Tryptophan metabolism and plant health: mechanisms of action and application prospects.

Pathogen infection poses a severe threat to the global crop yield and quality. Recent studies have highlighted the pivotal role of tryptophan and its metabolites in regulating plant disease resistance. However, owing to the highly branched nature of the tryptophan metabolic network and the functional pleiotropy of its products, the mechanisms by which these metabolites influence plant health have yet to be systematically elucidated. To address this gap, this review first summarizes the biosynthesis and metabolic routing of tryptophan in both plants and microorganisms, along with the key regulatory factors governing these processes. Building on this foundation, we elaborate on the multifaceted mechanisms through which tryptophan and its derivatives regulate plant health, including direct pathogen inhibition, reshaping of the soil microbiome, strengthening of cell wall physical barriers, crosstalk with reactive oxygen/nitrogen species (ROS/RNS), interactions with plant hormones, as well as induction of defense gene expression. Eventually, there is an in-depth discussion about the application prospects and major challenges of leveraging tryptophan metabolites in agricultural development. Altogether, our overarching goal is to establish a theoretical framework and chart new investigative avenues for fostering sustainable plant protection strategies and improving crop resilience. Systematic review registration: https://orcid.org/0009-0008-8550-2347.