Characterization of a fungal competition factor: Production of a conidial cell-wall associated antifungal peptide

Abstract

Competition is one of the fundamental driving forces of natural selection. Beauveria bassiana is a soil and plant phylloplane/root fungus capable of parasitizing insect hosts. Soil and plant environments are often enriched with other fungi against which B. bassiana competes for survival. Here, we report an antifungal peptide (BbAFP1), specifically expressed and localized to the conidial cell wall and is released into the surrounding microenvironment inhibiting growth of competing fungi. B. bassiana strains expressing BbAFP1, including overexpression strains, inhibited growth of Alternaria brassicae in co-cultured experiments, whereas targeted gene deletion of BbAFP1 significantly decreased (25%) this inhibitory effect. Recombinant BbAFP1 showed chitin and glucan binding abilities, and growth inhibition of a wide range of phytopathogenic fungi by disrupting membrane integrity and eliciting reactive oxygen species (ROS) production. A phenylalanine residue (F 50) contributes to chitin binding and antifungal activity, but was not required for the latter. Expression of BbAFP1 in tomato resulted in transgenic plants with enhanced resistance to plant fungal pathogens. These results highlight the importance of fungal competition in shaping primitive competition strategies, with antimicrobial compounds that can be embedded in the spore cell wall to be released into the environment during the critical initial phases of germination for successful growth in its environmental niche. Furthermore, these peptides can be exploited to increase plant resistance to fungal pathogens.

Entomopathogenic fungi decreaseRhizoctoniadisease in potato in field conditions

“…These suggestions have been confirmed in experiments involving cell-free culture filtrates (Renwick, Campbell & Coe, 1991;Bark et al, 1996;Sasan & Bidochka, 2013;Lozano-Tovar et al, 2017). It was also shown that B. bassiana produces an antifungal peptide (BbAFP1) that inhibits the growth of Alternaria brassicae (Tong et al, 2020). The activity of Metarhizium extracts against Phytophthora sojae and Aphanomyces cochlioides was associated with the secondary metabolites aurovertins and fungerin, N-(methyl-3-oxodec-6-enoyl)-2-pyrroline, and N-(methyl-3-oxodecanoyl)-2-pyrroline (Putri et al, 2014).…”

The Antifungal Protein AfpB Induces Regulated Cell Death in Its Parental Fungus Penicillium digitatum

“…Altogether, these results suggest that mannoproteins determine AfpB interaction with the cell wall and, thus, its antifungal activity. (29,(31)(32)(33)(34). ROS production was monitored in these studies after long and high-concentration treatments, with deleterious effects observed; it was unclear whether ROS was signaling or a consequence of cell death.…”

“…The generation of reactive oxygen species (ROS) is associated with cell death, acting either as signaling molecules in regulated cell death or as toxic compounds causing oxidative damage to lipids, proteins, and nucleic acids and uncontrolled cell destruction. Several studies have previously reported the production of ROS in fungal cells triggered by AFPs ( 29 , 31 – 34 ). ROS production was monitored in these studies after long and high-concentration treatments, with deleterious effects observed; it was unclear whether ROS was signaling or a consequence of cell death.…”

Interplay between Fungal Infection and Bacterial Associates in the Wax Moth Galleria mellonella under Different Temperature Conditions

“…It is important to note that entomopathogenic fungi produce various secondary metabolites and enzymes (oosporeins, destruxins, different proteinases, AMPs) for inhibiting both host immune responses and competitive microorganisms [ 36 , 48 , 49 ]. The set of enzymes and secondary metabolites present is significantly different between fungal species and depends on host and habitat specificity.…”