Suppression of xylan endotransglycosylase PtxtXyn10A affects cellulose microfibril angle in secondary wall in aspen wood

Abstract

Certain xylanases from family GH10 are highly expressed during secondary wall deposition, but their function is unknown. We carried out functional analyses of the secondary-wall specific PtxtXyn10A in hybrid aspen (Populus tremula × tremuloides). PtxtXyn10A function was analysed by expression studies, overexpression in Arabidopsis protoplasts and by downregulation in aspen. PtxtXyn10A overexpression in Arabidopsis protoplasts resulted in increased xylan endotransglycosylation rather than hydrolysis. In aspen, the enzyme was found to be proteolytically processed to a 68 kDa peptide and residing in cell walls. Its downregulation resulted in a corresponding decrease in xylan endotransglycosylase activity and no change in xylanase activity. This did not alter xylan molecular weight or its branching pattern but affected the cellulose-microfibril angle in wood fibres, increased primary growth (stem elongation, leaf formation and enlargement) and reduced the tendency to form tension wood. Transcriptomes of transgenic plants showed downregulation of tension wood related genes and changes in stress-responsive genes. The data indicate that PtxtXyn10A acts as a xylan endotransglycosylase and its main function is to release tensional stresses arising during secondary wall deposition. Furthermore, they suggest that regulation of stresses in secondary walls plays a vital role in plant development.

Evolution of Xylan Substitution Patterns in Gymnosperms and Angiosperms: Implications for Xylan Interaction with Cellulose

“…S6). Therefore, the Magnoliales have a xylan decoration pattern very similar to eudicots (Bromley et al, 2013;Derba-Maceluch et al, 2015).…”

Evolution of the cell wall components during terrestrialization

“…Endo-β-1,4-xylanases probably are involved in the modification of the xylan in primary and secondary cell walls. Their exact function had not been explained yet, although recent studies have shown that in the secondary wood they are likely to be responsible for the releases tension in the secondary cell walls [95]. Because xylan endotransglycosylation activity is a relatively recent discovery, currently little is known about its emergence in the evolutionary aspect.…”

“…Phylogenetic analyzes have shown that both Selaginella and Physcomitrella have orthologs of IRX10, as well as IRX14/IRX14L and IRX9L, suggesting that the mechanism of 1,4-ß-D-xylan biosynthesis could be conserved in evolution. Interestingly, Ostreococcus (the smallest known eukaryote) contains several genes of GT43 families, which are known as those involved in the synthesis of 1,4-ß-D-xylan [91,94,95]. It is therefore possible, that the process of 1,4-ß-D-xylan biosynthesis preceded the evolution of land plant lineage [22].…”

“…The xylan endotransglycosylation activity was found in both, the primary cell walls of the many seeds plants and representatives of basal land plants [39], as well as in the secondary walls of poplar [95]. Endo-β-1,4-xylanases probably are involved in the modification of the xylan in primary and secondary cell walls.…”

Advances in Genetic Manipulation of Lignocellulose to Reduce Biomass Recalcitrance and Enhance Biofuel Production in Bioenergy Crops

“…Lately, in many genetic mutants and transgenic plants (rice, poplar, maize, and wheat) involved to hemicellulose biosynthesis have presented low biomass yield and high biomass digestibility [85][86][87][88]. Among the recognized mutants, GT43 and GT47 synthesize the backbone [89,90], while GT8 catalyze the addition of glucuronic acid residues and GT61 family have been recommended as candidates performing arabino furanose residue addition [91,92]. Currently, Xylan bioengineering is an important subject of research, because its presence in plant lignocellulosic biomass forcefully impacts the overall efficiency of enzymatic hydrolysis.…”