A learning landscape of flavonoids in plant stress adaptation

Flavonoids constitute a diverse class of plant secondary metabolites with profound biological and economic value, especially for plant stress adaptation. As ubiquitously distributed polyphenolic compounds in the plant kingdom, flavonoids predominantly exist as glycosylated derivatives (flavonoid glycosides) or as free aglycones in fruits, vegetables, legumes, and tea species. In response to diverse abiotic and biotic stresses, plants accumulate specific flavonoids to modulate core physiological defense responses, including stress signal regulation, pigment-mediated environmental acclimation, and pathogen resistance. Additionally, mounting evidence supports their therapeutic potential for human health applications. Plant domestication has exerted substantial selective pressure on flavonoid biosynthetic pathways, leading to extensive genomic variations and altered gene expression patterns that reshape plant stress adaptability. These evolutionary adaptations reflect the dual constraints of natural selection for enhanced stress tolerance and artificial selection targeting improved crop nutritional performance. This review comprehensively summarizes advances in the diversity, biological functions, and stress-adaptive roles of flavonoids across model organisms and economically valuable crops. We critically examine the genetic basis of stress-triggered natural variation in flavonoid metabolism and discuss modern biotechnological strategies for directionally improving the accumulation of stress-responsive flavonoids in crops. Furthermore, we evaluate emerging methodologies, such as transcriptomics, metabolomics, genome-wide association studies (GWAS), and CRISPR, for flavonoid discovery and characterization, providing strategic recommendations for advancing the development and commercial exploitation of stress-resistant, plant-derived flavonoid compounds with functional applications.