Characterization of the Hog1 MAPK pathway in the entomopathogenic fungus Beauveria bassiana

Abstract

High-osmolarity glycerol (HOG) pathway required for yeast osmoregulation relies upon the mitogen-activated protein kinase (MAPK) Hog1 cascade that comprise the MAPKKKs Ssk2/Ssk22 and Ste11 converging on the MAPKK Pbs2. Here we show a Hog1 cascade with the unique MAPKKK Ssk2 acting in Beauveria bassiana. Hypersensitivity to high osmolarity and high resistance to fludioxonil fungicide appeared in Δssk2, Δpbs2 and Δhog1 mutants whereas the two hallmark phenotypes were reversed in Δste11. Increased sensitivity to heat shock and decreased sensitivity to cell wall perturbation also occurred in the three mutants but not in Δste11 although antioxidant phenotypes were different in all deletion mutants. Intriguingly, signals of Hog1 phosphorylation induced by osmotic, oxidative and thermal cues were present in Δste11 but absent in Δssk2 and Δpbs2. Moreover, vegetative growth on minimal media with different carbon/nitrogen sources was much more suppressed in Δste11 and Δssk2 than in Δpbs2 and Δhog1 although all mutants suffered similar, but severe, conidiation defects on a standard medium. Normal host infection was abolished in Δste11 while virulence was differentially attenuated in other mutants. Our findings exclude Ste11 from the Hog1 cascade that regulates multiple stress responses and environmental adaptation of B. bassiana and perhaps other filamentous fungi.

Essential role of Rpd3‐dependent lysine modification in the growth, development and virulence of Beauveria bassiana

“…Intriguingly, 31 differentially expressed proteins and 44 modified Kac proteins were associated with the development of sexual spores, which never form in the teleomorph‐free WT strain studied. In contrast, only one protein with a single modified Kac site was involved in the formation of hyphae [putative histidine kinase NIK1p (J4KR52), i.e., HK3 (EJP70349) characterized as a regulator of conidiation and stress response by Liu and colleagues ()] or the development of conidia [conidiation‐specific protein Con‐13 (J4WEL0), functionally unknown yet]. Thus, the proteomic/acetylomic data revealed little evidence for the essential role of Rpd3 in the asexual development of B. bassiana , as unveiled by the drastic repression of conidiation in Δ rpd3 .…”

AoStuA, an APSES transcription factor, regulates the conidiation, trap formation, stress resistance and pathogenicity of the nematode‐trapping fungus Arthrobotrys oligospora

“…The conidial yields of the fungal strains were determined as previously described (Liu et al ., ; Yang et al ., ). Three cultures (replicates) for each strain were initiated by spreading a 100‐μL aliquot of a 10 5 conidia mL −1 suspension per CMY plate, followed by 10 days of incubation at 28°C.…”

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

“…The essential role of Wsc1I in the fungal responses to osmotic, oxidative, cell wall perturbing stresses suggests its possible link to the stress‐responsive MAPK cascades. This speculation is validated by expressed and phosphorylated Hog1 levels, which were detected in the protein extracts from the hyphal cells of Δ wsc1I and its control strains through Western blot hybridization as described previously (Liu, Wang, et al, ). The expressed Hog1 signals detected by anti‐Hog1p C‐terminus antibody were similar in the hyphal extracts of all tested strains exposed for 60 min to sorbitol (1 M), NaCl (0.8 M), H 2 O 2 (4 mM), and calcofluor white (5 μg ml −1 ), respectively, or not exposed and also similar to the corresponding blots of expressed glyceraldehyde 3‐phosphate dehydrogenase (GAPDH) used as an internal standard (middle and lower panels in Figure d).…”

“…The Δ wsc1I mutant also became sensitive or hypersensitive to Cu 2+ , Zn 2+ , Fe 2+ , and Mg 2+ during colony growth and suffered marked reductions in conidial thermotolerance and UVB resistance. Interestingly, these phenotypes were generally more defective in the absence of Wsc1I than of each of Wsc1A–E or VLP1–3 (Tong, Chen, Ying, & Feng, ; Tong, Chen, Zhu, et al, ) and not necessarily linked to the MAPK cascades except the Hog1 phosphorylation triggered by heat shock (Liu, Wang, et al, ). Particularly, cell sensitivity to Cu 2+ was unaffected in the previous single‐gene deletion mutants of VLP1–3 .…”

“…The Sho1 branch was rarely shown to function in filamentous fungal osmoregulation. The non‐essentiality has been clarified in B. bassiana (Liu, Wang, Sun, Ying, & Feng, ), a filamentous fungal insect pathogen that usually undergoes asexual cycle, has the broadest host spectrum, and serves as one of main sources of fungal insecticides (Tong & Feng, ).…”