Physiological and cellular effects of TENin1, a novel small molecule inhibitor of endomembrane protein trafficking

Gravitropic response is required for proper orientation of plant growth and development. One of the factors that influence gravitropism in plants is the polar distribution of the plant hormone auxin, which is maintained by auxin transporters at the plasma membrane (PM). These endomembrane proteins are transported to the PM via the secretory pathway and undergo constitutive endocytic recycling from the PM. This thesis characterises an inhibitor of endomembrane protein trafficking, Trafficking & ENdocytosis inhibitor 1 TENin1 (TE1), that reduces gravitropic response in Arabidopsis thaliana seedlings. Short term TE1 treatment causes intracellular accumulation of membrane proteins including brassinosteroid receptor BRI1, aquaporin PIP2a, and auxin transporters PIN2 and PIN7. All the accumulated experimental evidence gained throughout the duration of this project also suggest that TE1 interferes with the endomembrane recycling to the TGN both from the pre-vacuolar compartment (PVC) and the PM therefore causing accumulation of PIN2-GFP at the PVC, which is eventually re-directed to the vacuole. The long term effects of TE1 were also characterised and revealed dose-dependent growth inhibition of whole plants and reduction in organelle dynamics. In a separate study in the laboratory two Arabidopsis thaliana accessions that displayed resistance to the effects of TE1 were identified. A library of Arabidopsis thaliana recombinant inbred lines (RILs) generated by crossing a TE1 resistant accession with the sensitive Columbia accession was commercially available. Therefore, 174 and 117 RILs were screened for different traits to identify a region of the genome responsible for the resistance to the effects of TE1. The data generated from the RIL screens revealed a major resistant locus lies within 9 to 16 Mb in the chromosome 5. A further study is now required to map the target gene(s) responsible for the resistance to TE1.