Expression analysis of the low-molecular-mass heat-shock gene in rice, Oshsp18.0-II, under abiotic stresses and the protective function in Escherichia coli conferred by recombinant Oshsp18.0-II protein

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All plants synthesize multiple families of low-molecular-mass heat shock proteins (LMM HSPs). Plant LMM HSPs have been grouped to six classes based on sequence homology, immunological crossreactivity, and localization in different cellular compartments. In which, the class I and class II LMM HSPs are localized in the cytoplasm of plant cells. Accumulating evidences support the function of LMM HSPs in resistance to high temperature stress in plants. A cDNA clone, Oshsp18.0-II, encoding a 18.0 kDa class II LMM HSP was isolated from rice previously (Chang, P.-F. L. et al., unpublished results). To gain an insight into its regulation by environmental stimuli, the expression profiles of Oshsp18.0-II under diverse stresses, including heat (41℃), cold (4℃), salt (0.3 M NaCl) and drought (dehydrated the root in air), were analyzed. The results presented in this study clearly demonstrate that Oshsp18.0-II is transcriptionally regulated by heat stress, but not by other stress treated. During a time course of 24 h, the maximum level of Oshsp18.0-II mRNA was found at 1 h of heat treatment. The function of the rice class II LMM HSP was studies by overproduction of the Oshsp18.0-II fusion protein in transformed E. coli cells. The results suggest that the heterologous expression of the Oshsp18.0-II fusion protein increases the thermotolerance of E. coli cells in vivo and provided thermoprotection to E. coli soluble proteins in vitro. Overproduction of the Oshsp18.0-II fusion protein in E. coli also confers tolerance of E. coli cells to UV irradiation.