###### Abstract  
Wheat cultivation makes an important contribution to human nutrition. Trehalose synthesis plays a role in the tolerance to drought stress. A bifunctional TPS-TPP enzyme gene from yeast was used to obtain transgenic wheat plants to increase trehalose synthesis. Mature wheat embryos were transformed using pGreen r29A:TPS1-TPS2 or pGreen 35S:TPS1-TPS2 constructs. The transgene presence in mature leaves of T3 plants was confirmed by sequencing a PCR fragment of the inserted transgene. Transgenic and NT plants were submitted to drought stress for eight days. Transformed wheat lines retained a higher relative water content than NT plants during drought stress, and the Rubisco activity was unaffected. Plants transformed with the 35S construct showed a lower photosynthetic rate and lower fructose 1-6-bisphosphatase (FBPase) activity during drought, suggesting that constitutive trehalose and sucrose synthesis caused a reduced ribulose 1,5-bisphosphate (RuBP) regeneration. Lines transformed with the rd29A promoter showed a higher photosynthetic rate after eight days of drought, as the RuBP regeneration was unaffected. Transgenic wheat plants had higher biomass and grain weight than NT plants after drought. These results suggest that trehalose synthesis improves photosynthesis during stress and induces changes in the activity of some Calvin-cycle enzymes, reflected in plant metabolism and growth.  
carbohydrate; drought; photosynthesis; trehalose; wheat transformation +
Footnote †: journal: Physics Letters B  
0000-0002-0002-3300][PERSON]  
0000-0002-3313-7267  
0000-0002-3310-0002-3310-0002-310-0002-310-0002-310-0002-3100-002-310  
6-phosphate, generating trehalose [6]. Several studies have demonstrated that trehalose plays an essential role in the plant response to abiotic stress [7; 8; 9; 10; 11; 12]. Despite having many copies of the _tps_ and _tpp_ genes, higher plants do not accumulate trehalose; nonetheless, the gene expressions of plant TPS and TPP are induced by abiotic stress, such as salt and drought stress [13; 14; 15].  
Some studies have shown that the induction of trehalose synthesis in plants by inserting genes for TPS and TPP enzymes can affect plant metabolism and physiology differently. For example, several studies found that the overexpression of microbial TPS boosts tolerance against abiotic stress [10; 16; 17; 18], while others have reported disturbances in plant growth and morphology [17; 18; 19]. This effect can be attributed to increased levels of T6P, a key metabolite in sugar metabolism regulation [20; 21]. Nonetheless, improved photosynthesis was found in tobacco and tomato caused by the overexpression of a _TPS1_ gene from _Saccharomyces cerevisiae_, as it increased the chlorophyll and starch content [17; 18].  
[PERSON] et al. (2007) [22] synthesized a bifunctional TPS-TPP enzyme from the fusion of _S. cerevisiae TPS1_ and _TPS2_ genes. This bifunctional enzyme prevents T6P accumulation in _Arabidopsis thaliana_, generating abiotic-stress-tolerant plants without morphological alterations [22]. The overexpression of a similar fusion _TPSP_ gene from _Escherichia coli_ induced a higher photosynthetic rate during abiotic stress in rice and tomatoes [10; 16]. Although an increased trehalose synthesis leads to improved photosynthetic performance under abiotic stress, little is known about how sugar synthesis in the Calvin cycle is affected by the modification of trehalose metabolism in plants. For example, in tobacco plants, the overexpression of a _TPS_ gene from _E. coli_ increased the Rubisco activity, but no changes in the activity of other Calvin-cycle enzymes were found [23]. In this work, we transformed wheat plants for the overexpression of a bifunctional TPS-TPP enzyme to evaluate the changes in photosynthesis, activity of the Calvin cycle, and sugar synthesis enzymes in plants subjected to drought stress.