Phenotypic plasticity in response to temperature changes is critical for plant survival in diverse geographic environments and a constantly evolving global climate. A moderate increase in ambient temperature of just a few degrees can elicit dramatic adaptive responses in plant development, growth, metabolism and immunity, collectively referred to as thermomorphogenesis.

UC Riverside scientists have greatly improved the race to control plant responses to temperature on a rapidly warming planet. Key to this breakthrough is microRNAs (miRNAs), which play different roles in plant development, but whether and how miRNAs participate in thermomorphogenesis remains unclear.

UCR botany professor and study co-author Meng Chen said: “We found that plants without miRNA will not grow even if we increase the temperature, 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 preventing its target RNA from translating into another protein.”

The very modest temperature increases, from 21 to 27 degrees Celsius, were taken into account by the experts for this test. For comparison, the typical room temperature is 20 C. They have not done any research on stress responses. Without raising the temperature to a point where the plants would perish, they wanted to investigate the temperature sensing.

The scientists looked at mutated variants of Arabidopsis, a small flowering plant related to mustard and cabbage, with extremely low levels of miRNA. Without the miRNA, the mutated Arabidopsis would not be able to develop as it should in response to the temperature shift.

Xuemei Chen said: “We then did a genetic experiment. We asked if we could make additional mutations on the mutated Arabidopsis that are 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 and the plant’s heat-sensing ability.”

Scientists then looked for which miRNA molecules – out of more than 100 possibilities – are the essential ones in temperature response. They assumed that the levels of the responsible molecules would rise if the temperature did, but it didn’t.

Instead, the team looked at levels of target RNA molecules that were different in the original mutant Arabidopsis plant and in the second mutant plant they developed, taking into account that miRNA binds to target RNA molecules and this brakes.

Xuemei Chen said: “When we looked at this, we found that the targets of 14 miRNA had changed, and in addition to the targets, we also found the miRNA.”

Once the correct miRNA molecules were located, the team was able to piece together a complete picture of the temperature response. Auxin, a hormone that allows a response to what is sensed by stimulating plant development, and molecules that sense temperature are the two main components involved.

Meng Chen said: “There is miRNA between the sensor and the responder. Without it, plants can sense heat, but cannot respond to it by growing. It’s a gatekeeper that can shut down or allow plants to cope with environmental temperature changes.”

“Our discovery connected the dots between three elements found in all plants that are essential to plants’ responses to their environment.” This includes sensors that monitor temperature and light changes, hormones that stimulate plant growth, and miRNA that controls plant development .”

Magazine reference:

  1. Sang, Q., Fan, L., Liu, T. et al. MicroRNA156 conditions auxin sensitivity to enable growth plasticity in response to environmental changes in Arabidopsis. Nat Commun 14, 1449 (2023). DOI: 10.1038/s41467-023-36774-9