Biochemical and Functional Characterization of GALT8, an Arabidopsis GT31 β-(1,3)-Galactosyltransferase That Influences Seedling Development
journal contributionposted on 01.07.2021, 05:10 by JO Narciso, W Zeng, K Ford, ER Lampugnani, John HumphriesJohn Humphries, I Austarheim, A van de Meene, Tony BacicTony Bacic, Monika DoblinMonika Doblin
Arabinogalactan-proteins (AGPs) are members of the hydroxyproline-rich glycoprotein (HRGP) superfamily, a group of highly diverse proteoglycans that are present in the cell wall, plasma membrane as well as secretions of almost all plants, with important roles in many developmental processes. The role of GALT8 (At1g22015), a Glycosyltransferase-31 (GT31) family member of the Carbohydrate-Active Enzyme database (CAZy), was examined by biochemical characterization and phenotypic analysis of a galt8 mutant line. To characterize its catalytic function, GALT8 was heterologously expressed in tobacco leaves and its enzymatic activity tested. GALT8 was shown to be a β-(1,3)-galactosyltransferase (GalT) that catalyzes the synthesis of a β-(1,3)-galactan, similar to the in vitro activity of KNS4/UPEX1 (At1g33430), a homologous GT31 member previously shown to have this activity. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) confirmed the products were of 2-6 degree of polymerisation (DP). Previous reporter studies showed that GALT8 is expressed in the central and synergid cells, from whence the micropylar endosperm originates after the fertilization of the central cell of the ovule. Homozygous mutants have multiple seedling phenotypes including significantly shorter hypocotyls and smaller leaf area compared to wild type (WT) that are attributable to defects in female gametophyte and/or endosperm development. KNS4/UPEX1 was shown to partially complement the galt8 mutant phenotypes in genetic complementation assays suggesting a similar but not identical role compared to GALT8 in β-(1,3)-galactan biosynthesis. Taken together, these data add further evidence of the important roles GT31 β-(1,3)-GalTs play in elaborating type II AGs that decorate AGPs and pectins, thereby imparting functional consequences on plant growth and development.
WZ, EL, KF, JH, AvdM, MD, and AB acknowledge the support of a grant from the Australia Research Council (ARC) to the ARC Centre of Excellence in Plant Cell Walls [CE1101007]. WZ, MD, and AB acknowledge the support from the Overseas Expertise Introduction Project for Discipline Innovation "111" project (D18008). JON acknowledges the support of the University of Melbourne MRS and MIFRS scholarships. EL and JH acknowledge funding from the University of Melbourne, Faculty of Science.
JournalFrontiers in Plant Science
Article NumberARTN 678564
PublisherFRONTIERS MEDIA SA
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Science & TechnologyLife Sciences & BiomedicinePlant Sciencesplant cell wallseedling developmentgalactosyltransferasearabinogalactan-proteinsArabidopsis thalianaGALT8KNS4UPEX1ARABINOGALACTAN-PROTEINII ARABINOGALACTANCARBOHYDRATE MOIETIESCELLIDENTIFICATIONBIOSYNTHESISGLYCOSYLTRANSFERASEMOTIFSPROTEOGLYCANSCOMPONENTSKNS4/UPEX1