Insight into vital role of autophagy in sustaining biological control potential of fungal pathogens against pest insects and nematodes

Abstract

Autophagy is a conserved self-degradation mechanism that governs a large array of cellular processes in filamentous fungi. Filamentous insect and nematode mycopthogens function in the natural control of host populations and have been widely applied for biological control of insect and nematode pests. Entomopathogenic and nematophagous fungi have conserved "core" autophagy machineries that are analogous to those found in yeast but also feature several proteins involved in specific aspects of the autophagic pathways. Here, we review the functions of autophagy in protecting fungal cells from starvation and stress cues and sustaining cell differentiation, asexual development and virulence. An emphasis is placed upon the regulatory mechanisms involved in autophagic and non-autophagic roles of some autophagy-related genes. Methods used for monitoring conserved or specific autophagic events in fungal pathogens are also discussed.

Keywords: Entomopathogenic fungi; asexual development; autophagic events; host-pathogen interactions; nematophagous fungi; stress response; virulence.

Figure 1.

Autophagy-related (ATG) genes functioning in unicellular fungi. Forty-two ATG genes plus Vps14 and Vps34 involved in autophagy pathway of yeast species are sorted into two groups, of which one works in the “core” autophagy machinery and another participates in various specific pathways [24].

Figure 2.

Overview of autophagic events in entomopathogenic and nematophagous fungi. (A) Divergent roles of autophagic events in sustaining the in vitro and in vivo cellular processes of B. bassiana, M. robertsii and A. oligospora, three representative mycopathogens that have evolved for adaptation to distinct host spectra and associated habitats and fall into different lineages. Autophagy mediates the asterisked process that is distinct for each of the fungal pathogens to penetrate through the host cuticle after conidial germination. (B) Transmission electronic microscopic images (scale bars: 0.2 μm) for intravacuolar autophagic events altered by singular deletions of ATG1, ATG5, ATG8 and ATG11 in B. bassiana. (C) Proposed model for autophagy pathways in B. bassiana, including starvation-induced or non-selective autophagy, selective autophagy and bulk autophagy. PE: phosphatidylethanolamine.