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Published on May 20, 2009; 10.1104/pp.109.139816

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Received April 10, 2009
Accepted May 14, 2009

Plant physiological adaptations to the massive foreign protein synthesis occurring in recombinant chloroplasts

Julia Bally , Marie Nadai , Maxime Vitel , Anne Rolland , Raphael Dumain , and Manuel Dubald *

Bayer CropScience, 14-20 rue Pierre Baizet, BP 9163, 69263 Lyon Cedex 09, France; CNRS-UCBL-INSA-Bayer CropScience Joint Laboratory, UMR 5240, Bayer CropScience, 14-20 rue Pierre Baizet, F69263-Lyon-Cedex 9, France

* Corresponding author; email: manuel.dubald1{at}bayercropscience.com.

Genetically engineered chloroplasts have an extraordinary capacity to accumulate recombinant proteins. We have investigated in tobacco the possible consequences of such additional products on several parameters of plant development and composition. Plastid transformants were analyzed which express abundantly either bacterial enzymes, alkaline phosphatase (PhoA-S and PhoA-L) and 4-hydroxyphenyl pyruvate dioxygenase (HPPD), or a green fluorescent protein (GFP). In leaves, the HPPD and GFP recombinant proteins are the major polypeptides and accumulate to higher levels than ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Nevertheless, these engineered metabolic sinks do not cause a measurable difference in growth rate or photosynthetic parameters. The total amino acid content of transgenic leaves is also not significantly affected showing that plant cells have a limited protein biosynthetic capacity. Recombinant products are made at the expense of resident proteins. RuBisCO which constitutes the major leaf amino acid store is the most clearly and strongly down-regulated plant protein. This reduction is even more dramatic under conditions of limited nitrogen supply, whereas in contrast recombinant proteins accumulate to even higher relative levels. These changes are regulated post-transcriptionally since transcript levels of resident plastid genes are not affected. Our results show that plants are able to produce massive amounts of recombinant proteins in chloroplasts without profound metabolic perturbation, and that RuBisCO, acting as a nitrogen buffer is a key player in maintaining homeostasis and limiting pleiotropic effects.






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