A new tool could make it easier to study scarce plant molecules. Researchers have developed so-called microbial cell factories -- using E. coli and yeast -- to produce a special class of plant hormones, known as strigolactones, at unprecedented levels. By amplifying production of strigolactones, which occur in such low amounts in plants, researchers now have the ability to study these elusive plant molecules in much greater depth than before. The work could help improve sustainable agricultural practices by offering deeper insights into how plants make and use their natural hormones to adapt and survive.

To investigate, the researchers tested what happens with the sister genes in a microbial cell factory, made by co-culturing E. coli and Baker's yeast, that they previously developed. With this platform, they expressed the CYP722A and CYP722B genes from 16 different plant species, including poplar, pepper, pea and peach. Through further metabolic engineering, first author Anqi Zhou, a chemical engineering Ph.D. student in Li's lab, found efficient ways to optimize the output concentrations of strigolactones, more than 125-fold than before. That enhanced concentration gives the researchers enough material to figure out the structure of any resulting compounds, which could potentially play an important role in plant physiology. And one such important molecule could be the novel compound produced by CYP722A or CYP722B: a strigolactone called 16-hydroxy-carlactonic acid (16-OH-CLA).

Interestingly, when the researchers looked for 16-OH-CLA in plants, they only detected it in the shoots and not the roots, unlike all the other known strigolactones. What's more, the compound isn't present at all times. For annual plants like pepper or the common pea, the compound disappears once the plant is mature and developed. For trees like poplar, it's seasonal. Although the specific function of 16-OH-CLA remains elusive, its common presence within seed plants and in an unusual plant region suggests that it may play a critical, yet underappreciated role, in plant signaling or adaptation to environmental challenges. Thanks to the new engineering approach, researchers will easily have the quantities they need to dig deeper -- which is exactly what Li and the team are working on now.