The mitochondrial localized ascorbate peroxidase 5 (OsAPX5) functions in heat tolerance of rice

Rice yield is significantly impacted by elevated temperatures and heat damage, making it crucial to identify heat stress response genes and analyze their molecular mechanisms. In this study, we obtained a temperature-sensitive mutant, ts12, by screening an indica restorer line, R225 (wild type, WT), which was mutated through γ-ray irradiation. In the ts12 mutant, the glume fails to close properly under high-temperature conditions, resulting in a substantial reduction in the seed-setting ratio and grain yield. Cytological observations revealed that the reduction in transverse cell layers and the shortening of cell length contribute to the open glume phenotype in ts12. Map-based cloning and transgenic complementation studies indicated that TS12 encodes the ascorbate peroxidase OsAPX5, with a single nucleotide polymorphism (SNP) in ts12 leading to a truncated OsAPX5 protein. Furthermore, OsAPX5 was found to be widely expressed in the root, stem, leaf sheath, and young panicles, with its protein localized in the mitochondrion. Under high-temperature conditions, the ts12 mutant accumulates a higher concentration of reactive oxygen species (ROS) compared to the wild type (WT). Through yeast two-hybrid, luciferase, and pull-down assays, we demonstrated that OsAPX5 interacts with the rice glume development regulator OsMADS1. Additionally, the expression levels of OsMADS1, OsMADS5, and OsMADS34, which are associated with glume development, were significantly decreased in ts12 compared to the WT. Moreover, the OsAPX5-OsMADS1 interaction promoted the transcriptional activity of OsMADS1 and OsMADS34. These results indicate that OsAPX5 primarily influences ROS levels and the expression of OsMADS1, OsMADS5, and OsMADS34, thereby regulating the high-temperature stress response in rice.