Lignin is a major impediment in the deconstruction and fractionation of plant biomass to its soluble monomeric constituents for the production of biofuels and biomaterials. Modification of the lignin biosynthetic pathway has proven to be an effective means of reducing biomass recalcitrance but can often result in impaired growth. We have previously reported the incorporation of ester-linked units into lignin backbones via lignification with monolignol ferulates in poplar and p-coumarates in Arabidopsis. The resulting poplars grow normally and have improved biomass deconstructability, especially under mild alkaline conditions that can effectively cleave the introduced ester bonds. The engineered Arabidopsis provides particularly clean evidence for such esters in lignin due to their absence in wild type. In order to further understand the structural and chemical features that may be associated with the observed improved processing efficiency, we used hyperspectral stimulated Raman scattering (hsSRS) to map the hydroxycinnamate esters in planta using lignin conjugated α–β carbon double-bonds as the proxy. Such double-bonds are present in all types of lignin, but unique structures in ester-linked lignins experience a ~20 cm-1 shift from 1650 cm-1 to 1630 cm-1 in their Raman spectra due to the conjugation between the double bond and the associated ester carbonyl group. Analysis of the hsSRS images has revealed that the Raman signal specifically representing engineered lignin can be estimated. Moreover, it exhibits a distribution pattern in cell wall layers similar to that of the native lignin, but its intensity varies in different transgenic lines. Our study suggests that both physical and chemical modification of the cell wall could contribute to the observed improvements in sugar yields.

In situ visualization of engineered lignin in plant cell walls by stimulated Raman scattering microscopy

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.