A β-glucuronosyltransferase from Arabidopsis thaliana involved in biosynthesis of type II arabinogalactan has a role in cell elongation during seedling growth.
We have characterized a β-glucuronosyltransferase (AtGlcAT14A) from Arabidopsis thaliana that is involved in the biosynthesis of type II arabinogalactan (AG). This enzyme belongs to the Carbohydrate Active Enzyme database glycosyltransferase family 14 (GT14). The protein was localized to the Golgi apparatus when transiently expressed in Nicotiana benthamiana. The soluble catalytic domain expressed in Pichia pastoris transferred glucuronic acid (GlcA) to β-1,6-galactooligosaccharides with degrees of polymerization (DP) ranging from 3-11, and to β-1,3-galactooligosaccharides of DP5 and 7, indicating that the enzyme is a glucuronosyltransferase that modifies both the β-1,6- and β-1,3-galactan present in type II AG. Two allelic T-DNA insertion mutant lines showed 20-35% enhanced cell elongation during seedling growth compared to wild-type. Analyses of AG isolated from the mutants revealed a reduction of GlcA substitution on Gal-β-1,6-Gal and β-1,3-Gal, indicating an in vivo role of AtGlcAT14A in synthesis of those structures in type II AG. Moreover, a relative increase in the levels of 3-, 6- and 3,6-linked galactose (Gal) and reduced levels of 3-, 2- and 2,5-linked arabinose (Ara) were seen, suggesting that the mutation in AtGlcAT14A results in a relative increase of the longer and branched β-1,3- and β-1,6-galactans. This increase of galactosylation in the mutants is most likely caused by increased availability of the O6 position of Gal, which is a shared acceptor site for AtGlcAT14A and galactosyltransferases in synthesis of type II AG, and thus addition of GlcA may terminate Gal chain extension. We discuss a role for the glucuronosyltransferase in the biosynthesis of type II AG, with a biological role during seedling growth.
['Knoch|Eva|E|', 'Dilokpimol|Adiphol|A|', 'Tryfona|Theodora|T|', 'Poulsen|Christian P|CP|', 'Xiong|Guangyan|G|', 'Harholt|Jesper|J|', 'Petersen|Bent L|BL|', 'Ulvskov|Peter|P|', 'Hadi|Masood Z|MZ|', 'Kotake|Toshihisa|T|', 'Tsumuraya|Yoichi|Y|', 'Pauly|Markus|M|', 'Dupree|Paul|P|', 'Geshi|Naomi|N|']
D017360:Arabidopsis D029681:Arabidopsis Proteins D001089:Arabinose D001692:Biological Transport D020134:Catalytic Domain D002473:Cell Wall D005685:Galactans D015870:Gene Expression D014453:Glucuronosyltransferase D006056:Golgi Apparatus D008961:Models, Structural D016254:Mutagenesis, Insertional D010641:Phenotype D010802:Phylogeny D010843:Pichia D011994:Recombinant Proteins D036226:Seedlings D013379:Substrate Specificity D014026:Tobacco
Arabidopsis thaliana type II arabinogalactan glycosyltransferase family 14 Golgi apparatus glucuronosyltransferase arabinogalactan protein plant cell wall