Enhancing monolignol ferulate conjugate levels in poplar lignin via OsFMT1

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Abstract Background The phenolic polymer lignin is one of the primary chemical constituents of the plant secondary cell wall. Due to the inherent plasticity of lignin biosynthesis, several phenolic monomers have been shown to be incorporated into the polymer, as long as the monomer can undergo radicalization so it can participate in coupling reactions. In this study, we significantly enhance the level of incorporation of monolignol ferulate conjugates into the lignin polymer to improve the digestibility of lignocellulosic biomass. Results Overexpression of a rice Feruloyl-CoA Monolignol Transferase (FMT), OsFMT1, in hybrid poplar (Populus alba x grandidentata) produced transgenic trees clearly displaying increased cell wallbound ester-linked ferulate, p-hydroxybenzoate, and p-coumarate, all of which are in the lignin cell wall fraction, as shown by NMR and DFRC. We also demonstrate the use of a novel UV-Vis spectroscopy technique to rapidly screen plants for the presence of both ferulate and phydroxybenzoate esters. Lastly, we show via saccharification assays, that the OsFMT1 transgenic poplars have significantly improved processing efficiency compared to wild-type poplars as well as AsFMT poplars Conclusions The findings demonstrate that OsFMT1 has a broad substrate specificity and a higher catalytic efficiency compared to the previously published FMT from Angelica sinensis (AsFMT). Importantly, the increased processing efficiency makes OsFMT1 a promising gene to optimize the composition of lignocellulosic biomass.

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