The plant secondary cell wall is a complex structure composed of polysaccharides and lignin, and is a key evolutionary innovation of vascular land plants. Although cell wall composition is well understood, the cross-linking of the different polymers is only now yielding to investigation. Cross-linking between hemicelluloses and lignin occurs via two different mechanisms: incorporation into lignin by radical coupling of ferulate substitutions on xylan in commelinid monocots, and incorporation of hemicellulosic glycosyl residues by re-aromatisation of lignification intermediates. Recent genetic evidence indicates that hemicellulose:lignin cross-linking has a substantial impact on plant cell wall recalcitrance. Engineering plant biomass with modified frequencies of cross-links will have significant impacts on biomass utilisation.O.M.T was a recipient of an iCASE studentship from the BBSRC and Novozymes (Reference BB/M015432/1). P.D. was supported by the Leverhulme Trust Centre for Natural Material Innovation and the OpenPlant Synthetic Biology Research Centre BB/L014130/1
