Monolignol acyltransferase for lignin p -hydroxybenzoylation in Populus

Plant lignification exhibits notable plasticity. Lignin in many species, including Populus spp., has long been known to be decorated with p -hydroxybenzoates. However, the molecular basis for such structural modification remains undetermined. Here, we report the identification and characterization of a Populus BAHD family acyltransferase that catalyses monolignol p -hydroxybenzoylation, thus controlling the formation of p -hydroxybenzoylated lignin structures. We reveal that Populus acyltransferase PHBMT1 kinetically preferentially uses p -hydroxybenzoyl-CoA to acylate syringyl lignin monomer sinapyl alcohol in vitro. Consistently, disrupting PHBMT1 in Populus via CRISPR–Cas9 gene editing nearly completely depletes p -hydroxybenzoates of stem lignin; conversely, overexpression of PHBMT1 enhances stem lignin p -hydroxybenzoylation, suggesting PHBMT1 functions as a prime monolignol p -hydroxybenzoyltransferase in planta. Altering lignin p -hydroxybenzoylation substantially changes the lignin solvent dissolution rate, indicative of its structural significance on lignin physiochemical properties. Identification of monolignol p -hydroxybenzoyltransferase offers a valuable tool for tailoring lignin structure and physiochemical properties and for engineering the industrially important platform chemical in woody biomass.