Role of the Global Fitness Regulator Genes on the Osmotic Tolerance Ability and Salinity Hazard Alleviation of Trichoderma asperellum GDFS 1009 for Sustainable Agriculture

Velvet family proteins are global regulators of fungal growth and development. Here, we reported the role of Vel1 and Lae1 from T. asperellum in osmotic tolerance. Deletion of the Vel1 and Lae1 genes led to the retardation of vegetative mycelial growth under saline conditions. The strain carrying the overexpression locus of the Vel1 and Lae1 genes was highly resistant to oxidative stress by upregulating the enzymes and genes involved in antioxidant activity. Major physiological changes in the cell wall and vacuoles occurred under high saline conditions. The Vel1 and Lae1 overexpression strains increased cell wall thickness and the number of vacuoles, which seems to lead to an increase of the osmolyte content of glycerol and proline. The absorption of Na(+) content in the vacuole of the Vel1 and Lae1 overexpression strains was increased, while the absorption of Na(+) was impaired in the Vel1 and Lae1 knock out strains, in which the Na(+) was localized in the cell wall membrane. This result supported the significant correlation of the expression of genes with the ionic transportation in T. asperellum. Maize root colonization by the Vel1 and Lae1 gene overexpression strain was increased, which would mitigate the stress caused by the absorption of Na(+) in the maize roots and increased the plant growth. Our results highlighted the importance of Vel1 and Lae1 proteins to the salinity stress tolerance of T. asperellum and the mitigation of Na(+) stress to plants for sustainable agriculture.