Specificity and breadth of plant specialized metabolite–microbe interactions

Plant specialized metabolites shape plant interactions with the environment including plant–microbe interactions. While we often group compounds into generic classes, it is the precise structure of a compound that creates a specific role in plant–microbe or–pathogen interactions. Critically, the structure guides definitive targets in individual interactions, yet single compounds are not limited to singular mechanistic targets allowing them to influence interactions across broad ranges of attackers, from bacteria to fungi to animals. Further, the direction of the effect can be altered by counter evolution within the interacting organism leading to single compounds being both beneficial and detrimental. Thus, the benefit of a single compound to a host needs to be assessed by measuring the net benefit across all interactions while in each specific interaction. Factoring this complexity for single compounds in plant–microbe interactions with the massive expansion in our identification of specialized metabolite pathways means that we need systematic studies to classify the full breadth of activities. Only with this full biological knowledge we can develop mechanistic, ecological, and evolutionary models to understand how plant specialized metabolites fully influence plant–microbe and plant–biotic interactions more broadly.