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

Abstract

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.