism primarily centered on lipid remodeling and energy maintenance. The tolerant genotype enhanced membrane stability through the accumulation of saturated glycerophospholipids and an increased phosphatidylcholine/phosphatidylethanolamine (PC/PE) ratio, while maintaining phosphatidic acid (PA) homeostasis which may facilitate SOS-dependent Na⁺ efflux. It also mitigated oxidative damage by stabilizing diacylglycerol (DAG), thereby potentially limiting protein kinase C (PKC) overactivation. Furthermore, sustained cardiolipin and riboflavin metabolism supported mitochondrial energy production in the tolerant genotype. Together, these findings provide new insights into the early metabolic basis of salt tolerance in <i>Z. japonica</i>, suggesting a potential crucial role for PA-mediated regulation of SOS-dependent sodium sequestration during the initial phase of stress, and implying potential targets for breeding stress-resilient turfgrasses.