Transgenic tobacco plants with improved cyanobacterial Rubisco expression but no extra assembly factors grow at near wild-type rates if provided with elevated CO2

Plant J. 2016 Jan;85(1):148-60. doi: 10.1111/tpj.13098.

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.

Keywords: CO2 concentration mechanism; Nicotiana tabacum; Rubisco; Synechococcus elongatus; chloroplast transformation; photosynthesis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Carbon Cycle
  • Carbon Dioxide / metabolism*
  • Chloroplasts / metabolism
  • Kinetics
  • Molecular Chaperones / genetics
  • Molecular Chaperones / metabolism*
  • Nitrogen / metabolism
  • Photosynthesis
  • Plants, Genetically Modified
  • Ribulose-Bisphosphate Carboxylase / genetics
  • Ribulose-Bisphosphate Carboxylase / metabolism*
  • Synechococcus / enzymology*
  • Synechococcus / genetics
  • Tobacco / enzymology
  • Tobacco / genetics
  • Tobacco / growth & development
  • Transgenes

Substances

  • Bacterial Proteins
  • Molecular Chaperones
  • RbcX protein, cyanobacteria
  • Carbon Dioxide
  • Ribulose-Bisphosphate Carboxylase
  • Nitrogen

Associated data

  • GENBANK/KM102745
  • GENBANK/KM102746
  • GENBANK/KT203393
  • GENBANK/KT203394