The DUF1996 and WSC domain-containing protein Wsc1I acts as a novel sensor of multiple stress cues in Beauveria bassiana.

Wsc1I homologues featuring both an N-terminal DUF1996 (domain of unknown function 1996) and a C-terminal WSC (cell wall stress-responsive component) domain exist in filamentous fungi but have never been functionally characterized. Here, Wsc1I is shown to localize in the vacuoles and cell wall/membrane of the insect mycopathogen Beauveria bassiana and hence linked to cell membrane- and vacuole-related cellular events. In B. bassiana, deletion of Wsc1I resulted in marked increases of hyphal and conidial sensitivities to hyperosmotic agents, oxidants, cell wall perturbing chemicals, and metal cations (Cu2+ , Zn2+ , Fe2+ , and Mg2+ ) despite slight impact on normal growth and conidiation. Conidia produced by the deletion mutant showed not only reduced tolerance to both 45°C heat and UVB irradiation but also attenuated virulence to a susceptible insect through normal cuticle infection or cuticle-bypassing infection. Importantly, phosphorylation of the mitogen-activated protein kinase Hog1 was largely attenuated or nearly abolished in the Wsc1I-free cells triggered with hyperosmotic, oxidative, or cell wall perturbing stress. All changes were well restored by targeted gene complementation. Our findings highlight a novel role of Wsc1I in sensing multiple stress cues upstream of the Hog1 signalling pathway and its pleiotropic effects in B. bassiana.