Abstract
Arabinogalactan proteins (AGPs) contain arabinogalactan (AG) polysaccharides that are biologically relevant to plant growth processes. Here, the biochemical and physiological roles of three Golgi localized β-glucuronosyltransferase genes (GLCAT14A, GLCAT14B and GLCAT14C) in Arabidopsis thaliana, responsible for the addition of glucuronic acid to AG chains, were further investigated using single, double and triple glcat14 mutant plants. These proteins were localized to the Golgi apparatus when transiently expressed in Nicotiana benthamiana. Sugar analysis of AGP extracts from Arabidopsis stem, leaf and siliques showed a consistent reduction in glucuronic acid in glcat14 mutants relative to wild type, with concomitant effects resulting in tissue-specific alterations, especially in arabinose and galactose sugars. Although we observed defects in trichome branching in glca14a/b and glca14a/b/c mutants, scanning electron microscope analysis/energy dispersive microanalysis (SEM/EDX) showed no difference in the calcium content of trichomes in these mutants relative to wild type. Immunoblot analyses of the stem and leaf showed a reduction in AGPs as detected with the LM2 antibody in glcat14a/b and glcat14a/b/c mutants relative to wild type. The current work exemplifies the possibility of conducting structure-function assessment of cell wall biosynthetic genes to identify their physiological roles in plant growth and development.
Highlights
Accepted: 1 June 2021Plant cell walls are composed of structurally complex heteropolymers that are essential to plant development
Using scanning electron micrography (SEM), we examined the trichome defects of study found that trichome defects in glcat14 mutants were suppressed in a
Previous work identified eleven glucuronic acid transferases (GLCATs) genes in Arabidopsis that belong to the carbohydrate active enzyme (CAZy) GT14 family [17,28]; these genes may be involved in the glucuronidation of Type II AGs, given their conserved genetic architecture and the conserved GLCAT domain present in genes [17]
Summary
Plant cell walls are composed of structurally complex heteropolymers that are essential to plant development. Arabinogalactan-proteins (AGPs) are a family of complex proteoglycans found in the plant cell walls of all higher plants [1] and contain a large amount of arabinogalactan polysaccharide (90% w/w) attached to hydroxyproline residues in their protein cores [2]. AGPs belong to a superfamily of structural macromolecules known as the hydroxyproline-rich glycoproteins (HRGPs), of which extensins and proline-rich proteins are members with unique carbohydrate moieties central to their biological functions [3]. AGPs have N-terminal signal peptides, which are cleaved to allow for secretion, and about half of AGP family members have C-terminal glycosylphosphatidylinositol (GPI) anchors to allow for their retention and attachment to the outer leaflet of the plasma membrane [5].
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