Precursor-Dependent Lignin Biosynthesis in Grasses Revealed by DNP-Enhanced Solid-State NMR

Priya Sahu (Michigan State University, United States)

LinkedIn: Priya Sahu

Abstract: Lignin is a major structural component of plant secondary cell walls and a key determinant of biomass utilization. In grasses, both phenylalanine and tyrosine contribute to lignin biosynthesis, but their respective roles in shaping the native lignin polymer have remained unclear. Here, we combine precursor-specific 13C isotope labeling with dynamic nuclear polarization (DNP)-enhanced solid-state NMR to directly track aromatic amino acid incorporation into lignin in intact Brachypodium distachyon cell walls. Conventional solid-state NMR established tissue-specific labeling patterns, while DNP provided up to ~40-fold sensitivity enhancement, enabling multidimensional 13C-13C correlation experiments on selectively labeled samples. We found that phenylalanine is the dominant precursor for canonical guaiacyl and syringyl lignin, whereas tyrosine preferentially contributes to hydroxyphenyl lignin and ferulate moieties characteristic of grass cell walls. Analysis of a C3H knockdown mutant further revealed precursor-dependent metabolic plasticity: phenylalanine-derived lignification was strongly impaired, while tyrosine-derived lignification remained comparatively resilient through alternative metabolic routing. These results demonstrate how DNP-enhanced solid-state NMR can directly connect precursor metabolism with polymer architecture in intact plant cell walls, providing new insights into the metabolic regulation of lignin biosynthesis in grasses.