A co-culture of E. coli and baker’s yeast now allows researchers to produce a specific group of plant hormones. Photo: David Baillot, UC San Diego Jacobs School of Engineering
An obscure group of plant hormones can now be obtained using a co-culture of E. coli and baker’s yeast. The development is set to accelerate research into these so-called strigolactones.
Normally, researchers tap hundreds of litres of xylem from poplar trees in order to study strigolactones, an important group of plant hormones. Now it can be done in the lab – using a kind of microbial cell factory: a co-culture of E. coli and baker’s yeast that together produce 125 times more strigolactones than previous laboratory attempts. Japanese and American biologists demonstrate this on 16 January in Science. This boost in production makes it considerably easier to study this obscure group of plant hormones in detail without requiring large quantities of plant material, the researchers write.
Germination signal
Plants use hormones to adapt to their environment and survive. Strigolactones play a crucial role in this, regulating a range of different traits, including shoot and root architecture, senescence, and drought tolerance. When phosphorus and nitrogen are scarce, plant roots secrete the hormones to establish symbiotic interactions with micro-organisms that help compensate for the nutrient deficit. Conversely, parasitic plants that attach to roots use the hormones as a germination signal or for chemotropic growth towards their host.
Tapping
Because strigolactones occur in plants only at low concentrations, research is difficult. Tapping around 340 litres of xylem from seven or eight poplar trees yields, after isolation and purification in the lab, only a small quantity of plant hormones. And for an average study you actually need around 1,000 litres of xylem, explains last author Yanran Li in a press release from the University of California.
Optimising
To change this, the biologists focused on two genes that are widespread among seed plants and are thought to produce strigolactones with essential biological functions: CYP722A and CYP722B. They then expressed these genes from sixteen different plant species – including poplar, pepper, pea, and peach – using a previously developed co-culture of E. coli and S. cerevisiae. Ultimately, they succeeded in optimising the output concentrations of strigolactones to 125 times higher than before.
With these increased concentrations, the researchers had sufficient material to determine the structure of several compounds produced in the process. One of these is 16-hydroxy-carlactonic acid, a substance that had already been described but whose function remained unclear. Elucidating its structure should help shed light on this.