The Mechanism by which Arabidopsis Vesicle Associated Membrane Proteins Regulate Root Development Under Salt Stress

Abstract

When plants are grown in saline soil, they deploy their vesicle trafficking system to alter membrane protein dynamics rapidly. High-salt conditions induce prompt ionic and osmotic stresses, subsequently leading to the generation of reactive oxygen species. In response to salt stress, roots, being the initial affected organs, experience inhibited growth, limiting water and nutrient absorption and, consequently, reducing overall plant biomass and crop yield. In eukaryotic cells, intracellular vesicle trafficking serves vital roles, including membrane trafficking and delivery of cargo proteins to their designated destinations. A major exocytic route in plants is vesicle trafficking to the cell plasma membrane and the vacuole, which plays an essential role in plant salt tolerance. The proposed role for a vesicle-mediated trafficking system which adjusts the localisation and availability of transporters of the plant hormone auxin to facilitate rapid changes in directional root growth was investigated; auxin is known to regulate root development under salt stress. Specifically, the focus of the work described is the family of VESICLE ASSOCIATED MEMBRANE PROTEIN 71 (VAMP71) R-SNAREs in Arabidopsis thaliana, which may play a role in auxin transporter function but whose precise role in root development under salt stress has not been explored before. This thesis presents transcriptomic and proteomic evidence that VAMP71 family members are important for the correct regulation of auxin transport and signalling events under salt stress. The results also indicate a high degree of redundancy between the VAMP71 genes. Quantitative proteomics identified putative VAMP712-dependent targets by analysing differentially expressed proteins between wild-type Arabidopsis and vamp712 loss-of-function mutants exposed to salt stress. Proteins associated with auxin homeostasis and other vesicle-mediated processes associated with the plant cell vacuole were identified by gene ontology analysis. Confocal microscopy also revealed that the loss of function of vamp712 and vamp713 disrupted the abundance and distribution of auxin transporters at the root tip. Overall, this study has strengthened the link between VAMP71 family genes and auxin-mediated processes and highlights the genotype-dependent sensitivity to salt stress and exogenous auxin.