OsProDHNegatively 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 inArabidopsis.OsProDHencodes a putative proline dehydrogenase and is a single copy gene in rice. However, whetherOsProDHplays roles in abiotic stress in rice remains unknown. Findings Quantitative RT-PCR analysis revealed thatOsProDHtranscript contents were relatively higher in leaf blade and root tissues and the high temperature treatment repressed expression ofOsProDH. The predicted OsProDH protein localized in mitochondria. Using theOryza sativa ssp. japonicacultivar KY131, we generatedOsProDHoverexpression (OE) lines and knockout mutant lines using the CRISPR/Cas9 (CRI) system. Overexpression ofOsProDHdecreased proline content, while mutation ofOsProDHincreased 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 ofOsProDHled to proline overproduction which reduced H(2)O(2)accumulation in the seedlings. Conclusions OsProDHnegatively regulates thermotolerance in rice. Our study provides a strategy to improve heat tolerance in rice via manipulating proline metabolism.