ABSTRACT
Humans are unable to synthesize l-ascorbic acid (AsA), yet it is required as a cofactor in many critical biochemical reactions. The majority of human dietary AsA is obtained from plants. In Arabidopsis thaliana, a GDP-mannose pyrophosphorylase (GMPP), VITAMIN C DEFECTIVE1 (VTC1), catalyzes a rate-limiting step in AsA synthesis: the formation of GDP-Man. In this study, we identified two nucleotide sugar pyrophosphorylase-like proteins, KONJAC1 (KJC1) and KJC2, which stimulate the activity of VTC1. The kjc1kjc2 double mutant exhibited severe dwarfism, indicating that KJC proteins are important for growth and development. The kjc1 mutation reduced GMPP activity to 10% of wild-type levels, leading to a 60% reduction in AsA levels. On the contrary, overexpression of KJC1 significantly increased GMPP activity. The kjc1 and kjc1kjc2 mutants also exhibited significantly reduced levels of glucomannan, which is also synthesized from GDP-Man. Recombinant KJC1 and KJC2 enhanced the GMPP activity of recombinant VTC1 in vitro, while KJCs did not show GMPP activity. Yeast two-hybrid assays suggested that the stimulation of GMPP activity occurs via interaction of KJCs with VTC1. These results suggest that KJCs are key factors for the generation of GDP-Man and affect AsA level and glucomannan accumulation through the stimulation of VTC1 GMPP activity.
Subject(s)
Arabidopsis/genetics , Ascorbic Acid/metabolism , Guanosine Diphosphate Mannose/metabolism , Mannans/metabolism , Nucleotidyltransferases/metabolism , Vitamins/metabolism , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Cell Wall/metabolism , Gene Expression Regulation, Plant , Mutation , Nucleotidyltransferases/genetics , Phylogeny , Plant Roots/genetics , Plant Roots/metabolism , Plants, Genetically Modified , Seedlings/genetics , Seedlings/metabolismABSTRACT
The article "Metabolism of L-arabinose in plants", written by "Toshihisa Kotake, Yukiko Yamanashi, Chiemi Imaizumi, Yoichi Tsumuraya", was originally published Online First without open access. After publication in volume129, issue 5, page 781-792 the Botanical Society of Japan decided to opt for Open Choice and to make the article an open access publication.
ABSTRACT
L-Arabinose (L-Ara) is a plant-specific sugar accounting for 5-10 % of cell wall saccharides in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa). L-Ara occurs in pectic arabinan, rhamnogalacturonan II, arabinoxylan, arabinogalactan-protein (AGP), and extensin in the cell walls, as well as in glycosylated signaling peptides like CLAVATA3 and small glycoconjugates such as quercetin 3-O-arabinoside. This review focuses on recent advances towards understanding the generation of L-Ara and the metabolism of L-Ara-containing molecules in plants.