Abstract
Fungal species belonging to the Trichoderma genus are commonly used as biocontrol agents against several crop pathogens. Among their secondary metabolites, peptaibols are helical, antimicrobial peptides, which are structurally stable even under extreme pH and temperature conditions. The promise of peptaibols as agrochemicals is, however, hampered by poor water solubility, which inhibits efficient delivery for practical use in crop protection. Using a versatile synthetic strategy, based on green chemistry procedures, we produced water-soluble analogs of the short-length peptaibol trichogin. Although natural trichogin was inactive against the tested fungal plant pathogens (Botrytis cinerea, Bipolaris sorokiniana, Fusarium graminearum, and Penicillium expansum), three analogs completely inhibited fungal growth at low micromolar concentrations. The most effective peptides significantly reduced disease symptoms by B. cinerea on common bean and grapevine leaves and ripe grape berries without visible phytotoxic effects. An in-depth conformational analysis featuring a 3D-structure–activity relationship study indicated that the relative spatial position of cationic residues is crucial for increasing peptide fungicidal activity.
Highlights
In the last decade, European Union (EU) policies have actively promoted research to reduce reliance on synthetic plant protection products (PPPs) for crop safeguarding in agricultural systems
At 50 μM, 4 reduced the infected leaf area by about 70% (Figure 5) and disease on berries by about 45% compared to the untreated control (Table 3; Figure S6, Supplementary Materials)
To make sure our substitutions did not alter the native 3D structure, we studied the conformational preferences of our trichogin analogs in solution by means of circular dichroism (CD) [44] and 2D-NMR
Summary
European Union (EU) policies have actively promoted research to reduce reliance on synthetic plant protection products (PPPs) for crop safeguarding in agricultural systems. The presence of a lipophilic acyl chain at the N-terminus makes trichogin a lipopeptaibol [28] and has been associated with inhibition of plant-pathogenic bacteria and fungi [29] This helical, mostly hydrophobic, 11-residue peptaibol is naturally produced by T. longibrachiatum, and its activity has been assayed in various biological systems [26,30,31]. In this manuscript, we describe the synthesis, conformational analysis, proteolytic resistance, and fungicidal activity of water-soluble, cationic analogs of trichogin (Table 1). All peptides were fully characterized (see Supplementary Materials) and their water solubility proven up to 0.01 M (the highest concentration tested)
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