title: Decreased sucrose-6-phosphate phosphatase level in transgenic tobacco inhibits photosynthesis, alters carbohydrate partitioning, and reduces growth.
abstract: The aim of this work was to examine the role of sucrose-6-phosphate phosphatase (SPP; EC 3.1.3.24) in photosynthetic carbon partitioning. SPP catalyzes the final step in the pathway of sucrose synthesis; however, until now the importance of this enzyme in plants has not been studied by reversed-genetics approaches. With the intention of conducting such a study, transgenic tobacco plants with reduced SPP levels were produced using an RNA interference (RNAi) strategy. Transformants with less than 10% of wild-type SPP activity displayed a range of phenotypes, including those that showed inhibition of photosynthesis, chlorosis, and reduced growth rates. These plants had strongly reduced levels of sucrose and hexoses but contained 3-5 times more starch than the control specimens. The leaves were unable to export transient starch during extended periods of darkness and as consequence showed a starch- and maltose-excess phenotype. This indicates that no alternative mechanism for carbon export was activated. Inhibition of SPP resulted in an approximately 1,000-fold higher accumulation of sucrose-6-phosphate (Suc6P) compared to wild-type leaves, whereas the content of hexose-phosphates was reduced. Although the massive accumulation of Suc6P in the cytosol of transgenic leaves was assumed to impair phosphate-recycling into the chloroplast, no obvious signs of phosphate-limitation of photosynthesis became apparent. 3-Phosphoglycerate (3-PGA) levels dropped slightly and the ATP/ADP ratio was not reduced in the transgenic lines under investigation. It is proposed that in SPP-deficient plants, long-term compensatory responses give rise to the observed acceleration of starch synthesis, increase in total cellular Pi content, decrease in protein content, and related reduction in photosynthetic activity.
authors.affiliation: Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), Corrensstrasse 3, 06466 Gatersleben, Germany.
authors.forename: Shuai
authors.initials: S
authors.lastname: Chen
authors.forename: Mohammad
authors.initials: M
authors.lastname: Hajirezaei
authors.forename: Martin
authors.initials: M
authors.lastname: Peisker
authors.forename: Henning
authors.initials: H
authors.lastname: Tschiersch
authors.forename: Uwe
authors.initials: U
authors.lastname: Sonnewald
authors.forename: Frederik
authors.initials: F
authors.lastname: Börnke
mesh_terms: D050260:Carbohydrate Metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified; D034622:RNA Interference; D013395:Sucrose / Q000378:metabolism*; D014026:Nicotiana / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide; D013395:Sucrose; D010744:Phosphoric Monoester Hydrolases; C022697:sucrose-phosphatase