Professor National Central University Taoyuan City, Taoyuan, Taiwan (Republic of China)
Body of Abstract: In rice, two class I small heat shock proteins (CI sHSPs), OsHsp16.9A and OsHsp18.0, shared 74% identity in their protein sequences but have different responses to stress signals. To investigate the function of these two proteins, we overexpressed or downregulated each gene in rice. For overexpression lines, OsHsp16.9A conferred increased thermotolerance in seeds, seedlings, and pollen grains, whereas OsHsp18.0 conferred thermotolerance only in seedlings. From chlorophyll contents and antioxidant enzyme activities, rice seedling leaves with OsHsp18.0 overexpression exhibited enhanced tolerance to Cd and Cu toxicity. Non-denaturing gel and mass spectrometry analyses of seed proteins revealed that OsHsp16.9A formed an oligomer with OsHsp101. We demonstrated that the interaction with OsHsp101 was necessary for OsHsp16.9A to confer thermoprotection, and glutamate residue 74 of OsHsp16.9A was responsible for the OsHsp16.9A–OsHsp101 interaction. Our results revealed that OsHsp16.9A and OsHsp18.0 executed different physiologic functions during the growth process of rice by cooperating with OsHsp101 or upregulating antioxidant enzymes.