Cellulose is synthesized at the plasma membrane by cellulose synthase (CESA) complexes (CSCs), which are assembled in the Golgi and secreted to the plasma membrane through the trans-Golgi network (TGN) compartment. However, the molecular mechanisms that guide CSCs through the secretory system and deliver them to the plasma membrane are poorly understood. Here, we identified an uncharacterized gene, TRANVIA (TVA), that is transcriptionally coregulated with the CESA genes required for primary cell wall synthesis. The tva mutant exhibits enhanced sensitivity to cellulose synthesis inhibitors; reduced cellulose content; and defective dynamics, density, and secretion of CSCs to the plasma membrane as compared to wild type. TVA is a plant-specific protein of unknown function that is detected in at least two different intracellular compartments: organelles labeled by markers for the TGN and smaller compartments that deliver CSCs to the plasma membrane. Together, our data suggest that TVA promotes trafficking of CSCs to the plasma membrane by facilitating exit from the TGN and/or interaction of CSC secretory vesicles with the plasma membrane.
