General Phenylpropanoid Metabolism: Regulation By Environmental and Developmental Signals

Abstract

A tremendous array of plant natural products is synthesized from Lphenylalanine via a series of biosynthetic pathways involving phenylpropanoid metabolism. Phenylpropanoid metabolism can be divided into a central, general pathway (“general phenylpropanoid metabolism”), required for the synthesis of all phenylpropanoid metabolites, and specific branch pathways emanating from the general pathway which may require in addition other pathways. These lead to the synthesis of specific phenolic end products (Fig. 1). Phenylalanine ammonia-lyase (PAL) catalyzes the first step of general phenylpropanoid metabolism, the deamination of L-phenylalanine to produce cinnamic acid. Cinnamic acid is hydroxylated by cinnamate 4-hydroxylase (C4H) to yield 4coumaric acid. The activities of hydroxylases and 0-methyl transferases upon 4coumaric acid can yield derivatives of 4-coumaric acid (e.g. ferulic acid, 3’ methoxylated, and sinapic acid, 3’,5’ methoxylated). The enzyme 4-coumarate: CoA ligase (4CL) catalyzes the third and final step in the general pathway, the formation of activated CoA esters of hydroxycinnamic acids (4-coumaric acid or its methoxylated derivatives).