Trehalose-producing transgenic tobacco plants show improved growth performance under drought stress

Trehalose plays a role in drought stress resistance in a variety of organisms, including the extremely drought-tolerant <<resurrection plants>>. Transgenic tobacco plants that produce trehalose were engineered by introduction of the Escherichia coli otsA and otsB genes, encoding trehalose-6-P synthase and trehalose-6-P phosphatase, respectively. The introduction of these genes had a pronounced effect on plant morphology and growth performance under drought stress. The transgenic Ots plants had larger leaves and altered stem growth. When grown under drought stress imposed by limiting water supply, the two transgenic tobacco lines Ots2 and Ots5 yielded total dry weights that were 28% and 39% higher than those of wild-type tobacco. These increases in dry weight were due mainly to increased leaf production: leaf dry weights were up to 85% higher for the best trehalose accumulator, Ots5. No significant differences were observed under well-watered conditions. Chlorophyll fluorescence analysis of drought-stressed plants showed a higher photochemical quenching (q(Q)) and a higher ratio of variable fluorescence over maximal fluorescence (F-v/F-m), indicating a more efficient photosynthesis. The Ots5 plants showed more negative leaf osmotic potentials than wild-type plants, particularly under drought stress, as well as higher levels of nonstructural carbohydrates; Ots2 plants showed intermediate values. Detached leaves from young, well-watered Ots plants had a better capacity than wild-type leaves to retain water when air-dried. They had lower osmotic potentials than wild-type leaves, and higher levels of glucose, fructose and sucrose.