The <scp>BAHD</scp> Acyltransferase Gene Family: Evolutionary Dynamics, Biochemical Mechanisms, and Roles in Plant Stress Adaptation

BAHD acyltransferases constitute one of the most versatile enzyme superfamilies in plants, catalysing the acylation of alcohols, amines, polyamines, and phenolic compounds to generate an extraordinary diversity of specialised metabolites. Initially identified through a limited number of anthocyanin- and alkaloid-modifying enzymes, BAHDs are now recognised as key regulators of phenylpropanoid flux, cutin and suberin polymerisation, volatile ester biosynthesis, and the stabilisation of acylated flavonoids. Comparative genomic analyses classify BAHD proteins into eight clades that share conserved catalytic motifs yet display pronounced functional divergence, reflecting a balance between deep evolutionary conservation and lineage-specific innovation. Recent structural and biochemical studies demonstrate how subtle active-site modifications govern substrate promiscuity and specialisation, enabling rapid metabolic reprogramming during environmental stress. Omics-based investigations further reveal widespread induction of BAHD genes under drought, salinity, heat stress, pathogen attack, and herbivory, linking BAHD activity to cell wall reinforcement, phenolamide biosynthesis, anthocyanin acylation, and ecological signalling. Beyond their physiological roles, BAHD acyltransferases have emerged as attractive targets for metabolic engineering, synthetic biology, and crop improvement, where manipulation of specific family members enhances stress tolerance, biomass quality, and nutritional or industrial value. Here, we integrate evolutionary, structural, and regulatory insights into BAHD function, highlight emerging translational opportunities, and discuss challenges associated with functional redundancy, substrate promiscuity, and biosafety considerations. Collectively, this synthesis positions BAHD acyltransferases as central mediators of plant adaptation and as promising tools for sustainable agriculture and biotechnological innovation.