title: Transgenic tobacco plants with improved cyanobacterial Rubisco expression but no extra assembly factors grow at near wild-type rates if provided with elevated CO2.
abstract: Introducing a carbon-concentrating mechanism and a faster Rubisco enzyme from cyanobacteria into higher plant chloroplasts may improve photosynthetic performance by increasing the rate of CO2 fixation while decreasing losses caused by photorespiration. We previously demonstrated that tobacco plants grow photoautotrophically using Rubisco from Synechococcus elongatus, although the plants exhibited considerably slower growth than wild-type and required supplementary CO2 . Because of concerns that vascular plant assembly factors may not be adequate for assembly of a cyanobacterial Rubisco, prior transgenic plants included the cyanobacterial chaperone RbcX or the carboxysomal protein CcmM35. Here we show that neither RbcX nor CcmM35 is needed for assembly of active cyanobacterial Rubisco. Furthermore, by altering the gene regulatory sequences on the Rubisco transgenes, cyanobacterial Rubisco expression was enhanced and the transgenic plants grew at near wild-type growth rates, although still requiring elevated CO2 . We performed detailed kinetic characterization of the enzymes produced with and without the RbcX and CcmM35 cyanobacterial proteins. These transgenic plants exhibit photosynthetic characteristics that confirm the predicted benefits of introduction of non-native forms of Rubisco with higher carboxylation rate constants in vascular plants and the potential nitrogen-use efficiency that may be achieved provided that adequate CO2 is available near the enzyme.
authors.affiliation: Plant Biology and Crop Science, Rothamsted Research, Harpenden, AL5 2JQ, UK.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Occhialini
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA.
authors.forename: Myat T
authors.initials: MT
authors.lastname: Lin
authors.affiliation: Plant Biology and Crop Science, Rothamsted Research, Harpenden, AL5 2JQ, UK.
authors.forename: P John
authors.initials: PJ
authors.lastname: Andralojc
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA.
authors.forename: Maureen R
authors.initials: MR
authors.lastname: Hanson
authors.affiliation: Plant Biology and Crop Science, Rothamsted Research, Harpenden, AL5 2JQ, UK.|Lancaster Environment Centre, Lancaster University, Bailrigg, Lancaster, LA1 4YW, UK.
authors.forename: Martin A J
authors.initials: MA
authors.lastname: Parry
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D007700:Kinetics; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis; D030821:Plants, Genetically Modified; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism*; D046940:Synechococcus / Q000201:enzymology* / Q000235:genetics; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D019076:Transgenes
chemical_list: D001426:Bacterial Proteins; D018832:Molecular Chaperones; C522129:RbcX protein, cyanobacteria; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen
keywords: CO2 concentration mechanism; Nicotiana tabacum; Rubisco; Synechococcus elongatus; chloroplast transformation; photosynthesis