| All organisms respond to temperature stress with production of a defined set of proteins called heat shock protein. The small heat shock proteins (sHSP) are ubiquitous in nature, but unusually abundant and diverse in higher plants as oppose to other eukaryotes. The sHSPs range in size from 17 to 30 kDa and share a conserved C-terminal domain. In higher plants six nuclear gene families encoding sHSPs have been defined. Each gene family encodes proteins founding a distinct cellular compartment, including the cytocol, chloroplast, ER and mitochondrion. Recently, a salient process involved in the production of sHSP induced by heat shock and the relationship between sHSP and thermotolerance was proposed. However, little is known about the production of sHSP induced by chilling stress and relationship between sHSP and chiliing tolerance.The results are as follows:1. The phylogenetic analysis of CaHSP18 with sHSP genes from other plant species indicated that sweet pepper, tobacco and maize share one cluster. The deduced protein sequence exhibits a high degree of conservation in two consensus regions near the carboxyl-terminal end of the protein. 2. Expression of CaHSP18 was obviously induced by high temperature (42℃) in all organs with the highest level in leaves, and no transcript was observed in any of organs at 25℃. But expression of CaHSP18 gene was also detected under low temperature stress.3. Recombinant CaHSP18 was overexpressed in E coli. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of cell lysates suggested that CaHSP18 was expressed in E coli. Growth curves of wild type and transformed cells were similarly at 37℃. Upon transfer from 37℃to 50℃or 4℃those cells that accumulated CaHSP18 showed improved viability compared with control.4. Sense CaHSP18 gene was transformed into tomato plants. PCR, northern and western blot analysis showed that CaHSP18 gene was overexpressed in transgenic tomato plants. At normal temperature, there were no differences between the wild types and transgenic tomato plants. But the transgenic plants kept higher level of O2 evolution and Fv/Fm decreased more during chilling stress than the wild type tomato plants. Overexpression of CaHSP18 gene in transgenic tomato alleviates PSII photoinhibition during chilling stress. These results indicated that the overexpression of the CaHSP18 gene in tomato plants protected the photosynthetic apparatus from both high temperature and chilling stress. |
