Flavonoids across biological kingdoms: biosynthetic diversity and applications in agriculture and human nutrition/health

Flavonoids are multifunctional natural products classically associated with plants, whereas bacteria, fungi, and algae have not traditionally been considered flavonoid producers through the canonical phenylpropanoid pathway. Extensive evidence documents the dietary importance of flavonoids as nutraceuticals—particularly anthocyanins, anthocyanidins, and isoflavones, and their anti-inflammatory, antibacterial, and anticancer activities. Their amenability to structural modification has further enabled the development of flavonoid-derived therapeutics, while compounds such as luteolin, and quercetin function as potent antioxidants and reactive oxygen species (ROS) scavengers, underscoring their expanding clinical and industrial relevance. Beyond nutrition and medicine, flavonoids play central signaling roles in legume–rhizobia symbioses, plant-pathogen interactions, and parasite–host dynamics, thereby shaping soil health and ecosystem functioning. Here, we review recent advances in plant flavonoid biosynthesis and emerging evidence for flavonoid production or flavonoid-like metabolic capacity in select bacteria, algae, and fungi—organisms not traditionally recognized as flavonoid producers. We highlight progress in genome editing, multi-omics, synthetic biology, and AI-assisted pathway reconstruction that has accelerated the discovery of novel flavonoids and refined our understanding of their therapeutic potential. By integrating molecular, physiological, and translational perspectives, we propose a unified framework to guide future research aimed at accelerating flavonoid applications in agriculture and improving human nutrition and health.