Defining the role of the two vacuolar proton-pumps during stress responses

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Although it is generally assumed that the combined action of the vacuolar H+-ATPase (V-ATPase) and the vacuolar H+-pyrophosphatase (V-PPase) energizes transport across the tonoplast, their relative contribution to vacuolar and cytosolic pH-homeostasis during coldand osmotic stress has not been determined. During the first funding period, we have established that under non-stress conditions the V-PPase does not contribute to vacuolar acidification. Surprisingly, we found that in addition to the tonoplast V-ATPase, the endosomal VATPase seems to play an important role in vacuolar acidification and stress tolerance. Based on these results, focus will be on the function and regulation of the V-ATPase in the dynamic continuum of endomembrane compartments that ultimately delivers cargo to the central vacuole. In addition, we will continue our efforts to determine the role of the V-PPase under cold- and osmotic stress by using nanosensors for pH and key metabolites.