Often, while we may get useful compounds from the plants we grow, they can be difficult or costly to extract without specialized technologies. If one wants to only have a pure supply of a particular molecule, it has to be isolated from everything else that makes up the plant itself. And sometimes there are two compounds that you want to use and have to go through the even more complicated process of extracting them from each other and the plant at the same time. But with advancements in biotechnology and gene editing, there are other options available to accomplish that. In the case we’ll be discussing today, that involves removing one of those compounds from the plant entirely.
The Chicory of Plants
Chicory is a fairly useful plant, both for general food consumption that you may also know by the names of radicchio and endives and for the polysaccharide it makes in its roots that can act as a low calorie sweetener and as a prebiotic for making yogurt. This molecule is known as inulin and is highly sought after as a dietary fiber that is also beneficial to the growth of one’s gut microbiome. These applications have resulted in it being included in a variety of foods and in cosmetics for skincare to benefit all those positive microbes living on your face.
But chicory is also incredibly bitter, something certain people who eat it appear to enjoy. This bitterness is caused by a group of compounds with the fun name of sesquiterpene lactones (STLs) and these are even denser in the roots. The roots that contain the inulin we want to extract. These STLs are normally meant to help protect the plant from being eaten by burrowing insects, which gave chicory no safety when it came to us humans. But the extraction of the inulin invariably pulls out the STLs with it and results in a sweetener that is also highly bitter. Not exactly the sort of flavor you want in your juice or yogurt, though you could use it to make your black coffee even more bitter.
So growers would prefer to have two separate cultivars, one high in STLs and one low or entirely without STLs so that inulin can be extracted separately. But STL variance isn’t an observed trait in chicory and there are no known variants that are low in the compounds, so regular breeding of traits is unlikely to suddenly unearth this new phenotype. It is a possibility, but not a guarantee and a large investment of time would be required. Instead, we have CRISPR.
An All-Out STL Attack
At least some of the genes involved in biosynthesis of STLs have been identified, specifically those used in the first step of making the compound germacrene A synthase. Four separate versions of the synthase gene are known, one long and three short, with the long one primarily expressed in the leaves rather than in the roots. Past experiments using microRNA silencing proved that the amount of STLs could be at least partially reduced, but the exact involvement of each gene in the biosynthesis isn’t clear and it is unknown which in particular needs to be knocked out to prevent all STL production. So why not just hit all of them?
Using CRISPR-Cas9 and double strand breaks in order to cause misrepair of the specific gene regions, EU scientists in the chicory research group CHIC made a plant line with all four genes knocked out of their function and succeeded in almost completely eliminating STL synthesis. In response, other compounds in the plants were produced in a higher concentration, likely because cellular energy was diverted to making those instead with no STLs being made. The mutant lines also have the knockout mutation in both genome copies, which is referred to as the change being homozygous, and so the tedious process of self-pollinating plants to ensure a homozygous line is unneeded in this case.
This saves a lot of effort, as making homozygous versions for any change is necessary or the change could be lost in the subsequent generations. Additional lines were made with individual gene knockouts, so the contribution of each of the four genes to STL synthesis can be analyzed for future projects. Such as creating chicory lines that are even higher in STLs than normal and this can be additionally fine-tuned for occurring in the roots or the leaves as desired. The researchers hope that their null STL chicory can be used to increase collection of inulin in the future and allow for the healthier and gut microbe friendly sweetener to be used in more food products rather than higher calorie sweeteners.
In addition to these benefits to people’s general health from consuming lower calorie food products, there is also the potential in the market for a chicory with no bitterness. It may be against the taste of those who already love chicory as it is, but perhaps in the future we’ll see a new kind of chicory up for sale that will expand the amount of chicory lovers in the world, just of a different variety.
Photo CCs: Chicory stamen with pollen.jpg from Wikimedia Commons