Antioxidant activities of four superoxide dismutases in Metarhizium robertsii and their contributions to pest control potential

Abstract

The superoxide dismutase (SOD) family of Metarhizium robertsii, a fungal insect pathogen, comprises six members functionally unknown yet, including Cu/ZnSODs (Sod1/5/6), MnSODs (Sod2/3), and FeSOD (Sod4). Here, we show a mitochondrial localization of Sod3 and Sod4 and a requirement of either sod4 or sod6 for the fungal life as suggested by an inability to be deleted. We found remarked roles of Sod1, Sod2, and Sod3 in sustaining antioxidant activity and the fungal potential against insect pests but no role of Sod5 in all examined phenotypes. Intracellular SOD activity decreased by 49% in Δsod1 and 22% in either Δsod2 or Δsod3. The decreased SOD activities concurred with altered enzymographs, in which one of two SOD-active bands in wild-type and rescued strains disappeared in Δsod1 rather than in Δsod2 and another band disappeared in Δsod3. Consequently, maximal cell sensitivity to superoxide anions generated by oxidant menadione occurred in Δsod1, followed sequentially by Δsod3 and Δsod2. The latter two mutants were more sensitive than Δsod1 to oxidant HO. Transcriptional analysis revealed partial compensation of one or two partner genes upregulated for the absence of sod1, sod2, or sod3 and full compensation of three partners largely upregulated for the absence of sod5, as well as differential expression of most catalase genes in each Δsod mutant. The three mutants also suffered defects in conidial thermotolerance, UVB resistance, and virulence. These findings unveil that, to adapt to different host spectra and habitats, some major SODs in M. roberstii are functionally differentiated from those known previously in Beauveria bassiana, a classic insect mycopathogen lacking Sod6.

Molecular basis and regulatory mechanisms underlying fungal insecticides' resistance to solar ultraviolet irradiation

“…Knockout mutants of four superoxide dismutase (SOD) genes ( sod1‐3 and sod5 ) required for removal of superoxide anions showed larger LD 50 reductions (38–48%) than the knockdown mutants of sod4 (33%), a mitochondrial FeSOD gene essential for the fungal viability 82, 83 . Interestingly, sod1 , sod2 and sod3 contributed much less (respectively) to the conidial UVB resistance of M. robertsii (12%, 25% and 30%) 84 than of B. bassiana (38%, 45% and 45%).…”

The carbon catabolite repressor CreA is an essential virulence factor of Metarhizium acridum against Locusta migratoria

“…Antioxidation is also an important ability of fungi to resist host immune response and the oxidative environment in hemocoele can inhibit the survival of fungi. 59 Since ΔMaCreA is sensitive to oxidants calcofluor white, Congo Red and H 2 O 2 , it is compromised to the oxidative environment in the host. Taken together, these results implied that ΔMa-CreA stimulated insect immunity earlier and stronger than the WT strain did, which may be related to the cell wall changes that help the host to quickly identify and eliminate pathogens.…”

Dsk2 involves in conidiation, multi‐stress tolerance and thermal adaptation in Beauveria bassiana

“…It has been well‐illustrated that CAT and SOD genes are responsible for oxidative stress adaptation in the typical fungus B . bassiana and Metarhizium robertsii (Chen et al ., 2016; Liu et al ., 2017; Zhang and Feng, 2018; Zhu et al ., 2018). The downregulated transcripts of three key SOD genes, one important catA gene and decreased total catalase activity are consistent with the increased sensitivity to osmotic stress.…”