title: Overexpression of plastid transketolase in tobacco results in a thiamine auxotrophic phenotype.
abstract: To investigate the effect of increased plastid transketolase on photosynthetic capacity and growth, tobacco (Nicotiana tabacum) plants with increased levels of transketolase protein were produced. This was achieved using a cassette composed of a full-length Arabidopsis thaliana transketolase cDNA under the control of the cauliflower mosaic virus 35S promoter. The results revealed a major and unexpected effect of plastid transketolase overexpression as the transgenic tobacco plants exhibited a slow-growth phenotype and chlorotic phenotype. These phenotypes were complemented by germinating the seeds of transketolase-overexpressing lines in media containing either thiamine pyrophosphate or thiamine. Thiamine levels in the seeds and cotyledons were lower in transketolase-overexpressing lines than in wild-type plants. When transketolase-overexpressing plants were supplemented with thiamine or thiamine pyrophosphate throughout the life cycle, they grew normally and the seed produced from these plants generated plants that did not have a growth or chlorotic phenotype. Our results reveal the crucial importance of the level of transketolase activity to provide the precursor for synthesis of intermediates and to enable plants to produce thiamine and thiamine pyrophosphate for growth and development. The mechanism determining transketolase protein levels remains to be elucidated, but the data presented provide evidence that this may contribute to the complex regulatory mechanisms maintaining thiamine homeostasis in plants.
authors: School of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom.
authors: Mahdi
authors: M
authors: Khozaei
authors: School of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom.
authors: Stuart
authors: S
authors: Fisk
authors: School of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom.
authors: Tracy
authors: T
authors: Lawson
authors: Max-Planck-Institut für Molekulare Pflanzenphysiologie, 114476 Potsdam-Golm, Germany.
authors: Yves
authors: Y
authors: Gibon
authors: Max-Planck-Institut für Molekulare Pflanzenphysiologie, 114476 Potsdam-Golm, Germany.
authors: Ronan
authors: R
authors: Sulpice
authors: Max-Planck-Institut für Molekulare Pflanzenphysiologie, 114476 Potsdam-Golm, Germany.
authors: Mark
authors: M
authors: Stitt
authors: School of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom.
authors: Stephane C
authors: SC
authors: Lefebvre
authors: School of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom rainc@essex.ac.uk.
authors: Christine A
authors: CA
authors: Raines
mesh_terms: D024322:Amino Acids, Aromatic / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology*; D002241:Carbohydrates / Q000737:chemistry; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D018548:Cotyledon / Q000187:drug effects / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005816:Genetic Complementation Test; D018525:Germination / Q000187:drug effects; D008954:Models, Biological; D010641:Phenotype; D010788:Photosynthesis / Q000187:drug effects; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D030821:Plants, Genetically Modified; D018087:Plastids / Q000201:enzymology*; D020005:Propanols / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000187:drug effects / Q000378:metabolism; D012765:Shikimic Acid / Q000378:metabolism; D013831:Thiamine / Q000494:pharmacology*; D013835:Thiamine Pyrophosphate / Q000494:pharmacology; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D014174:Transketolase / Q000378:metabolism*; D014994:Xylose / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D024322:Amino Acids, Aromatic; D002241:Carbohydrates; D020005:Propanols; D012333:RNA, Messenger; C492551:deoxyxylulose phosphate; C439395:1-phenylpropanol; D002245:Carbon Dioxide; D012765:Shikimic Acid; D002244:Carbon; D014994:Xylose; D014174:Transketolase; D013835:Thiamine Pyrophosphate; D013831:Thiamine