Topological organization of UDP-arabinose metabolism controls arabinose incorporation into Arabidopsis cell wall polysaccharides
Ariel Orellana (Chile)1 2; Ricardo Yusta (Chile)1 2; Asier Largo-Gosens (Spain)3 4; Juan P. Parra-Rojas (Chile)1; Dayan Sanhueza (Chile)1; Rachel A. Mertz (United States)5; Christopher K. Dugard (United States)5; Carsten Rautengarten (Germany)6; Alvaro Miquel (Chile)1 2; Berit Ebert (Germany)6; Susana Sáez-Aguayo (Chile)1 2;
1 - Universidad Andrés Bello; 2 - Center for Advancing Agri-Food System Transformation; 3 - Área de Fisiología Vegetal, Departamento de Ingeniería y Ciencias Agrarias, Universidad de León, León, Spain; 4 - Instituto de Biología Molecular, Genómica y Proteómica (INBIOMIC), Universidad de León, León, Spain; 5 - Department of Botany & Plant Pathology, 915 Mitch Daniels Blvd., Purdue University, West Lafayette, IN 47907; 6 - Ruhr-University Bochum;
Keywords: Nucleotide sugar transporters; Topology of Arabinosylation; UDP-arabinose;
Abstract Topics: Theme 1: Pectins: Structure, Remodeling, and Function
Type of Presentation: Oral Communication

Abstract text: Arabinose incorporation into plant cell wall polysaccharides depends on the coordinated synthesis, transport, and utilization of UDP-arabinopyranose (UDP-Arap) and UDP-arabinofuranose (UDP-Araf). A central topological challenge in this pathway is that UDP-Arap can be generated in the Golgi lumen, whereas UDP-Araf is produced by cytosolic UDP-arabinopyranose mutase (UAM) and must then be re-imported into the Golgi for arabinosylation. To test the functional importance of this compartmentation, we combined genetic, cell biological, and biochemical approaches in Arabidopsis. Golgi-luminal retargeting of UAM1 reduced total cell wall arabinose, selectively depleted Araf linkages while largely preserving Arap, and enhanced salt-sensitive root swelling and growth inhibition in uam1 backgrounds, indicating that productive arabinosylation requires spatial separation of UDP-Arap production and UDP-Araf formation. We further identified UAPT1/At1g77610 as a Golgi-localized UDP-Arap transporter candidate. UAPT1-mediated transport was strongest in exchange with UDP-GlcA, was saturable, and also supported UDP-Arap exchange with UDP-Gal, but not detectable UDP-Araf transport. Three independent uapt1 alleles showed reduced mucilage area and decreased Ara, Gal, and GlcA, together with lower Ara and Gal in mucilage RG-I and RG-II. Together, these results indicate that Golgi topology is essential for sustaining the metabolic flux that underpins arabinose incorporation into cell wall polysaccharides.