Evolution of p‐coumaroylated lignin in eudicots provides new tools for cell wall engineering

• Published in: The New phytologist Vol. 237; no. 1; pp. 251 - 264
• Main Authors: Mottiar, Yaseen, Smith, Rebecca A., Karlen, Steven D., Ralph, John, Mansfield, Shawn D.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.01.2023; Wiley; John Wiley and Sons Inc
• Subjects: acylated lignin; Acyltransferase; Acyltransferases - metabolism; Alcohols; Amino acids; BAHD monolignol acyltransferase; BASIC BIOLOGICAL SCIENCES; Cell Wall - metabolism; Cell walls; cell-wall-bound phenolics; Coenzyme A - analysis; Coenzyme A - metabolism; convergent evolution; designer lignins; Engineering; Evolution; Fibers; Hardwoods; Hibiscus cannabinus; Kenaf; Lignin; Lignin - metabolism; p-coumarate pendent groups; plant cell walls; Polymerization; Poplar; Populus - metabolism; Recombinants; Saccharification; Sinapyl alcohol; Substrates; Vegetable fibers; cell-wall-bound phenolics; BAHD monolignol acyltransferase; acylated lignin; convergent evolution; plant cell walls; designer lignins; p-coumarate pendent groups
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.18518

Summary Ester‐linked p‐coumarate (pCA) is a hallmark feature of the secondary cell walls in commelinid monocot plants. It has been shown that pCA groups arise during lignin polymerisation from the participation of monolignol conjugates assembled by p‐coumaroyl‐CoA:monolignol transferase (PMT) enzymes, members of the BAHD superfamily of acyltransferases. Herein, we report that a eudicot species, kenaf (Hibiscus cannabinus), naturally contains p‐coumaroylated lignin in the core tissues of the stems but not in the bast fibres. Moreover, we identified a novel acyltransferase, HcPMT, that shares <30% amino acid identity with known monocot PMT sequences. Recombinant HcPMT showed a preference in enzyme assays for p‐coumaroyl‐CoA and benzoyl‐CoA as acyl donor substrates and sinapyl alcohol as an acyl acceptor. Heterologous expression of HcPMT in hybrid poplar trees led to the incorporation of pCA in lignin, but no improvement in the saccharification potential of the wood. This work illustrates the value in mining diverse plant taxa for new monolignol acyltransferases. Furthermore, the occurrence of pCA outside monocot lineages may represent another example of convergent evolution in lignin structure. This discovery expands textbook views on cell wall biochemistry and provides a new molecular tool for engineering the lignin of biomass feedstock plants.