Deciphering the mechanisms underlying cadmium tolerance in the endophytic fungus Trichoderma atroviride D16

Human activities have caused substantial heavy metal contamination, with cadmium (Cd(II)) presenting a notable hazard due to its persistence and tendency to accumulate in living organisms, leading to severe toxicity across various ecological levels. This research investigates the tolerance of the endophytic fungus Trichoderma atroviride D16, derived from Salvia miltiorrhiza, to Cd(II) as a promising and economical approach for Cd(II) mitigation. At exogenous Cd(II) concentrations of ≥150 mg L^-1, the colony growth diameter of D16 showed little change, with a tolerance index consistently maintained between 0.82 and 0.93 on the fifth day of cultivation. The Cd(II) tolerance EC₅₀ (half-maximal effective concentration) concentration of D16 was determined to be 47.21 mg L^-1 in liquid culture. Concurrently, the strain's Cd(II) adsorption efficiency was between 20.9% and 37.6%. Under elevated Cd(II) concentrations, D16 exhibited significant upregulation of superoxide dismutase (SOD), glutathione peroxidase (GPX) and glutathione (GSH) actively contributing to Cd(II) detoxification. Transcriptome analysis identified three primary response pathways to Cd(II) stress: transmembrane transporter, chelation, and regulation of antioxidant enzyme activity. Genes related to cadmium transporter, glutathione synthesis, and antioxidant enzymes were notably upregulated at 50 mg L^-1 Cd(II), indicating that gene expression regulation is crucial for D16's high Cd(II) tolerance. In Arabidopsis thaliana exposed to 50 mg kg^-1 Cd(II), D16 inoculation significantly enhanced biomass and reduced Cd(II) accumulation. Mechanistically, D16 mitigated stress by enhancing host antioxidant activity and regulating key Cd-responsive genes to restrict Cd uptake and promote detoxification. In conclusion, D16 possesses robust self-resistance and actively fortifies host plant tolerance, offering essential microbial resources and theoretical support for the bioremediation of Cd(II) contamination.