phenylpropanoid

Phenylpropanoid refers to a broad class of plant secondary metabolites derived from the phenylpropanoid pathway, characterized by a phenylpropane skeleton. The phenylpropanoid family includes phenolic acids, flavonoids, stilbenes, lignans, and lignin. These compounds occur throughout plants and participate in growth, development, defense, and interactions with the environment.

Biosynthesis begins with phenylalanine and the enzyme phenylalanine ammonia-lyase (PAL), which produces cinnamic acid. Cinnamic acid is hydroxylated by C4H to form p-coumaric acid. Activation by 4CL yields p-coumaroyl-CoA, a branching point that leads to lignin precursors (monolignols) and flavonoid biosynthesis through distinct enzyme sets. Enzymes such as HCT, C3H, COMT, CCoAOMT, CCR, and CAD catalyze steps that produce lignin monomers, while chalcone synthase and related enzymes drive flavonoid formation. The pathway thus gives rise to a diverse array of compounds sharing the hydroxycinnamoyl core.

Roles in plants include structural support and water transport via lignin, protection against ultraviolet radiation, pigmentation, and defense against pathogens and herbivores. Phenylpropanoids influence flower coloration, seed dispersal, and signaling with other organisms. In humans, dietary phenylpropanoids contribute antioxidants and observed health benefits, though effects vary by compound and dose. Industrially, lignin is a major byproduct of wood processing and a potential feedstock for bio-based materials, while other phenylpropanoids serve as flavors, dyes, or chemical precursors. Regulation of the pathway integrates developmental cues and environmental stress, making it a focal point in studies of plant metabolism and biotechnology.