The first step in their process was to transfer the genes of the artemisinic acid pathway’s core set of enzymes into the chloroplast genome of tobacco plants, generating what are known as transplastomic plants.
The team then used their best transplastomic tobacco plant line to introduce an additional set of genes into its nuclear genome, generating the COSTREL lines. These remaining genes encode factors that increase the synthesis, or generation, of the acid in ways that are still largely unknown.

“While the artemisinic acid pathway in A. annua is confined to the glandular hairs on the plant, leading to low yields of artemisinin, our COSTREL tobacco lines produce it in their chloroplasts and therefore the whole leaf,” says lead author and postdoctoral researcher Paulina Fuentes.
“We generated over 600 engineered tobacco plant lines that harbour different combinations of these additional genes, and analysed them in terms of the amounts of artemisinic compounds they acquired,” Fuentes explains.