Autophagy‐related gene BbATG11 is indispensable for pexophagy and mitophagy, and contributes to stress response, conidiation and virulence in the insect mycopathogen Beauveria bassiana

Abstract

Autophagy is a conserved degradation system in eukaryotic cells that includes non-selective and selective processes. Selective autophagy functions as a selective degradation mechanism for specific substrates in which autophagy-related protein 11 (ATG11) acts as an essential scaffold protein. In B. bassiana, there is a unique ATG11 family protein, which is designated as BbATG11. Disruption of BbATG11 resulted in significantly reduced conidial germination under starvation stress. The mutant ΔBbATG11 displayed enhanced sensitivity to oxidative stress and impaired asexual reproduction. The conidial yield was reduced by approximately 75%, and this defective phenotype could be repressed by increasing exogenous nutrients. The virulence of the ΔBbATG11 mutant strain was significantly impaired as indicated in topical and intra-hemocoel injection bioassays, with a greater reduction in topical infection. Notably, BbATG11 was involved in pexophagy and mitophagy, but these two autophagic processes appeared in different fungal physiological aspects. Both pexophagy and mitophagy were associated with nutrient shift, starvation stress and growth in the host hemocoel, but only pexophagy appeared in both oxidation-stressed cells and aerial mycelia. This study highlights that BbATG11 mediates pexophagy and mitophagy in B. bassiana and links selective autophagy to the fungal stress response, conidiation and virulence.

HapX, an Indispensable bZIP Transcription Factor for Iron Acquisition, Regulates Infection Initiation by Orchestrating Conidial Oleic Acid Homeostasis and Cytomembrane Functionality in Mycopathogen Beauveria bassiana

“…During interaction of the fungus and the host, BbHapX contributes to its almost complete virulence during topical infection and partial virulence in intrahemocoel infection. The surface of the insect cuticle is deficient in nutrients (22), whereas the host hemolymph is rich in nutrients, including FAs (e.g., oleic acid) (44). These facts readily explain why exogenous oleic acid restores partial fungal virulence during cuticle penetration and complete virulence via direct infection.…”

“…Disruption and complementation of BbHapX were accomplished as previously described (22). The gene disruption vector was constructed as follows: the upstream (1.46-kb) and downstream (1.54-kb) sequences of the BbHapX open reading frame (ORF) were amplified by PCR using the primer pairs P H 1/P H 2 and P H 3/P H 4 (see Table S1 in the supplemental material), respectively.…”

“…Phenotypic assays and feeding tests with FAs/phospholipids. Fungal phenotypes were evaluated as described previously (22).…”

“…The conidia of entomopathogenic fungi germinate on oligotrophic insect cuticles, which represent special niches of host-fungus interaction. B. bassiana is a well-investigated filamentous entomopathogenic fungus, and its conidia perform exogenous dormancy and germinate after contact with water by mobilizing its endogenous nutrients (22). B. bassiana accumulates many FAs in its conidia (23).…”

The Autophagy-Related Gene Aolatg4 Regulates Hyphal Growth, Sporulation, Autophagosome Formation, and Pathogenicity in Arthrobotrys oligospora

“…The promoter (1,345 bp) of the Aoatg8 gene in A. oligospora was amplified with the primers AoAtg8p-f and AoAtg8p-r, and the gene Aoatg8 was amplified with the primers AoAtg8-f and AoAtg8-r ( Supplementary Table S1; Ding et al, 2018). The Aoatg8 gene was integrated into the BsrGΙ sites of the Ppk2 vector, and the corresponding promoter sequence was inserted into XhoΙ; the GFP gene was cloned at the BsrGΙ and XhoΙ sites.…”