Current Biology
Volume 27, Issue 19, 9 October 2017, Pages 3034-3041.e3
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Horizontal Transfer of a Synthetic Metabolic Pathway between Plant Species

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Highlights

  • Design of a synthetic operon encoding the biosynthetic pathway for astaxanthin

  • Introduction into tobacco plastids directs high-level synthesis of astaxanthin

  • Horizontal transfer of the engineered plastids across graft junctions into a tree

  • Horizontal genome transfer facilitates plastid engineering in recalcitrant species

Summary

Transgene expression from the plastid (chloroplast) genome provides unique advantages, including high levels of foreign protein accumulation, convenient transgene stacking in operons, and increased biosafety due to exclusion of plastids from pollen transmission [1, 2]. However, applications in biotechnology and synthetic biology are severely restricted by the very small number of plant species whose plastid genomes currently can be transformed [3, 4]. Here we report a simple method for the introduction of useful plastid transgenes into non-transformable species. The transgenes tested comprised a synthetic operon encoding three components of a biosynthetic pathway for producing the high-value ketocarotenoid astaxanthin in the plastids of the cigarette tobacco, Nicotiana tabacum. Transplastomic N. tabacum plants accumulated astaxanthin to up to 1% of the plants’ dry weight. We then used grafting, a procedure recently shown to facilitate horizontal genome transfer between plants [5, 6, 7], to let the transgenic chloroplast genome move across the graft junction from N. tabacum plants into plants of the nicotine-free tree species Nicotiana glauca. Transplastomic N. glauca trees expressing the synthetic pathway were recovered at high frequency, thus providing a straightforward method for extension of the transplastomic technology to new species.

Keywords

horizontal genome transfer
horizontal gene transfer
synthetic biology
plastid transformation
carotenoid biosynthesis
astaxanthin
ketocarotenoid
isoprenoid biosynthesis
Nicotiana tabacum
Nicotiana glauca

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2

Present address: Nanjing University of Science and Technology, School of Chemical Engineerings, Xiaolingwei Street 200, 210094 Nanjing, China

3

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