Catalases play differentiated roles in the adaptation of a fungal entomopathogen to environmental stresses


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Abstract

SummaryThe catalase family ofBeauveria bassiana(fungal entomopathogen) consists of catA (spore-specific), catB (secreted), catP (peroxisomal), catC (cytoplasmic) and catD (secreted peroxidase/catalase), which were distinguished in phylogeny and structure and functionally characterized by constructing single-gene disrupted and rescued mutants for enzymatic and multi-phenotypic analyses. Total catalase activity decreased 89% and 56% in ΔcatBand ΔcatP, corresponding to the losses of upper and lower active bands gel-profiled for all catalases respectively, but only 9−12% in other knockout mutants. Compared with wild type and complement mutants sharing similar enzymatic and phenotypic parameters, all knockout mutants showed significant (9−56%) decreases in the antioxidant capability of their conidia (active ingredients of mycoinsecticides), followed by remarkable phenotypic defects associated with the fungal biocontrol potential. These defects included mainly the losses of 40% thermotolerance (45°C) in ΔcatA, 46−48% UV-B resistance in ΔcatAand ΔcatD, and 33−47% virulence toSpodoptera lituralarvae in ΔcatA, ΔcatPand ΔcatDrespectively. Moreover, the drastic transcript upregulation of some other catalase genes observed in the normal culture of each knockout mutant revealed functionally complimentary effects among some of the catalase genes, particularly betweencatBandcatCwhose knockout mutants displayed little or minor phenotypic changes. However, the five catalase genes functioned redundantly in mediating the fungal tolerance to either hyperosmotic or fungicidal stress. The differentiated roles of five catalases in regulating theB. bassianavirulence and tolerances to oxidative stress, high temperature and UV-B irradiation provide new insights into fungal adaptation to stressful environment and host invasion.

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