Modifying Sugar Content in Plant Vacuoles

Ekkehard Neuhaus - Michael Schroda - Patrick Lang/Jan Hauth

The modulation of both, the total amount and partitioning of cellular sugars is a key mechanism how plants achieve optimal development, maximal yield and tolerance against biotic and abiotic stress stimuli. Sugars accumulate in the large central vacuole, especially in photosynthesizing mesophyll cells and in vacuoles from storage organs, e.g. sugar-beet tap roots. Corresponding changes of sugar compartmentalization in cells have to be tightly regulated since rates of photosynthesis, vacuolar sugar import and export, respiratory activity and sugar export to other organs must be balanced to adapt to environmental conditions and developmental stages.

Given the large volume of the mesophyll vacuole and given the strong feed-back action of cytosolic sugar concentrations on chloroplast function (here mainly photosynthetic efficiency) great attention has to be paid to transport processes across the vacuolar membrane. For this, we will decipher how known vacuolar sugar importers and exporters are regulated on the genetic and post-translational level, we will analyze how corresponding protein kinases, protein phosphatases and putative receptor kinases are involved in the regulation of tonoplast transport proteins and finally, we aim to identify novel, so far non-discovered vacuolar carrier proteins involved in cellular sugar homeostasis. We aim to quantify the amounts of corresponding proteins in vacuolar membranes, we will elucidate the phosphorylation state of transporters and corresponding effector proteins (e.g. protein kinases) and we develop tools to determine cellular and sub-cellular metabolites pools. All of these approaches depend upon the intensive use of mass-spectrometry. On the long run we hope to correlate metabolic fluxes and changes in sugar concentrations with the presence of transporters and their respective activation state. A transfer to crop species seems feasible.