Secondary metabolites, such as phenols and salicylic, play a crucial role in the regulation of development and tolerance mechanisms against a wide range of stresses. During adverse conditions such as biotic and abiotic stresses, plants induce the biosynthesis of phenolic compounds to provide tolerance. Phenolics are secondary aromatic metabolites synthesized through the shikimate/phenylpropanoid pathway or polyketide acetate/malonate pathway, which produce monomeric and polymeric phenolics. Phenolic compounds in plants not only take part in preventing stresses but also in regulating physiological activities. These compounds significantly regulate both below- and above-ground defense mechanisms. Plants synthesize thousands of phenolic compounds throughout their evolution to survive in changing environments. Environmental factors, such as high light, cold, drought, heavy metals, etc., increase the accumulation of phenolics to neutralize any toxic effects. This review focuses on the biosynthesis of phenolic compounds and their updated studies against abiotic stresses.

The phenylpropanoid pathway varies across species and environments, producing diverse metabolites. The transcriptional regulation governing precursor feeding into this pathway remains largely unexplored. Here, we characterize OscWRKY7 TF from Ocimum sanctum as a positive regulator of arogenate dehydratase-5, a key shikimate pathway gene catalyzing the conversion of arogenate into phenylalanine. Phenylalanine treatment in O. sanctum induced key genes and metabolites of the phenylpropanoid pathway, with OscWRKY7 showing early induction. Recombinant OscWRKY7 interacts with the canonical W-box cis element and transactivates the reporter gene in yeast. Ectopic expression of OscWRKY7 in Arabidopsis thaliana induced transcriptomic changes in the shikimate and phenylpropanoid pathways, leading to upregulation of arogenate dehydratase-5 transcripts and enhanced accumulation of phenylalanine and downstream metabolites. The biological function of OscWRKY7 was determined in Ocimum sanctum using gain- and loss-of-function approaches via hairy root-mediated overexpression and tobacco rattle virus (TRV)-based VIGS. Overexpression of OscWRKY7 upregulated OscADT5 and enhanced phenylalanine accumulation, along with downstream phenylpropanoid metabolites, whereas silencing reduced them, providing evidence of OscWRKY7-mediated regulation of phenylpropanoid metabolism in O. sanctum. OscWRKY7 exhibits dual cis-element specificity, binding the W-box and a noncanonical WT-box variant (TAACTTTT) in the OscADT5 promoter, suggesting a novel regulatory module. The Electrophoretic Mobility Shift Assay and the Yeast One-Hybrid Assay demonstrated binding, while dual luciferase suggests the transactivation of OscADT5 by OscWRKY7 through a noncanonical WT-box. OscWRKY7 further modulates phenylpropanoid pathway-associated genes to alter the accumulation of anthocyanin and salicylic acid, thereby enhancing plant defense response in Arabidopsis. Overall, our study suggests that OscWRKY7 promotes phenylpropanoid accumulation by facilitating the availability of phenylalanine, a precursor of the phenylpropanoid pathway.