The Gene PbTMT4 from Pear (pyrus Bretschneideri) Mediates Vacuolar Sugar Transport and Strongly Affects Sugar Accumulation in Fruit.

Tonoplast monosaccharide transporters (TMTs) play important roles in vacuolar sugar accumulation in plants. In this study, six TMT genes (PbTMT1-6) were identified in the Pyrus bretschneideri genome database, and their expression profiles were correlated with soluble sugar contents during the pear (P. bretschneideri cv. Ya Li) fruit development process. Subsequently, PbTMT4 was identified as a strong contributor to fructose, glucose and sucrose accumulation in fructescence of pears. Heterologous expression of PbTMT4, in the hexose transporter-deficient yeast strain EBY.VW4000, facilitated growth in media containing low levels of glucose, fructose, sucrose or sorbitol. In addition, PbTMT4-transformed tomato plants flowered and bore fruit significantly earlier than wild-type (WT) plants, and glucose and fructose levels in mature tomatoes were increased by about 32 and 21% compared with those in WT plants. However, no obvious alterations in sucrose content, plant height and weight per fruit were observed. Finally, subcellular localization experiments in transformed Arabidopsis plants showed that PbTMT4 is localized to tonoplast vesicles of protoplasts. These preliminary results suggest that PbTMT4 participates in vacuolar accumulation of sugars, and thus affects plant growth and development.