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Field-grown tobacco plants maintain robust growth while accumulating large quantities of a bacterial cellulase in chloroplasts

Abstract

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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Acknowledgements

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.

Author information

J.M.M. and S.P.L. supervised planting and harvesting of growth chamber and field trials and made photosynthetic measurements. J.A.S. performed immunoblots, performed statistical analyses and produced all figures. S.P.L., M.R.H. and B.A.A. conceived of the project. All authors participated in writing the manuscript. All authors planned research and discussed results. This work is supported in part by the AFRI NIFA Fellowships Grant Program (2018-67011-28027/project accession No. 1015534) awarded to J.A.S. from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the US Department of Agriculture.

Correspondence to Beth A. Ahner.

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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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Supplementary information

Supplementary Information

Supplementary Figs. 1 and 2, and Supplementary Tables 1–4.

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Supplementary Datasets

Data generated for Figs. 1b–d, 2c,e and 3 and Supplementary Figs. 1a–c and 2.

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Fig. 1: Biomass accumulation and photosynthetic rate of field-grown tobacco.
Fig. 2: Cel6A and Rubisco protein quantification from leaf tissues.
Fig. 3: Comparative trials of protein allocation among Cel6A, Rubisco and all other endogenous soluble proteins.
Fig. 4: Hypothesized strategies for resource allocation and adaptation to foreign protein accumulation in transplastomic tobacco grown under different conditions.