Abstract
Insect-derived antifungal peptides have a significant economic potential, particularly for the engineering of pathogen-resistant crops. However, the nonspecific antifungal activity of such peptides could result in detrimental effects against beneficial fungi, whose interactions with plants promote growth or increase resistance against biotic and abiotic stress. The antifungal peptide metchnikowin (Mtk) from Drosophila melanogaster acts selectively against pathogenic Ascomycota, including Fusarium graminearum, without affecting Basidiomycota such as the beneficial symbiont Piriformospora indica. Here we investigated the mechanism responsible for the selective antifungal activity of Mtk by using the peptide to probe a yeast two-hybrid library of F. graminearum cDNAs. We found that Mtk specifically targets the iron-sulfur subunit (SdhB) of succinate–coenzyme Q reductase (SQR). A functional assay based on the succinate dehydrogenase (SDH) activity of mitochondrial complex II clearly demonstrated that Mtk inhibited the SDH activity of F. graminearum mitochondrial SQR by up to 52%, but that the equivalent enzyme in P. indica was unaffected. A phylogenetic analysis of the SdhB family revealed a significant divergence between the Ascomycota and Basidiomycota. SQR is one of the key targets of antifungal agents and we therefore propose Mtk as an environmentally sustainable and more selective alternative to chemical fungicides.
Highlights
Insects are well protected against pathogens by an immunity-related arsenal of effector molecules including antimicrobial peptides (AMPs)
Competent Y187 yeast cells were co-transformed with the normalized cDNA and the pGADT7-Rec vector, and the transformants were pooled after incubation for 3–5 days at 30 °C on single-dropout plates lacking leucine (SDO/–Leu)
Insect AMPs have often been shown to act against phytopathogenic fungi, and could be suitable for expression as recombinant peptides in transgenic plants to reduce yield and quality losses
Summary
Insects are well protected against pathogens by an immunity-related arsenal of effector molecules including antimicrobial peptides (AMPs). Insects produce a large number of antifungal peptides to protect them against fungal pathogens and parasites, and these peptides often interact with intracellular targets to inhibit key physiological processes such as DNA and protein synthesis, cell cycle progression and metabolic activity[1,2,3]. Whereas the activity of other antifungal peptides can affect both pathogens and beneficial endophytes, Mtk acts against pathogenic Ascomycota such as Fusarium graminearum and Blumeria graminis f. We sought additional Mtk intracellular targets by probing a yeast two-hybrid library of F. graminearum cDNAs with an artificial Mtk peptide, revealing a specific interaction with the iron-sulfur subunit (SdhB) of succinate–coenzyme Q reductase (SQR). We conducted a phylogenetic analysis of SdhB homologs in different Ascomycota and Basidiomycota to determine whether the enzyme has diverged in these two fungal phyla
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