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

Abstract

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 Δglr more than in Δgrx3 but not in Δgrx1/2/5. Superoxide dismutases were more active in normal Δgrx1–3 cultures but less in Δgrx5 or Δglr response to menadione. Total catalase activity increased differentially in all the mutant cultures stressed with or without H₂O₂ while total peroxidase activity decreased more in the normal or H₂O₂-stressed culture of Δglr than of Δgrx3. Among the mutants, Δgrx3 showed slightly increased sensitivity to menadione or H₂O₂; Δglr 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 Fe³⁺-inclusive medium perhaps due to elevated transcripts of two Fe³⁺ transporter genes. More or fewer phenotypes linked with biocontrol potential were altered in four deletion mutants excluding Δgrx5. 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.