High accumulation of heterologous proteins expressed from the plastid genome has sometimes been reported to result in compromised plant phenotypes. Comparisons of transplastomic plants to wild-type (WT) are typically made in environmentally controlled chambers with relatively low light; little is known about the performance of such plants under field conditions. Here, we report on two plastid-engineered tobacco lines expressing the bacterial cellulase Cel6A. Field-grown plants producing Cel6A at ~20% of total soluble protein exhibit no loss in biomass or Rubisco content and only minor reductions in photosynthesis compared to WT. These experiments demonstrate that, when grown in the field, tobacco possesses sufficient metabolic flexibility to accommodate high levels of recombinant protein by increasing total protein synthesis and accumulation and/or by reallocating unneeded endogenous proteins. Based on current tobacco cultivation practices and readily achievable recombinant protein yields, we estimate that specific proteins could be obtained from field-grown transgenic tobacco plants at costs three orders of magnitude less than current cell culture methods.
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All data generated or analysed during this study are included in this published article and its Supplementary information.
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We thank L.V. Richter for providing advice and labororatory training to J.A.S. We also thank D. Drag and B. Harbaugh for managing the field sites and cultivating the plants.
The authors declare no competing interests.
Peer review information: Nature Plants thanks Francis Quétier and other, anonymous, reviewers for their contribution to the peer review of this work.
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