title: An engineered sorbitol cycle alters sugar composition, not growth, in transformed tobacco.
abstract: Many efforts have been made to engineer stress tolerance by accumulating polyols. Transformants that accumulate polyols often show growth inhibition, because polyols are synthesized as a dead-end product in plants that do not naturally accumulate polyols. Here, we show a novel strategy in which a sorbitol cycle was engineered by introducing apple cDNA encoding NAD-dependent sorbitol dehydrogenase (SDH) in addition to sorbitol-6-phosphate dehydrogenase (S6PDH). Tobacco plants transformed only with S6PDH showed growth inhibition, and very few transformants were obtained. In contrast, many transgenic plants with both S6PDH and SDH were easily obtained, and their growth was normal despite their accumulation of sorbitol. Interestingly, the engineered sorbitol cycle enhanced the accumulation of sucrose instead of fructose that was expected to be increased. Sucrose, rather than fructose, was also increased in the immature fruit of tomato plants transformed with an antisense fructokinase gene in which the phosphorylation of fructose was inhibited. A common phenomenon was observed in the metabolic engineering of two different pathways, showing the presence of homeostatic regulation of fructose levels.
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan.
authors.forename: Michihito
authors.initials: M
authors.lastname: Deguchi
authors.forename: Alan B
authors.initials: AB
authors.lastname: Bennett
authors.forename: Shohei
authors.initials: S
authors.lastname: Yamaki
authors.forename: Kunio
authors.initials: K
authors.lastname: Yamada
authors.forename: Koki
authors.initials: K
authors.lastname: Kanahama
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kanayama
mesh_terms: D016375:Antisense Elements (Genetics); D050260:Carbohydrate Metabolism; D005631:Fructokinases / Q000235:genetics; D007294:Inositol / Q000378:metabolism; D007064:L-Iditol 2-Dehydrogenase / Q000235:genetics; D018551:Solanum lycopersicum / Q000235:genetics; D013012:Sorbitol / Q000378:metabolism*; D013401:Sugar Alcohol Dehydrogenases / Q000235:genetics; D014026:Nicotiana / Q000254:growth & development / Q000378:metabolism*; D014170:Transformation, Genetic
chemical_list: D016375:Antisense Elements (Genetics); D007294:Inositol; D013012:Sorbitol; D013401:Sugar Alcohol Dehydrogenases; D007064:L-Iditol 2-Dehydrogenase; C022645:sorbitol-6-phosphate dehydrogenase; D005631:Fructokinases; C046173:fructokinase