Phenotypic plasticity in response to temperature changes is critical for the survival of plants in diverse geographical environments and a constantly evolving global climate. A moderate increase in the ambient temperature of only a few degrees can elicit dramatic adaptive responses in plant development, growth, metabolism, and immunity, collectively called thermomorphogenesis.
UC Riverside scientists have significantly advanced the race to control plant responses to temperature on a rapidly warming planet. Key to this breakthrough is MicroRNA (miRNAs), which play diverse roles in plant development, but whether and how miRNAs participate in thermomorphogenesis remains ambiguous.
UCR botany professor and study co-author Meng Chen said, “We found that without miRNA, plants will not grow, even if we raise temperatures, even in the presence of added growth hormones.”
UCR botany professor and study co-author Xuemei Chen said, “MiRNA inhibits the production of its target RNA by inducing a cleavage in its target or by inhibiting its target RNA from translating into another protein.”
The very modest temperature rises, from 21 to 27 degrees Celsius, was considered for this test by the experts. For comparison, the typical room temperature is 20 C. They did not examine stress reactions. Without increasing the temperature to a point where the plants would perish, they wished to examine temperature sensing.
The scientists looked at mutant variants of Arabidopsis, a tiny flowering plant related to mustard and cabbage, with extremely low amounts of miRNA. Without the miRNA, the mutant Arabidopsis could not develop as it should have in response to the temperature shift.
Xuemei Chen said, “We then did a genetics experiment. We asked whether we could make additional mutations on the mutant Arabidopsis deficient in making miRNAs and restore their ability to sense temperature.”
“The second experiment worked perfectly, and it revealed a gene responsible for restoring miRNA levels as well as the plant’s heat sensing abilities.”
Scientists next searched for which miRNA molecules — out of more than 100 possibilities — are the essential ones in temperature response. They assumed levels of the responsible molecules would increase as temperatures did, but it didn’t happen that way.
The team instead looked at target RNA molecule levels that were different in the original mutant Arabidopsis plant and in the second mutant plant they developed, keeping in mind that miRNA binds to and inhibits target RNA molecules.
Xuemei Chen said, “Looking at this, we found the targets of 14 miRNA changed, and alongside the targets, we also found the miRNA.”
Once the correct miRNA molecules were located, the team could piece together a complete picture of temperature responsiveness. Auxin, a hormone that allows a reaction to what has been sensed by boosting plant development, and molecules that sense temperature are the two key components involved.
Meng Chen said, “In between the sensor and the responder is miRNA. Without it, plants can sense heat but cannot respond to it by growing. It is a gatekeeper that can shut down — or allow — plants to deal with environmental temperature changes.”
“Our discovery connected the dots between three elements found in all plants that are key for plant responses to their environments. “This includes sensors that monitor temperature and light changes, hormones that drive plant growth, and miRNA that controls plant development.”