KONJAC1 and 2 Are Key Factors for GDP-Mannose Generation and Affect l-Ascorbic Acid and Glucomannan Biosynthesis in Arabidopsis

摘要

Humans are unable to synthesize l-ascorbic acid (), yet it is required as a cofactor in many critical biochemical reactions. The majority of human dietary is obtained from plants. In Arabidopsis thaliana, a GDP-mannose pyrophosphorylase (), VITAMIN C DEFECTIVE1 (VTC1), catalyzes a rate-limiting step in 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 activity to 10% of wild-type levels, leading to a 60% reduction in levels. On the contrary, overexpression of KJC1 significantly increased 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 activity of recombinant VTC1 in vitro, while KJCs did not show activity. Yeast two-hybrid assays suggested that the stimulation of activity occurs via interaction of KJCs with VTC1. These results suggest that KJCs are key factors for the generation of GDP-Man and affect level and glucomannan accumulation through the stimulation of VTC1 activity.