In-Cheol Jang^1,a, Se-Jun Oh^1,a, Ju-Seok Seo^2,a, Won-Bin Choi¹, Sang Ik Song¹, Chung Ho Kim³, Youn Shic Kim⁴, Hak-Soo Seo², Yang Do Choi², Baek Hie Nahm^1,4 and Ju-Kon Kim^*,1,4

¹ Department of Biological Science, Myongji University, Yongin 449-728, Korea (I.-C.J., S.-J.O., W.-B.C., S.I.S., B.H.N., J.-K.K.);
² School of Agricultural Biotechnology, Seoul National University, Suwon 441-744, Korea (J.-S.S., H.-S.S., Y.D.C.);
³ Department of Food and Nutrition, Seowon University, Chongju 361-742, Korea (C.H.K.); and
⁴ Genomics and Genetics Institute, GreenGene BioTech, Yongin 449-728, Korea (Y.S.K., B.H.N., J.-K.K.)

^*Corresponding author
^a These authors contributed equally to the paper.

Abstract
Trehalose plays an important role in stress tolerance in plants. Trehalose-producing, transgenic rice (Oryza sativa) plants were generated by the introduction of a gene encoding a bifunctional fusion (TPSP) of the trehalose-6-phosphate (T-6-P) synthase (TPS) and T-6-P phosphatase (TPP) of Escherichia coli, under the control of the maize (Zea mays) ubiquitin promoter (Ubi1). The high catalytic efficiency (Seo et al., 2000) of the fusion enzyme and the single-gene engineering strategy make this an attractive candidate for high-level production of trehalose; it has the added advantage of reducing the accumulation of potentially deleterious T-6-P. The trehalose levels in leaf and seed extracts from Ubi1::TPSP plants were increased up to 1.076 mg g fresh weight^-1. This level was 200-fold higher than that of transgenic tobacco (Nicotiana tabacum) plants transformed independently with eitherTPS or TPP expression cassettes. The carbohydrate profiles were significantly altered in the seeds, but not in the leaves, of Ubi1::TPSP plants. It has been reported that transgenic plants with E. coli TPSand/or TPP were severely stunted and root morphology was altered. Interestingly, our Ubi1::TPSP plants showed no growth inhibition or visible phenotypic alterations despite the high-level production of trehalose. Moreover, trehalose accumulation in Ubi1::TPSP plants resulted in increased tolerance to drought, salt, and cold, as shown by chlorophyll fluorescence and growth inhibition analyses. Thus, our results suggest that trehalose acts as a global protectant against abiotic stress, and that rice is more tolerant to trehalose synthesis than dicots.