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. Preferentially expressed in roots. Restricted expression to the primary root in young seedlings. Later detected in hypocotyl, leaves but with the strongest expression in the root system. No visible phenotype. Displays smaller nematode-induced syncytia. The UGD2 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 mutants display abnormal nematode-induced syncytia (PubMed:22848518). Belongs to the UDP-glucose/GDP-mannose dehydrogenase family.