New Antimicrobial Agents of Plant Origin

Abstract

Plants are constantly under attack by microbial pathogens. As part of their defensive arsenal, they use antimicrobial peptides such as thionins, defensins, lipid transfer proteins, hevein-like peptides, knottins, cyclotides, b-barrelins, and others. In addition, they produce a diversity of antimicrobial metabolites. Those where the evidence for a role in plant defense is stronger include benzoxazinoids, camalexin, and glucosinolates among the alkaloids; flavonoids and stilbenes among the phenylpropanoids; and also terpenoids such as saponins. Our understanding of these plant antimicrobial agents has increased significantly in recent years with new information on their distribution, synthesis, regulation, in vivo function, and mechanism of action. Plant antimicrobial agents have a large potential for biotechnological applications. Engineered plants with increased disease resistance have been achieved using almost every family of antimicrobial peptides. There have been also been successes in using metabolic engineering to increase the production of antimicrobial compounds, as in the case of stilbenes and glucosinolates. Commercial applications using both approaches are likely to appear soon. The use of plant antimicrobials in human medicine is probably further in the future, although there are promising antifungal agents like defensin peptides, and saponins. With more than a quarter million species and a particularly diverse specialized metabolism, the richness of plant antimicrobials has barely been explored. Plant Antimicrobial DefensesWild plants are quite successful at keeping bacterial and fungal pathogens at bay. In addition to physical barriers, they have an immune system capable of detecting and responding to the presence of pathogens. The first layer of defense is based on

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