Insect peptide metchnikowin confers on barley a selective capacity for resistance to fungal ascomycetes pathogens

Abstract

The potential of metchnikowin, a 26-amino acid residue proline-rich antimicrobial peptide synthesized in the fat body of Drosophila melanogaster was explored to engineer disease resistance in barley against devastating fungal plant pathogens. The synthetic peptide caused strong in vitro growth inhibition (IC50 value ∼1 μM) of the pathogenic fungus Fusarium graminearum. Transgenic barley expressing the metchnikowin gene in its 52-amino acid pre-pro-peptide form under the control of the inducible mannopine synthase (mas) gene promoter from the Ti plasmid of Agrobacterium tumefaciens displayed enhanced resistance to powdery mildew as well as Fusarium head blight and root rot. In response to these pathogens, metchnikowin accumulated in plant apoplastic space, specifying that the insect signal peptide is functional in monocotyledons. In vitro and in vivo tests revealed that the peptide is markedly effective against fungal pathogens of the phylum Ascomycota but, clearly, less active against Basidiomycota fungi. Importantly, germination of the mutualistic basidiomycete mycorrhizal fungus Piriformospora indica was affected only at concentrations beyond 50 μM. These results suggest that antifungal peptides from insects are a valuable source for crop plant improvements and their differential activities toward different phyla of fungi denote a capacity for insect peptides to be used as selective measures on specific plant diseases.

Antimicrobial peptides

“…2 Assessment of metchnikowin effects on powdery mildew fungus during its interaction with transgenic barley provided evidence that the antifungal peptide improves the resistance of plant as if it impedes the development of functional haustorium due to increased rate of hypersensitive response (HR) and development of cell wall apposition (CWA). 2 Comprehensive study on possible latent influence of metchnikowin on the defense system of plant revealed that the SAR and ISR pathways as well as redox status of metchnikowin-expressing barley plants are potentiated during interaction with powdery mildew fungus. 99 In Phenylpropanoid pathway, the PAL-1 gene expression profile demonstrated that in Bgh challenge the activity of phenylalanine ammonia-lyase is elevated in metchnikowin transgenic plants.…”

“…2 Despite the fact that the definite cause for specificity has not been elucidated yet, these observations do prospect a promising approach: utilizing AMPs to diminish the devastating consequences of diseases and pests without affecting the plant's essential mutualistic interactions with beneficial symbionts. Clearly, these symbionts are of vital importance for plants in terms of presenting a better fitness via supporting water and mineral uptake as well as strengthening disease resistance.…”

“…[1][2][3] They might additionally have the ability to boost the host immunity by functioning as immunomodulators. 4,5 Plenty of AMPs exist to cope with practically all potential infection sources.…”

“…In general, the amphipathic peptides consist of positively charged residues, predominantly arginine and lysine, or else histidine in acidic setting, and a substantial ratio of hydrophobic amino acids. 6,7 The best-known antimicrobial peptide families are (1) linear α-helical peptides comprising cecropins 8 and magainins 9 exhibiting generally antibacterial activities, (2) multiple Cystein-bridge-containing defensins showing antibacterial and antifungal activities, 10,11 (3) Pro-rich peptides with activity against bacteria and filamentous fungi, 2,12 and (4) the Gly-rich peptides active mainly against Gram-negative and occasionally Gram-positive bacteria. 13,14 Correspondence to: Mohammad Rahnamaeian; Email: Rahnamaeian@mail.uk.ac.ir Submitted: 04/29/11; Revised: 05/21/11; Accepted: 05/23/11 DOI: 10.4161/psb.…”

“…33 These peptides, predominantly found in Class Insecta, are active against bacteria and fungi. 2,37 The most recognized small Pro-rich AMPs are apidaecins that structurally consist of two domains: the conserved domain in charge of general antibacterial activity, and the variable one responsible for the antibacterial spectrum. They are lethal to many Gram-negative bacteria.…”