Don’t get me wrong, plants have a lot of things going for them. However, as Groot’s fellow Galaxy Guardians can attest, vocabulary isn’t one of them. It can be hard to communicate with plants, even once you figure out their language. Take the plant abscisic acid (ABA) receptor, PYR1, for example. PYR1 communicates via ABA, a plant hormone that sounds the alarm for water stress and tells a plant to conserve water by closing its stomata.
Closing stomata helps plants keep water from escaping, but it also slows down their growth because CO2 can’t get in. Normally farmers want fast-growing crops with wide-open stomata, but when the weather forecast says no water for a while, it would be great if farmers could pass the word on to their crops. Unfortunately, ABA is too expensive to use every time there’s a dry spell.
Two years ago, the lab of Sean Cutler at UC Riverside discovered a new, potentially cheaper agonist, quinabactin, that could tell plants to hunker down for drought. However, quinabactin has yet to make it through the regulatory and commercialization gauntlet.
To find a quicker path to a practical drought signal, Cutler’s lab wondered if, instead of finding a new chemical that speaks PYR1’s language (i.e., an agonist), they could teach PYR1 to recognize a chemical that was already approved and available. Through a tour-de-force combination of screening, random mutagenesis, directed mutagenesis, and rational design – mostly affecting the receptor’s binding pocket – the team succeeded in making a new PYR1 variant that is deaf to ABA, but responds to mandipropamid instead. In one particularly striking experiment, mandipropamid was able to rescue arabidposis plants that otherwise would have died when left unwatered for 11 days, presumably during a lab retreat somewhere.
This approach to yelling “Drought!” to plants is a bit circuitous, of course. Farmers would have to be growing crops that had been engineered with the new receptor. Also, mandipropamid is a fungicide, and using it at every dry spell could help blight develop resistance to it.
However, the insight gained from this rewiring of the receptor could help the team teach it to recognize other chemicals too. In any case, this impressive bit of receptor re-engineering is definitely more effective than sitting out in the field with a guitar singing “It ain’t gonna rain no more no more”.
You can find the details on how plants have expanded their vocabulary with a new word for drought over in Nature, February 2015.