Comparative physiological and transcriptomic analyses of zoysiagrass (<i>Zoysia japonica</i>) species reveal key metabolic pathways for salt tolerance

Soil salinity is a significant environmental challenge that adversely affects plant yield and quality. Zoysiagrass (<italic>Zoysia japonica</italic>), a member of the Gramineae family, is highly salt-tolerant, making it an excellent model for studying salt stress response mechanisms. We performed physiological and transcriptomic analyses on two contrasting Zoysiagrass germplasm accessions under high salt conditions. The salt-tolerant germplasm ST68 demonstrated superior growth phenotypes, higher chlorophyll and relative water content, greater photochemical efficiency, and lower relative electrolyte leakage and sodium ion content compared to the salt-sensitive germplasm SS9. Transcriptomic analysis revealed differential expression in pathways involved in photosynthesis, flavonoid biosynthesis, cell wall macromolecule catabolism, phosphate ion homeostasis, and reactive oxygen species response in the tolerant vs the sensitive line under salt stress. Notably, the <italic>ZjHEMA</italic> gene, which encodes glutamyl-tRNA reductase, a rate-limiting enzyme in chlorophyll biosynthesis, was identified as a key regulator due to its significant upregulation under salt stress in the salt-tolerant germplasm, compared to the sensitive one. Overexpression of the salt-responsive glutamyl-tRNA reductase gene, associated with chlorophyll metabolism in Zoysiagrass, in Arabidopsis led to increased salt tolerance, as evidenced by elevated chlorophyll content, relative water content, and photochemical efficiency compared to wild-type plants. Our findings offer new insights into the mechanisms of salt tolerance in Zoysiagrass, laying a foundation for breeding salt-tolerant germplasm.