Heat stress mediated structural and functional change of tetratricopeptide repeat-containing thioredoxin, OsTDX, in Oryza sativa.

Heat stress due to global warming adversely affects plant physiology and metabolism, significantly reducing agricultural productivity. Plants have evolved various adaptive mechanisms to cope with such stresses, involving a range of heat stress-responsive proteins. This study investigates the molecular functions and structural changes of OsTDX (Oryza sativa TPR repeat-containing thioredoxin) in rice under heat stress, focusing on its roles as a disulfide reductase and molecular chaperone. OsTDX, sharing a 52 % overall amino acid identity with AtTDX, predominantly forms high molecular weight (HMW) complexes under heat stress conditions. Functional assays revealed that OsTDX exhibited increased disulfide reductase activity in a dose-dependent manner and significantly enhanced holdase chaperone activity, particularly under specific heat stress conditions (60 °C). The structural shift from low molecular weight (LMW) to HMW forms was accompanied by increased hydrophobicity, as indicated by bis-ANS fluorescence intensity measurements. In conclusion, OsTDX exhibits dual functions as a disulfide reductase and a holdase chaperone, with its chaperone activity significantly enhanced under heat stress through structural changes to HMW complexes. These findings contribute to understand the molecular mechanisms of heat tolerance in rice and highlight the potential role of OsTDX in the development of heat-tolerant crops to address crop yield declines due to global warming.