Molecular and physiological characterization of vacuolar disaccharide and polyol transporters and of vacuolar monosaccharide transporter-like proteins
Final Report Abstract
In our project ‘Molecular and physiological characterization of vacuolar disaccharide and polyol transporters and of vacuolar monosaccharide transporter-like proteins’ we focused on sorting of the inositol transporter INT1, sorting and characterization of the sucrose transporter SUC4 and the elucidation of the physiological role of the putative monosaccharide transporters ERD6, ERDL3 and TLT1 from Arabidopsis thaliana. We identified a dileucine motif responsible for targeting of INT1 to the vacuolar membrane. In addition we could show that structural components defined by the N- terminus and enlarged middle loop are responsible for AP-3 dependent sorting of SUC4 to the tonoplast. We could show that SUC4 from Arabidopsis acts as H+/sucrose symporter, releasing sucrose from the vacuole. Furthermore we proved that also SUC4-type proteins from other plant species generally localize to the tonoplast. Our research on INT1, SUC4 and AP complex mediated sorting processes revealed that at least two independent sorting pathways from the Golgi apparatus to the tonoplast exist and that a back-up route for AP-3 cargos via other sorting complexes is likely. These results offer interesting aspects which will lead to further research on sorting processes within the plant cell. During further studies on ap-3 and ap-4 mutants we could identify the metal ion transporter NRAMP4 as a cargo of AP-4 and are currently studying further candidates assumed to be sorted by AP-3 and AP-4. The characterization of ERD6, ERDL3 and TLT1 included the detailed analysis promoter-GUS/GFP plants and overexpressing as well as knockout plants to elucidate the physiological role of these tonoplastic transport proteins. Additionally, we aimed to characterize the functional role of ERD6, ERDL3 and TLT1. Although numerous approaches were performed to identify the substrate of ERD6, ERDL3 and TLT1, the transported sugar(s) of these tonoplastic transporters could not be determined.
Publications
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(2011) Proton-driven sucrose symport and antiport are provided by the vacuolar transporters SUC4 and TMT1/2. Plant J. 68: 129-136
Schulz, A., Beyhl, D., Marten, I., Wormit, A., Neuhaus, H.E., Poschet, G., Büttner, M., Schneider, S., Sauer, N. and Hedrich, R.
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(2012) Routes to the tonoplast: The sorting of tonoplast transporters in Arabidopsis mesophyll protoplasts. Plant Cell 24: 215-232
Wolfenstetter, S., Wirsching, P., Dotzauer, D., Schneider, S. and Sauer, N.
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(2012) Vacuoles release sucrose via tonoplast-localised SUC4-type transporters. Plant Biol. 14: 325-336
Schneider, S., Hulpke, S., Schulz, A., Yaron, I., Höll, J., Imlau, A., Schmitt, B., Batz, S., Wolf, S., Hedrich, R. and Sauer, N.
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(2013) The endoplasmic reticulum is the main membrane source for biogenesis of the lytic vacuole in Arabidopsis. The Plant Cell 25: 3434-3449
Viotti, C., Krüger, F., Krebs, M., Neubert, C., Fink, F., Lupanga, U., Boutté, Y., Scheuring, D., Frescatada-Rosa, M., Wolfenstetter, S., Sauer, N., Hillmer, S., Grebe, M. and Schumacher, K.
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(2015) Sugar transport across the plant vacuolar membrane: nature and regulation of carrier proteins. Curr. Opin. Plant Biol. 25: 63-70
Hedrich, R., Sauer, N. and Neuhaus, H.E.
