Two conifer GUX clades are responsible for distinct glucuronic acid patterns on xylan

Wood of coniferous trees (softwood), is a globally significant carbon sink and an important source biomass. Despite that, little known about the genetic basis softwood cell wall biosynthesis. Branching xylan, one main hemicelluloses in secondary walls, with glucuronic acid (GlcA) critical for biomass recalcitrance. Here, we investigate decoration patterns xylan by conifer GlucUronic substitution Xylan (GUX) enzymes. Through molecular phylogenetics identify two distinct GUX clades. Using transcriptional profiling show that genes are preferentially expressed forming tissues. With vitro planta assays demonstrate enzymes from both clades active glucuronyltransferases. Conifer each clade have different specific activities. While members add evenly spaced GlcA branches, also capable glucuronidating consecutive xyloses. Importantly, these types patterning present softwood. As might modulate xylan–cellulose xylan–lignin interactions, our results further understanding biosynthesis provide breeding or engineering targets can be used to modify properties.