Phenylalanine ammonia-lyase (PAL) is a crucial enzyme in the phenylpropanoid pathway, catalyzing the deamination of L-phenylalanine to trans-cinnamic acid, a precursor for various plant secondary metabolites. It plays a vital role in plant defense mechanisms, growth, and development by contributing to the biosynthesis of compounds like flavonoids, lignin, and phytoalexins.