Role of Plant Secondary Metabolites at the Host–Pathogen Interface

Abstract

Plants synthesise and accumulate a large number of structurally diversified small molecules, usually derived from amino acids or some other end products or intermediates of plant primary metabolism. Some groups of these ‘secondary metabolites’ possess in vitro antimicrobial activities, typically through inhibition of essential microbial enzyme activities or disintegration of cellular compartments. This suggests a potential functional significance of plant secondary products as executors of plant immune responses. Consistent with this, impairment of the capacity of pathogens to metabolise/detoxify such compounds often increases virulence. Defence‐related phytochemicals are often classified on the basis of their in planta mode of biosynthesis and accumulation as phytoalexins or phytoanticipins. Their synthesis and/or activation are typically coordinated in time and space with other defence responses upon microbial colonisation attempts. Single plant cells are capable to target resistance responses with subcellular precision to incipient microbial entry sites. One function of this process appears to enable high local concentrations of toxic metabolites. Traditional plant breeding revealed that disease resistance correlates in some cases positively with the ability of plants to synthesise particular secondary products. This is corroborated by transgenic plants that fail to either accumulate phytoalexins or synthesise novel pathogen‐inducible toxic metabolites.

A pattern-triggered immunity-related phenolic, acetosyringone, boosts rapid inhibition of a diverse set of plant pathogenic bacteria

“…Our results add a new aspect to the types of of antimicrobial activities found in plants. Direct antimicrobial activity of metabolites derived from plants have been widely investigated (reviewed in [49]). Antimicrobial activity of ROS in plants has long been studied as well [50,51].…”