Associate Professor University of Missouri-Columbia Columbia, Missouri
Body of Abstract: In Arabidopsis thaliana, the hormone auxin drives plant growth by mediating cell division and cell expansion. For proper root growth and development, internal levels of auxin and its storage form, indole-3-butyric acid (IBA), must be tightly regulated. To maintain appropriate intracellular levels of IBA in roots, plants rely on IBA efflux transporters that need to be at their correct abundance and subcellular location, namely the outer plasma membrane (PM) domain of root epidermal cells. Vesicular trafficking, which is the movement of cargo proteins from one organelle to is implicated in governing correct PM localization of IBA efflux transporters. So far, however, very little is known about the identity and roles of vesicle components with roles in trafficking IBA efflux transporters to the PM, except that these components apparently differ to those required for PM-localization of PIN-FORMED (PIN) protein family of auxin transporters.
Clathrin-coated vesicles are the best studied vesicles that form at the PM and the trans-Golgi Network (TGN) to modulate the PM proteome. EPSIN1 is a TGN-localized clathrin adaptor protein that we have shown to modulate the PM abundance of immune (co-)receptors for effective plant defense responses. Here, we used large-scale quantitative proteomics of enriched PM to identify a novel role for the vesicular trafficking protein EPSIN1 (EPS1) in regulating the PM abundance of the IBA efflux transporter PLEIOTROPIC DRUG RESISTANCE9 / ATP BINDING CASSETTE G37 (PDR9/ABCG37). Using a combination of biochemical PM enrichment and live-cell imaging, we provide evidence that loss of EPS1 resulted in reduced PM abundance of PDR9 in roots, which correlated with IBA response and growth defects reminiscent of those observed in pdr9-2 null mutants. Thus, our work expands the limited knowledge of vesicular trafficking components that help regulate the correct accumulation of IBA transporters at the PM to ensure proper plant growth and development.