A study of the vesicle trafficking pathways regulating polar auxin transport and root development

PIN proteins have a crucial role in the polar transport of the phytohormone auxin in plant tissues. In some cell types, PIN proteins have a polar distribution at the plasma membrane. Vesicle trafficking is essential to generate this polarity but also for the control of the abundance of PIN proteins at the plasma membrane trough their internalisation and secretion. Among the molecular regulators of PIN trafficking, VAMP714, a SNARE protein responsible for vesicle fusion, was shown to be essential for PIN polarity. The aim was to investigate this molecular mechanism in more detail. A protein-protein interaction approach has allowed the identification of PIN trafficking regulators interacting with VAMP714 in intracellular compartments, possibly acting as recycling "hubs" for PIN proteins. Transcriptomic analysis of vamp714 mutants showed a reduced expression of a broad range of cell wall related genes. Consistently, cell wall composition is altered in those mutants. Confocal images showed that VAMP714 is required for the proper localization of cellulose synthase machinery. Also, the consequences of the changes in cell wall on PIN mobility at the plasma membrane were investigated. VAMP714 belongs to a family of four members, the VAMP71s. Unlike other VAMP71s that are tonoplast residents, VAMP714 mainly localizes to the Golgi. Comparisons of VAMP71 domains showed that only a small number of residues are responsible for the subcellular localization of VAMP714. In tissues and organs, different yet partly overlapping VAMP71 expression patterns were observed. The function of VAMP71s were also investigated and together with expression results indicate some level of sub-functionalization of VAMP71s.