Analysis of vacuolar sugar transport

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Sugar accumulation in vacuoles is of high importance for plant development and physiology, as well as of agronomic relevance. However, corresponding tonoplast located transport proteins have not been identified on the molecular level up to now. We identified a first vacuolar sugar transporter (TMT, tonoplast monosaccharide transporter) from Arabidopsis on both, the molecular and functional level. TMT proteins represent a small subgroup of monosaccharide transporters in Arabidopsis comprising 3 isoforms. All TMT proteins reside in the tonoplast and exhibit a unique molecular structure. Attmt1 and 2 genes exhibit a tissue specific expression pattern and are up-regulated upon cold-, salt- and drought stress or monosaccharide application. tmt knock out plants show reduced vacuolar glucose uptake and lack, in contrast to Wt plants, the ability to accumulate monosaccharides upon cold induction. Here we want to extend our analysis on the function and regulation of TMT proteins. In particular, we are interested in analyzing structural determinants leading to a tonoplast localization of TMT proteins, we will decipher a putative function of the uniquely large centrally located loop domain and we will identify loop binding proteins. In addition, the physiological impact of vacuolar sugar transport during adaptation to cold temperatures will be clarified by using a systems biological approach. For this we will compare corresponding metabolic-, transcriptomic- and proteomic changes in Wt plants, in tmt knock out-, and in tmt overexpressor lines upon cold adaptation.