Current cell-wall models assume no covalent bonding between cellulose and hemicelluloses such as xyloglu-can or mixed-linkageβ-D-glucan(MLG).However,Equisetum hetero-trans-β-glucanase(HTG)grafts cellu-lose onto xylo...Current cell-wall models assume no covalent bonding between cellulose and hemicelluloses such as xyloglu-can or mixed-linkageβ-D-glucan(MLG).However,Equisetum hetero-trans-β-glucanase(HTG)grafts cellu-lose onto xyloglucan oligosaccharides(XGOs)-and,we now show,xyloglucan polysaccharide-in vitro,thus exhibiting CXE(cellulose:xyloglucan endotransglucosylase)activity.In addition,HTG also catalyzes MLG-to-XGO bonding(MXE activity).In this study,we explored the CXE action of HTG in native plant cell walls and tested whether expansin exposes cellulose to HTG by disrupting hydrogen bonds.To quantify and visu-alize CXE and MXE action,we assayed the sequential release of HTG products from cell walls pre-labeled with substrate mimics.We demonstrated covalent cellulose--xyloglucan bonding in plant cell walls and showed that CXE and MXE action was up to 15%and 60%of total transglucanase action,respectively,and peaked in aging,strengthening tissues:CXE in xylem and cells bordering intercellular canals and MXE in scleren-chyma.Recombinant bacterial expansin(EXLX1)strongly augmented CXE activity in vitro.CXE and MXE ac-tion in living Equisetum structural tissues potentially strengthens stems,while expansin might augment the HTG-catalyzed CXE reaction,thereby allowing efficient CXE action in muro.Our methods will enable surveys for comparable reactions throughout the plant kingdom.Furthermore,engineering similar hetero-polymer formation into angiosperm crop plants may improve certain agronomic traits such as lodging tolerance.展开更多
基金We thank the UK Biotechnology and Biological Sciences Research Council(BBSRCBB/N002458/1)for fundingK.H.thanks the Villum Foundation(project TIPorNOT 00023089)for financial support during manuscript preparation.
文摘Current cell-wall models assume no covalent bonding between cellulose and hemicelluloses such as xyloglu-can or mixed-linkageβ-D-glucan(MLG).However,Equisetum hetero-trans-β-glucanase(HTG)grafts cellu-lose onto xyloglucan oligosaccharides(XGOs)-and,we now show,xyloglucan polysaccharide-in vitro,thus exhibiting CXE(cellulose:xyloglucan endotransglucosylase)activity.In addition,HTG also catalyzes MLG-to-XGO bonding(MXE activity).In this study,we explored the CXE action of HTG in native plant cell walls and tested whether expansin exposes cellulose to HTG by disrupting hydrogen bonds.To quantify and visu-alize CXE and MXE action,we assayed the sequential release of HTG products from cell walls pre-labeled with substrate mimics.We demonstrated covalent cellulose--xyloglucan bonding in plant cell walls and showed that CXE and MXE action was up to 15%and 60%of total transglucanase action,respectively,and peaked in aging,strengthening tissues:CXE in xylem and cells bordering intercellular canals and MXE in scleren-chyma.Recombinant bacterial expansin(EXLX1)strongly augmented CXE activity in vitro.CXE and MXE ac-tion in living Equisetum structural tissues potentially strengthens stems,while expansin might augment the HTG-catalyzed CXE reaction,thereby allowing efficient CXE action in muro.Our methods will enable surveys for comparable reactions throughout the plant kingdom.Furthermore,engineering similar hetero-polymer formation into angiosperm crop plants may improve certain agronomic traits such as lodging tolerance.
