| Summary: | 碩士 === 國立臺灣大學 === 生化科技學系 === 105 === It has been shown that the effect of acquired thermotolerance is extended by the interplay between Heat-Stress-Associated 32-kD protein (HSA32) and Heat Shock Protein 101 (HSP101) in Arabidopsis and rice. HSP101 promotes the production of HSA32, and HSA32 reduces the degradation of HSP101. The molecular action of HSA32 is unknown. It had been proposed that HSA32 may participate in sulfur metabolism due to sequence similarity with archaea (2R)-phospho-3-sulfolactate synthase (PSL synthase). Moreover, this study identified found a highly conserved 3''-phosphoadenosine-5''-phosphosulfate (PAPS)-binding motif sequence of HSA32 in higher plants. PAPS is an activated sulfur donor for the sulfation reaction catalyzed by sulfotransferases. Thus, HSA32 probably acts as a sulfotransferase. Choline sulfate is synthesized by choline sulfotransferase whose activity had been detected but had not been cloned yet. Therefore, I hypothesized that HSA32 catalyzes the production of choline sulfate under heat stress to suppress the degradation of HSP101. However, the result of UPLC-MS/MS analysis showed that choline sulfate can be detected in hsa32-1 to a level as high as in wild type under both normal and heat stress condition. The result indicates that HSA32 is not involved in choline sulfate biosynthesis. To further examine the crosstalk between HSA32 and HSP101 of higher and lower plant origins, Arabidopsis hsa32-1 knockout mutant was complemented with HSA32 from higher and lower plants. The results showed that only higher plant HSA32 rescued the defect of hsa32-1 under heat stress by retarding the degradation of HSP101. Taken together, the results suggest that higher and lower plant HSA32s have distinct molecular functions, probably by synthesizing different sulfur-containing compounds.
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