Vital role for the J-domain protein Mdj1 in asexual development, multiple stress tolerance, and virulence of Beauveria bassiana.

Mdj1 is a member of the Hsp40 family containing a DnaJ or J domain. Here, we have examined the functions of an Mdj1 orthologue (56.68 kDa) in Beauveria bassiana, a filamentous fungal insect pathogen widely applied in biological control of insect pests. Deletion of mdj1 in B. bassiana resulted in significant growth defects on a variety of complex and minimal media. The Δmdj1 mutant exhibited not only a drastic reduction (92 %) in aerial conidiation during optimal cultivation but also a remarkable decrease (77 %) in submerged blastospore production. Compared to wild-type, the deletion mutant was significantly more sensitive to the stresses of cell wall perturbation, high osmolarity, oxidation, carbendazim fungicide, several metal ions, and acidic/alkaline pH during conidial germination and/or colony growth. In the mutant, conidial thermotolerance and UV-B resistance decreased by 61 and 25 %, respectively, and virulence to Galleria mellonella larvae was largely attenuated. Transcript levels of many phenotype-related genes were drastically suppressed in the absence of mdj1, accompanied with impaired cell walls and reduced intracellular anti-stress molecules, including superoxide dismutases, catalases, glycerol, trehalose, and mannitol. These data indicate that Mdj1 plays a vital role in normal fungal development and contributes significantly to the biological control potential of B. bassiana against insect pests.