Transcriptomic Profiling Reveals Key Gene in Trichoderma guizhouense NJAU4742 Enhancing Tomato Tolerance Under Saline Conditions

Soil salinity stress inhibits the growth of most beneficial soil fungi, thereby adversely affecting crop growth, though the underlying mechanisms remain poorly understood. Our study revealed that the beneficial fungus Trichoderma guizhouense NJAU4742 exhibited limited salt tolerance, with its growth being significantly suppressed under elevated salinity. To investigate the physiological, biochemical, and molecular responses of NJAU4742 to salt stress and its subsequent effects on tomato growth, we subjected NJAU4742 to X-ray irradiation, aiming to obtain mutants with altered salt tolerance. A forward mutant strain (designated M15) displaying near-complete loss of salt tolerance was successfully isolated. Comparative transcriptomic analysis between the wild type (wt) and M15 identified gene Tgmfs, a salt stress-responsive gene belonging to the major facilitator superfamily. By constructing Tgmfs knockout (Tgmfs-KO) and overexpression (Tgmfs-OE) strains, we observed that Tgmfs deletion caused intracellular Na+ accumulation in NJAU4742, prompting compensatory upregulation of Na+/K+-ATPase activity to maintain ion homeostasis. Concurrently, salt stress induced reactive oxygen species accumulation and oxidative stress in fungal cells, which was counteracted by enhanced superoxide dismutase activity and an elevated NAD+/NADH ratio, collectively boosting antioxidant defenses. Pot experiments demonstrated that the application of Tgmfs-OE or wt spore suspensions markedly improved tomato salt tolerance, with Tgmfs-OE treatment showing superior efficacy. This study advances our understanding of filamentous fungal salt adaptation mechanisms and their synergistic effects on plant resilience.