Regulative roles of glutathione reductase and four glutaredoxins in glutathione redox, antioxidant activity, and iron homeostasis of Beauveria bassiana

Multiple glutaredoxins (Grx) and glutathione reductase (Glr) are vital for the thiol-disulfide redox system in budding yeast but generally unexplored in filamentous fungi. Here we characterized the Beauveria bassiana redox system comprising dithiol Grx1, monothiol Grx2–4, Grx-like Grx5, and Glr orthologue. Each grx or glr deletion was compensated by increased transcripts of some other grx genes in normal cultures. Particularly, grx3 compensated the absence of grx1 , grx2 , grx5 , or glr under oxidative stress while its absence was compensated only by undeletable grx4 under normal conditions but by most of other undeleted grx and glr genes in response to menadione. Consequently, the redox state was disturbed in Δ glr more than in Δ grx3 but not in Δ grx1 / 2 / 5 . Superoxide dismutases were more active in normal Δ grx1 – 3 cultures but less in Δ grx5 or Δ glr response to menadione. Total catalase activity increased differentially in all the mutant cultures stressed with or without H 2 O 2 while total peroxidase activity decreased more in the normal or H 2 O 2 -stressed culture of Δ glr than of Δ grx3 . Among the mutants, Δ grx3 showed slightly increased sensitivity to menadione or H 2 O 2 ; Δ glr exhibited greater sensitivity to thiol-oxidizing diamide than thiol-reducing 1-chloro-2,4-dinitrobenzene as well as increased sensitivity to the two oxidants. Intriguingly, all the mutants grew slower in a Fe 3+ -inclusive medium perhaps due to elevated transcripts of two Fe 3+ transporter genes. More or fewer phenotypes linked with biocontrol potential were altered in four deletion mutants excluding Δ grx5 . All the changes were restored by targeted gene complementation. Overall, Grx3 played more critical role than other Grx homologues in the Glr-dependent redox system of the fungal entomopathogen.