The hex1 gene of Trichoderma simmonsii is involved in stress responses, biocontrol potential and wheat plant growth

Woronin bodies are unique organelles in Pezizomycotina fungi that allow hyphae compartmentalization and prevent cytoplasmatic bleeding after mechanical injury. Several studies have related the peroxisomal protein HEX1, the major component of Woronin bodies with other biological processes such as hyphal growth, osmotic stress tolerance and pathogenicity. Trichoderma spp. are plant-beneficial multipurpose biological control agents, and proteomic and transcriptomic studies have shown that HEX1 and its corresponding gene are overrepresented when grown in the presence of fungal cell walls and plant polymers. To further investigate the involvement of hex1 in Trichoderma biology, we generated hex1 deletion transformants using the wheat endophytic strain T. simmonsii T137 as host. Results confirmed that hex1 gene is involved in the prevention of cytoplasmatic bleeding, and also has a role in fungal growth and biocontrol potential against phytopathogenic fungi and oomycetes. The involvement of hex1 in the fungal response to osmotic and oxidative stresses is conditioned by the type of stress and by the nutrient richness of the culture medium. The hex1 deletion also affected the interaction with wheat, but did not affect the plant protective effect of T137 against water stress. Overall, this study shows the implication of HEX1 in a wide range of biological processes necessary for T. simmonsii to deploy its abilities to be used as an agriculturally beneficial fungus.