Galactoglucomannan structure of Arabidopsis seed‐coat mucilage in GDP‐mannose synthesis impaired mutants

Abstract

Cell-wall polysaccharides are synthesized from nucleotide sugars by glycosyltransferases.However, in what way the level of nucleotide sugars affects the structure of the polysaccharides is not entirely clear. guanosine diphosphate (GDP)-mannose (GDP-Man) is one of the major nucleotide sugars in plants and serves as a substrate in the synthesis of mannan polysaccharides. GDP-Man is synthesized from mannose 1-phosphate and GTP by a GDP-Man pyrophosphorylase, VITAMIN C DEFECTIVE1 (VTC1), which is positively regulated by the interacting protein KONJAC1 (KJC1) in Arabidopsis. Since seed-coat mucilage can serve as a model of the plant cell wall, we examined the influence of vtc1 and kjc1 mutations on the synthesis of mucilage galactoglucomannan. Sugar composition analysis showed that mannose content in adherent mucilage of kjc1 and vtc1 mutants was only 42% and 11% of the wild-type, respectively, indicating a drastic decrease of galactoglucomannan. On the other hand, structural analysis based on specific oligosaccharides released by endo-β-1,4-mannanase indicated that galactoglucomannan had a patterned glucomannan backbone consisting of alternating residues of glucose and mannose and the frequency of α-galactosyl branches was also similar to the wild type structure. These results suggest that the structure of mucilage galactoglucomannan is mainly determined by properties of glycosyltransferases rather than the availability of nucleotide sugars. | INTRODUCTIONMucilage extruded from the seed-coat epidermis is a gelatinous compound that helps seeds to germinate. In Arabidopsis, pectin RG-I and homogalacturonan account for most seed-coat mucilage (Naran et al., 2008), but other polysaccharides, including cellulose and galactoglucomannan, also play important roles in the conformation of mucilage and adhesion to the seed (Griffiths

Genome-wide identification and expression analysis of GDP-D-mannose pyrophosphorylase and KATANIN in Corymbia citriodora

“…Its paralogous gene, At1G74910.2 (KJC1), is homologous to human GMPPA (GMP alpha subunits) and likely interacts with AtCYT1 protein to positively regulate GMP activity, thereby promoting the synthesis of GDP-D-mannose (Zheng et al, 2021). Among them, the mannose content of vct1-1 was significantly lower than that of kjc mutant (Sawake et al, 2015;Nishigaki et al, 2021), indicating that CcGMP7 and CcGMP4 had a mutually reinforcing effect, and CcGMP4 regulated mannosesynthesis in a large proportion. The GO annotation results for CcGMP7 and CcGMP4 differed in that the former lacked binding activity with organic and heterocyclic compounds, which may account for its lower expression level compared to the latter.…”

Modern mannan: a hemicellulose's journey

“…VITAMIN C DEFECTIVE1 (VTC1; also known as GMP1/CYT1) is the major PPase producing GDP‐Man in Arabidopsis (Table 1) and its activity is enhanced via physical interactions with the KONJAC1 (KJC1) and KJC2 protein co‐factors (Sawake et al ., 2015). Genetically reducing GDP‐Man availability in vtc1 and kjc1 mutant seeds severely reduced GGM content in Arabidopsis mucilage (Nishigaki et al ., 2021). However, the kjc1 mucilage displayed a surprisingly normal gel electrophoresis profile of GGM oligosaccharides (Fig.…”

Crystal Structures of Arabidopsis thaliana GDP-D-Mannose Pyrophosphorylase VITAMIN C DEFECTIVE 1

“…The first plant GMPase gene VITAMIN C DEFECTIVE 1 ( VTC1 ) was genetically defined in the model plant Arabidopsis thaliana (Arabidopsis) by screening the vitamin C-deficient mutants ( Conklin et al, 1997 , 1999 ), and was found to be identical to the gene CYTOKINESIS DEFECTIVE1 ( Lukowitz et al, 2001 ). Studies of the Arabidopsis vtc1 mutants have revealed that VTC1 is implicated in physiological processes including cell-wall formation ( Nickle and Meinke, 1998 ; Nishigaki et al, 2021 ), cytokinesis ( Falbel et al, 2003 ), control of the transcription of defense-related and senescence-associated genes ( Pastori et al, 2003 ; Barth et al, 2004 ; Pavet et al, 2005 ), and ammonium sensitivity ( Qin et al, 2008 ; Barth et al, 2010 ). These findings reflect the diverse functions of the nucleotide sugar GDP-Man in plants ( Bar-Peled and O’Neill, 2011 ; Figueroa et al, 2021 ).…”