Genetic variation and modes of action of secondary metabolites in plant stress responses and ecological interactions

Secondary metabolites contribute to plant stress adaptation through genetically controlled variation in abundance and composition, direct effects on physiological processes, and interactions with other organisms. Here, we review the criteria and mechanistic evidence for regulatory roles of secondary metabolites and the genetic basis of natural variation in their abundance and composition. We highlight experimental findings for their effects on plant responses to biotic and abiotic stresses, as well as the mechanisms by which exuded and volatile metabolites shape interactions with microbes and herbivores. Although genetic mapping identifies metabolite-associated loci and their functions have been documented, direct evidence linking natural alleles to metabolite-mediated stress responses remains scarce. Establishing these links is key to understanding plant stress adaptation and prioritizing candidate loci for crop improvement. Progress will require evaluating metabolite-associated alleles across contrasting environments together with experimental validation of the corresponding metabolite effects.