OsOFP3 Negatively Regulates Heat Stress Tolerance by Modulating H2O2 Homeostasis and Stomatal Aperture in Rice

Rice (<i>Oryza sativa</i>) is a staple crop that is highly susceptible to heat stress (HS), which severely impairs growth and yield. In this study, we identified the rice Ovate Family Protein <i>OsOFP3</i> as a novel negative regulator in response to heat. Our results demonstrate that the expression of <i>OsOFP3</i> is suppressed at both the transcriptional and protein levels under HS. Overexpression of <i>OsOFP3</i> significantly reduces the survival rate of rice seedlings under HS and exacerbates chlorophyll degradation, membrane damage, and the accumulation of reactive oxygen species (H₂O₂ and O₂^-). In contrast, <i>OsOFP3</i> mutants exhibit enhanced heat tolerance. Moreover, <i>OsOFP3</i>-overexpressing plants display increased stomatal opening and decreased stomatal closure under HS. Molecular interaction analysis further reveals that OsOFP3 interacts with the C-terminal domain of OsHTAS, a known positive regulator of heat tolerance encoding an E3 ubiquitin ligase, and this interaction depends on the RING domain of OsHTAS. Taken together, our findings indicate that <i>OsOFP3</i> negatively regulates rice heat tolerance by disrupting ROS homeostasis, inhibiting stomatal closure, and potentially antagonizing the OsHTAS-mediated signaling pathway. This research provides new insights into the molecular mechanisms underlying HS tolerance in rice.