Evolution of glucuronoxylan side chain variability in vascular plants and the compensatory adaptations of cell wall-degrading hydrolases.

Polysaccharide structural complexity not only influences cell wall strength and extensibility but also hinders pathogenic and biotechnological attempts to saccharify the wall. In certain species and tissues, glucuronic acid side groups on xylan exhibit arabinopyranose or galactose decorations whose genetic and evolutionary basis is completely unknown, impeding efforts to understand their function and engineer wall digestibility. Genetics and polysaccharide profiling were used to identify the responsible loci in Arabidopsis and Eucalyptus from proposed candidates, while phylogenies uncovered a shared evolutionary origin. GH30-family endo-glucuronoxylanase activities were analysed by electrophoresis, and their differing specificities were rationalised by phylogeny and structural analysis. The newly identified xylan arabinopyranosyltransferases comprise an overlooked subfamily in the GT47-A family of Golgi glycosyltransferases, previously assumed to comprise mainly xyloglucan galactosyltransferases, highlighting an unanticipated adaptation of both donor and acceptor specificities. Further neofunctionalisation has produced a Myrtaceae-specific xylan galactosyltransferase. Simultaneously, GH30 endo-glucuronoxylanases have convergently adapted to overcome these decorations, suggesting a role for these structures in defence. The differential expression of glucuronoxylan-modifying genes across Eucalyptus tissues, however, hints at further functions. Our results demonstrate the rapid adaptability of biosynthetic and degradative carbohydrate-active enzyme activities, providing insight into plant-pathogen interactions and facilitating plant cell wall biotechnological utilisation.This work was supported by the Leverhulme Trust Centre for Natural Material Innovation, the Biotechnology and Biological Sciences Research Council (BBSRC) of the UK as part of the OpenPlant Synthetic Biology Research Centre (Reference BB/L014130/1), The UKRI grant underwriting the ERC advanced grant (EVOCATE Function and evolution of plant cell wall architecture for sustainable technologies. EP/X027120/1), Innovate UK, the Cambridge BBSRC-DTP Programme (Reference BB/J014540/1), a Novo Nordisk Foundation grant Oxymist (Grant Number NNF20OC0059697), and a BBSRC iCASE studentship (Reference 648 BB/M015432/1)

Evolution of glucuronoxylan side chain variability in vascular plants and the compensatory adaptations of cell wall–degrading hydrolases

Publication status: PublishedSummary Polysaccharide structural complexity not only influences cell wall strength and extensibility but also hinders pathogenic and biotechnological attempts to saccharify the wall. In certain species and tissues, glucuronic acid side groups on xylan exhibit arabinopyranose or galactose decorations whose genetic and evolutionary basis is completely unknown, impeding efforts to understand their function and engineer wall digestibility. Genetics and polysaccharide profiling were used to identify the responsible loci in Arabidopsis and Eucalyptus from proposed candidates, while phylogenies uncovered a shared evolutionary origin. GH30‐family endo‐glucuronoxylanase activities were analysed by electrophoresis, and their differing specificities were rationalised by phylogeny and structural analysis. The newly identified xylan arabinopyranosyltransferases comprise an overlooked subfamily in the GT47‐A family of Golgi glycosyltransferases, previously assumed to comprise mainly xyloglucan galactosyltransferases, highlighting an unanticipated adaptation of both donor and acceptor specificities. Further neofunctionalisation has produced a Myrtaceae‐specific xylan galactosyltransferase. Simultaneously, GH30 endo‐glucuronoxylanases have convergently adapted to overcome these decorations, suggesting a role for these structures in defence. The differential expression of glucuronoxylan‐modifying genes across Eucalyptus tissues, however, hints at further functions. Our results demonstrate the rapid adaptability of biosynthetic and degradative carbohydrate‐active enzyme activities, providing insight into plant–pathogen interactions and facilitating plant cell wall biotechnological utilisation. </jats:p