KONJAC1 and 2 Are Key Factors for GDP-Mannose Generation and Affect l-Ascorbic Acid and Glucomannan Biosynthesis in Arabidopsis |
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Authors: | Shota Sawake Noriaki Tajima Jenny C Mortimer Jeemeng Lao Toshiki Ishikawa Xiaolan Yu Yukiko Yamanashi Yoshihisa Yoshimi Maki Kawai-Yamada Paul Dupree Yoichi Tsumuraya Toshihisa Kotake |
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Institution: | aGraduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan ;bDepartment of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom;cBiomass Engineering Program Cooperation Division, RIKEN Center for Sustainable Resource Science, Yokohama 230-0045, Japan ;dJoint Bioenergy Institute, Emeryville, California 94608 |
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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. |
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