Roles of Sti1, a homolog to mammalian Hop, in conidiation, environmental adaptation, and virulence of Beauveria bassiana

Abstract

The stress-induced auxiliary chaperone protein Sti1, a homolog to mammalian Hop, played important but differential roles in environmental adaptation and virulence of various fungi, but the roles of Sti1 in filamentous entomopathogens are not well understood. Here, the roles of Sti1 were unveiled in Beauveria bassiana, a classical entomopathogen widely applied as fungal pesticides to insect control. The disruption of sti1 led to a 68.88 % reduction in colony area at 33 °C and a 28.88 % decrease in median lethal time (LT₅₀) of conidia at 45 °C, but demonstrated a comparable hyphal growth and conidial germination to the control strains (the wild-type strain and complementation mutants) under normal condition. Moreover, the deletion of sti1 caused a reduction in conidiophores and then resulted in a 33.95–43.49 % decrease in conidiation after an incubation of 4–5 days. Additionally, the sti1-deficient mutants displayed impaired cell wall integrity and increased sensitivities to various stressors, including H₂O₂, menadione, NaCl, carbendazim, and UV-B radiation. Furthermore, the Δsti1 showed a 28.07 % delay in virulence to Galleria mellonella larvae via normal infection. These findings were consistent with the reduced production of glycerol, trehalose, mannitol, superoxide dismutases, and catalases. These findings indicate that Sti1 is important for conidiation, environmental adaptation, and pathogenicity of B. bassiana.