Trifunctional enzyme involved in UDP-beta-L-rhamnose biosynthesis, a precursor of the primary cell wall components rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II) (PubMed:14671019, PubMed:17190829, PubMed:19056285). Plays a major role in supplying UDP-rhamnose for flavonol biosynthesis (PubMed:18757557). Catalyzes the dehydration of UDP-glucose to form UDP-4-dehydro-6-deoxy-D-glucose followed by the epimerization of the C3' and C5' positions of UDP-4-dehydro-6-deoxy-D-glucose to form UDP-4-keto-beta-L-rhamnose and the reduction of UDP-4-keto-beta-L-rhamnose to yield UDP-beta-L-rhamnose (By similarity). UDP-alpha-D-glucose = H2O + UDP-4-dehydro-6-deoxy-alpha-D-glucose Carbohydrate biosynthesis. Expressed in roots, stems, leaves, seedlings, inflorescence tips, and siliques. Detected in the adaxial side of cotyledons, in the emerging leaves and in trichomes. Also detected in the root tip, more precisely in the epidermal cells in the meristematic and elongation zone. The dehydratase activity is contained in the N-terminal region while the epimerase and reductase activities are in the C-terminal region. Hyponastic growth, aberrant pavement cell and stomatal morphology in cotyledons, and defective trichome formation. The increased accumulation of auxin in rol1-2 seedlings appears to be caused by a flavonol-induced modification of auxin transport (PubMed:18567791, PubMed:21502189). In bacteria, TDP-L-rhamnose is formed by the successive action of three different enzymes on TDP-D-glucose. In plants, on the other hand, a single polypeptide probably catalyzes all three reactions that lead to the conversion of UDP-D-glucose to UDP-L-rhamnose. In the N-terminal section; belongs to the NAD(P)-dependent epimerase/dehydratase family. dTDP-glucose dehydratase subfamily. In the C-terminal section; belongs to the dTDP-4-dehydrorhamnose reductase family.