SFB 429 III: Interactions and regulation of sucrose transporter proteins from Solanum tuberosum (TP B 11)

Sucrose represents the major transport form for carbohydrates in plants. Three members of the sucrose transporter family with different properties were identified: SUT1, as a high affinity sucrose proton cotransporter, SUT4 as a low affinity transporter and SUT2, which in yeast is not functional and show features reminiscent of the yeast sugar sensors RGT2 and SNF3. In analogy to the yeast and human glucose sensors, SUT2 contains extended cytosolic domains, with highly conserved regions indicating that SUT2 might be involved in sucrose sensing. Immunolocalization demonstrates that all three SUT proteins are localized in the same enucleate sieve element and the potential of sucrose transporters to form homo-oligomers was demonstrated by help of the yeast-based split ubiquitin system. The results show that both SUT1 and SUT2 have the potential to form homo-oligomers in yeast. Moreover, all three sucrose transporters have the potential to interact with each other. The in vivo interaction between the functionally different sucrose transporters indicates that the membrane proteins are capable of forming oligomeric structures that, similar to mammalian glucose transporter complexes, might be of functional significance for regulation of transport. Using transgenic plants it will be tested whether the interaction of SUT proteins in yeast cells reflects the situation in planta. The analysis of LeSUT2 antisense plants will give an answer to the still open question whether their phenotype is consistent with a role of SUT2 in sugar sensing or sucrose transport.