9--epoxycarotenoid dioxygenase 1 confers heat stress tolerance in rice seedling plants.

High temperature is one of the main constraints affecting plant growth and development. It has been reported that abscisic acid (ABA) synthesis gene () positively regulates plant resistance to salt, cold, and drought stresses. However, little is known about the function of the gene in heat tolerance of rice. Here, we found that was a heat stress inducible gene. Rice seedlings overexpressing showed enhanced heat tolerance with more abundant ABA content, whereas the knockout mutant accumulated less ABA and showed more sensitive to heat stress. Under heat stress, increased expression of could reduce membrane damage and reactive oxygen species (ROS) level of plants, and elevate the activity of antioxidant enzymes. Moreover, real time-quantitative PCR (RT-qPCR) analysis showed that overexpression of significantly activated the expression of genes involved in antioxidant enzymes, ABA signaling pathway, heat response, and defense. Together, our results indicate that positively regulates heat tolerance of rice seedling by raising endogenous ABA contents, which leads to the improved antioxidant capacity and activated expression of heat and ABA related genes.