Journal Article

A new synthetic biology approach allows transfer of an entire metabolic pathway from a medicinal plant to a biomass crop

Erban, Alexander, Karcher, Daniel, Fuentes, Paulina, Zhou, Fei, Kopka, Joachim, Bock, Ralph

2016

Overview

Artemisinin-based therapies are the only effective treatment for malaria, the most devastating disease in human history. To meet the growing demand for artemisinin and make it accessible to the poorest, an inexpensive and rapidly scalable production platform is urgently needed. Here we have developed a new synthetic biology approach, combinatorial supertransformation of transplastomic recipient lines (COSTREL), and applied it to introduce the complete pathway for artemisinic acid, the precursor of artemisinin, into the high-biomass crop tobacco. We first introduced the core pathway of artemisinic acid biosynthesis into the chloroplast genome. The transplastomic plants were then combinatorially supertransformed with cassettes for all additional enzymes known to affect flux through the artemisinin pathway. By screening large populations of COSTREL lines, we isolated plants that produce more than 120 milligram artemisinic acid per kilogram biomass. Our work provides an efficient strategy for engineering complex biochemical pathways into plants and optimizing the metabolic output. Malaria is by far the most devastating tropical disease in the world. It affects hundreds of millions of people – mainly in Africa and Asia – with almost half a million deaths every year. The most effective therapies against malaria all include the drug artemisinin, which is naturally found in an Asian plant called Artemisia annua. Unfortunately, the artemisinin content of A. annua plants is relatively low and the demand for this drug outstrips the supply of the plant. The costly production process makes artemisinin-based treatments inaccessible to many of the people in the most badly affected regions, and so researchers have been trying to find new ways to produce this drug. Genetically modifying crop plants, such as tobacco, to produce artemisinin or related compounds could potentially provide a more sustainable and cheaper source of the drug. Inside plant cells, a structure called the nucleus contains DNA that encodes most of a plant’s genes, but compartments called mitochondria and chloroplasts also contain some DNA. Existing methods to genetically modify plants are able to insert a few genes into either the nucleus or the chloroplasts at a time. However, the production of artemisinin in A. annua involves many different genes that act at different stages of the process, and the precise roles played by many of them remain unclear. Fuentes et al. developed a new approach to insert many of the A. annua genes involved in artemisinin production into tobacco plants at the same time, instead of one-by-one. The new method, referred to as COSTREL, takes advantage of the researchers’ ability to insert new genes into both the nucleus and the chloroplast of the tobacco plants. In the first step, Fuentes et al. inserted a core set of genes that are essential to make artemisinin into the chloroplast. This enabled the plants to produce a molecule called artemisinic acid, which the researchers can extract from the plants and convert into artemisinin by simple chemical reactions. After testing different arrangements of the genes in the chloroplast, the plant line that had the highest levels of artemisinic acid was used to introduce a set of “accessory” genes into the nuclear DNA. These accessory genes are not strictly required to make the drug, but they help to regulate the process in a largely unknown manner. The experiments generated hundreds of genetically modified plant lines that each have different combinations of the accessory genes. Fuentes et al. examined these lines and were able to identify plants that could produce large amounts of artemisinic acid. Therefore, these findings lay the foundations for a cheap way to produce this life-saving drug in tobacco. In the future, the COSTREL method developed by Fuentes et al. could also be used to genetically engineer other complex biochemical processes into plants.

• Publisher: eLife Sciences Publications Ltd,eLife Sciences Publications, Ltd
• Subject: Acids / Alcohol / Antimalarials - metabolism / Artemisinin / Artemisinins - metabolism / Biochemistry / Biomass / Biosynthesis / Chloroplasts / combinatorial transformation / Cytochrome / Enzymes / Genomes / Malaria / Medicinal plants / metabolic engineering / Metabolic Engineering - methods / Metabolic Networks and Pathways - genetics / Metabolism / Metabolites / Molecular Biology - methods / Nicotiana - genetics / Nicotiana - metabolism / Nicotiana tabacum / Plant Biology / Plants, Genetically Modified - genetics / Plants, Genetically Modified - metabolism / Plants, Medicinal - genetics / Plants, Medicinal - metabolism / plastid transformation / Synthetic biology / Synthetic Biology - methods / Tobacco / Yeast