Involved in the biosynthesis of UDP-glucuronic acid (UDP-GlcA), providing nucleotide sugars for cell-wall polymers. Required for the formation of cell wall ingrowths on the outer cell walls of nematode-induced syncytia. H2O + 2 NAD(+) + UDP-alpha-D-glucose = 3 H(+) + 2 NADH + UDP-alpha-D-glucuronate Inhibited by UDP-xylose. Nucleotide-sugar biosynthesis; UDP-alpha-D-glucuronate biosynthesis; UDP-alpha-D-glucuronate from UDP-alpha-D-glucose: step 1/1. Restricted expression to the primary root in young seedlings. Later detected in hypocotyl, leaves and flowers. No visible phenotype. Displays smaller nematode-induced syncytia. Ugd2 and ugd3 double mutant displays a strong dwarf phenotype and often develops seedlings with severe root defects; cell walls have an altered sugar composition (PubMed:21949134). Ugd2 and ugd3 double mutant displays abnormal nematode-induced syncytia (PubMed:22848518). Belongs to the UDP-glucose/GDP-mannose dehydrogenase family.