OsProDH Negatively Regulates Thermotolerance in Rice by Modulating Proline Metabolism and Reactive Oxygen Species Scavenging

BACKGROUND: Global warming threatens rice growth and reduces yields. Proline plays important roles in plant abiotic stress tolerance. Previous research demonstrated that engineering proline metabolism-related genes can enhance tolerance to freezing and salinity in Arabidopsis. OsProDH encodes a putative proline dehydrogenase and is a single copy gene in rice. However, whether OsProDH plays roles in abiotic stress in rice remains unknown. FINDINGS: Quantitative RT-PCR analysis revealed that OsProDH transcript contents were relatively higher in leaf blade and root tissues and the high temperature treatment repressed expression of OsProDH. The predicted OsProDH protein localized in mitochondria. Using the Oryza sativa ssp. japonica cultivar KY131, we generated OsProDH overexpression (OE) lines and knockout mutant lines using the CRISPR/Cas9 (CRI) system. Overexpression of OsProDH decreased proline content, while mutation of OsProDH increased proline content compared with that of KY131. The CRI and OE lines were respectively more resistant and sensitive to heat stress than KY131. Heat stress induced proline accumulation and mutation of OsProDH led to proline overproduction which reduced H(2)O(2) accumulation in the seedlings. CONCLUSIONS: OsProDH negatively regulates thermotolerance in rice. Our study provides a strategy to improve heat tolerance in rice via manipulating proline metabolism.