Molecular mechanism of electrogenic carrier- and pump-mediated vacuolar transport

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The vacuolar membrane is engaged with solute transport into and out of the major plant organelle. Besides inorganic ions and metabolites, large quantities of protons and sugars are shuttled across this membrane. Two proton pumps, the V-ATPase and the VPPase, generate a proton- and electrical gradient across the vacuolar membrane that drives accumulation and release of sugars. Members of different gene families such as SUC, TMT, and VGT have been associated with a function in sugar transport and modulation of the vacuolar sugar pool. In the first funding period within the consortium we have studied the mode of action and properties of the V-type proton ATPase side by side with those of the sugar carriers SUC4 and TMT1/2. Using single vacuole-techniques combined with molecular approaches, transient overexpression, and electrophysiological analysis with Arabidopsis thaliana and mutants thereof we found that I. V-ATPase feeds back on pH gradient and membrane potential across the vacuolar membraneII. SUC4 operates as a H+/sucrose symporter for sugar release from the vacuoleIII. TMT1/2 represents the first proton-coupled sugar antiporter capable of high capacity glucose and sucrose loading into the vacuole.The central question regarding the 2nd term is how cold and salt alter the transport cycle of distinct vacuolar transporters. Given that the protein kinase VIK interacts with TMT1, in the following research period we will draw our attention on whether and how the TMT1- interacting kinase tunes the activity and selectivity of the sugar transporter. Following up with our proceeding studies on the V-ATPase, we will perform comparative studies regarding the second vacuolar proton pump, the pyrophosphatase (PPase). Furthermore we will draw our attention to ERD6, ERDL6, ERD3 and TLT1 as members of two subclades within the MST(- like) superfamily with a probable function in sugar transport.