Antimicrobial peptides: modes of mechanism, modulation of defense responses

Abstract

Complicated schemes of classical breeding and their drawbacks, environmental risks imposed by agrochemicals, decrease of arable land, and coincident escalating damages of pests and pathogens have accentuated the necessity for highly efficient measures to improve crop protection. During co-evolution of host-microbe interactions, antimicrobial peptides (AMPs) have exhibited a brilliant history in protecting host organisms against devastation by invading pathogens. Since the 1980s, a plethora of AMPs has been isolated from and characterized in different organisms. Nevertheless the AMPs expressed in plants render them more resistant to diverse pathogens, a more orchestrated approach based on knowledge of their mechanisms of action and cellular targets, structural toxic principle, and possible impact on immune system of corresponding transgenic plants will considerably improve crop protection strategies against harmful plant diseases. This review outlines the current knowledge on different modes of action of AMPs and then argues the waves of AMPs’ ectopic expression on transgenic plants’ immune system.

Figure 1

Schematic illustration of three pore-forming mechanisms to explain the α-helical membrane peptides. In “toroidal” model, the peptide builds toroidal pores in lipid bilayers. Pore construction is managed by the lipid polar head groups and the helix bundles that orient vertically to the membrane exterior. In other words, the attached peptides aggregate and tempt the lipid monolayers to bend continuously through the pore so that both the inserted peptides and the lipid head groups line the water core. “Carpet-like” mechanism refers to destruction of membrane assembly by collaborative action of peptides. Peptides self-associate onto the acidic phospholipids-rich regions of lipid bilayers, and as soon as their concentrations reach to a certain threshold, they permeate into the membrane. This is assisted by escalating the positive potential of bilayer. Via “barrel-stave” mechanism, peptide inserts into the membrane hydrophobic substance, flips inward and creates a pore by forming transmembrane helical bundles. (Scheme is modified after refs. and 46).