Plants have to deal with different environmental conditions to survive. With 2014 being on record as the warmest year ever, the most recent challenges included high temperatures and less water supply, which can drastically lower yield and end up costing farmers billions.
In the event of a drought, plants naturally produce a stress hormone called abscisic acid (ABA), which inhibits plant growth and cuts back on water requirements for a plant. To do this, ABA turns on a special protein when it binds to it. With the protein turned on, guard cells on leaves are closed, reducing water loss that then helps a plant to survive despite the reduced availability of water.
ABA, however, is expensive to produce so it's not practical to simply use it as a spray for crops. Not to mention that the hormone is sensitive to light and quickly inactivates once it gets inside the plant's cells. The other course of action that research groups have explored is to develop a synthetic form of ABA that will mimic how the hormone functions. This, though, will also be costly and lengthy to develop.
A team led by scientists from the University of California, Riverside took a different approach by taking advantage instead of an agrochemical that is already in use for controlling fungal pathogens in a number of fruits and vegetables. Working with Arabidopsis, which is a model plant, and a tomato plant, researchers developed a version of the special proteins ABA bind to, engineering the said proteins to activate when encountering the agrochemical mandipropamid and not ABA.
The researchers showed that when mandipropamid was sprayed, the reprogrammed plants effectively closed guard cells in their leaves much like the same effect achieved when ABA binds to the special proteins. With guard cells closed, water loss is prevented and the reprogrammed plants survived a simulated drought.
"We successfully repurposed an agrochemical for a new application by genetically engineering a plant receptor -- something that has not been done before," said Sean Cutler, the corresponding author for the study. "We anticipate that this will allow other agrochemicals to control other useful traits -- such as disease resistance or growth rates."
The study, published in the journal Nature, was partly supported by Sygenta and the National Science Foundation. Sygenta manufactures mandipropamid marketed as Revus.
Other researchers involved in the study include Sang-Youl Park, Brian Volkman, Francis Peterson, Jin Yao and Assaf Mosquna. Volkman and Peterson are with the Medical College of Wisconsin.