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. Zoysia japonica, 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 Z. japonica 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 Z. japonica, 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.