Transcriptomic insights into the alternative splicing‐mediated adaptation of the entomopathogenic fungus Beauveria bassiana to host niches: autophagy‐related gene 8 as an example

Abstract

Alternative splicing (AS) regulates various biological processes in fungi by extending the cellular proteome. However, comprehensive studies investigating AS in entomopathogenic fungi are lacking. Based on transcriptome data obtained via dual RNA-seq, the first overview of AS events was developed for Beauveria bassiana growing in an insect haemocoel. The AS was demonstrated for 556 of 8840 expressed genes, accounting for 5.4% of the total genes in B. bassiana. Intron retention was the most abundant type of AS, accounting for 87.1% of all splicing events and exon skipping events were rare, only accounting for 2.0% of all events. Functional distribution analysis indicated an association between alternatively spliced genes and several physiological processes. Notably, B. bassiana autophagy-related gene 8 (BbATG8), an indispensable gene for autophagy, was spliced at an alternative 5' splice site to generate two transcripts (BbATG8-α and BbATG8-β). The BbATG8-α transcript was necessary for fungal autophagy and oxidation tolerance, while the BbATG8-β transcript was not. These two transcripts differentially contributed to the formation of conidia or blastospores as well as fungal virulence. Thus, AS acts as a powerful post-transcriptional regulatory strategy in insect mycopathogens and significantly mediates fungal transcriptional adaption to host niches.

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

“…During proliferation in the hemocoel cavity, fungal cells are oxidatively stressed by ROS from the immune defence in the host (Bergin et al, 2005). In addition to pexophagy, mitophagy also occurs in in vivo hyphal bodies, which float in the host hemolymph for several days (Dong et al, 2017). This result suggests that mitophagy in in vivo hyphal bodies might be induced by chronic oxidative stress; however, more studies are needed to reveal the detailed inducing factors from the complicated host niches.…”

“…To evaluate the role of BbATG11 in B. bassiana, phenotypic assays were performed among the wild-type, disruption and complementation strains as described previously (Ying et al, 2014;Dong et al, 2017).…”

“…All the fungal samples were cultured and prepared as previously described (Ying et al, 2014;Dong et al, 2017).…”

Transcriptomic analyses reveal comprehensive responses of insect hemocytes to mycopathogen Beauveria bassiana, and fungal virulence-related cell wall protein assists pathogen to evade host cellular defense

“…The surviving larvae were sampled at the indicated time-points and bled. The hemolymph was immediately mixed with anticoagulant solution (0.14 M NaCl, 0.1 M glucose, 26 mM citric acid, 30 mM trisodium citrate, 10 mM EDTA, pH 4.6) [3]. The host hemocytes were collected via centrifuging, and kept on ice.…”

“…The parasitic processes of EPF involve following basic phases: spore adhesion to host, germination on cuticle surface, penetration through exoskeleton, colonization in hemocoel, and sporulation on the mycosed cadavers [ 2 ]. Successful colonization and propagation are essential for fungal virulence [ 3 ], but may be limited by the host immune defenses [ 4 ].…”