Innate Immunity in Plants: The Role of Antimicrobial Peptides

Abstract

Antimicrobial peptides (AMPs) are part of innate immunity, establishing a first line of defense against pathogens. All plant organs express AMPs constitutively or in response to microbial challenges. Plant AMPs are structurally and functionally diverse. Five classes of AMPs are considered in this review, the thionins, defensins, lipid transfer proteins (LTPs), snakins, and a group of related knottins, cyclotides and hevein-like AMPs. Besides targeting fungal, bacterial, and oomycete pathogens, certain AMPs can be directed against other organisms, like herbivorous insects. The biological activity of plant AMPs primarily depends on interactions with membrane lipids, but other modes of action exist as in the case of defensins with α-amylase activity or a defensin-like peptide that interacts with a receptor kinase. Limited information exists on the regulated expression of plant AMPs, their processing, and posttranslational modification. Conclusive data on the role of certain AMPs in plant defense have only recently become available. This review can therefore only be considered as a snapshot of the progress in this field of research.