Functional Divergence of the PAL Gene Family in Salt and Cadmium Stress Responses of Populus alba

ABSTRACT Phenylalanine ammonia‐lyase (PAL) is the rate‐limiting enzyme initiating the phenylpropanoid metabolic pathway and plays a central role in regulating plant secondary metabolism and stress responses. In this study, five PoalbPAL genes were identified from the Populus alba genome through genome‐wide analysis. Enzyme kinetic assays demonstrated catalytic activity in PoalbPAL1 , 2 , 4 , and 5 , with notable differences in catalytic efficiency, whereas PoalbPAL3 was catalytically inactive. Transcriptome and metabolome integrative analysis revealed that PoalbPAL1 , 2 , and 5 were coordinately upregulated under salt stress, channeling phenylpropanoid metabolism toward flavonoid biosynthesis and promoting the accumulation of antioxidant metabolites such as naringenin. In contrast, cadmium stress rapidly activated PoalbPAL2 and PoalbPAL5 , preferentially directing metabolic flux toward lignin monomer synthesis, thereby restricting Cd 2+ influx through cell wall reinforcement. Heterologous expression in yeast further validated the functional divergence of PoalbPAL members in response to salt and cadmium stress. This study reveals the functional divergence of PAL gene family members in coordinating distinct phenylpropanoid metabolic responses to salt and cadmium stress, providing valuable gene resources and theoretical insights for genetic improvement of stress resistance in woody plants.