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  • Author or Editor: Na-Hyun Song x
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The expression and function of DcHsp17.7, a small heat shock protein expressed in carrot (Daucus carota L.), was examined under oxidative and osmotic stress conditions. Comparative analysis revealed that DcHsp17.7 is a cytosolic Class I protein. Sequence alignment showed that DcHsp17.7 has the characteristic α-crystalline domain-containing consensus regions I and II. Under oxidative [hydrogen peroxide (H2O2)] and osmotic (polyethylene glycol) stress conditions, DcHsp17.7 accumulated in carrot leaf tissue. To examine its function under these abiotic stress conditions, the coding sequence of DcHsp17.7 was introduced into Escherichia coli and expressed by isopropyl β-D-1-thiogalactopyranoside treatment. Under both oxidative and osmotic stress conditions, heterologously expressed DcHsp17.7 enhanced bacterial cell viability. The expression level of soluble proteins was higher in transgenic cells expressing DcHsp17.7 when compared with controls under these stress conditions. These results suggest that DcHsp17.7 confers tolerance to both oxidative and osmotic stresses and thereby functions as a molecular chaperone during the stresses examined.

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The expression profile and functional properties of DcHsp17.7, a small heat shock protein from carrot (Daucus carota L.), were examined under cold stress. Immunoblot analysis showed that low temperature (2 °C) induced DcHsp17.7 in vegetative tissues. Differential accumulation of the transcript and protein under the cold suggests that expression of DcHsp17.7 might be controlled at the transcriptional and/or translational levels. To examine the functional properties of DcHsp17.7, the gene was expressed in Escherichia coli. When exposed to 2 °C for 10 days, transformed cells expressing DcHsp17.7 showed 115% cell viability, whereas control cells recorded 24%, suggesting that DcHsp17.7 can confer cold tolerance. The amount of soluble protein under the cold was 83% in transformed cells expressing DcHsp17.7, whereas the control cells showed only 52%, suggesting that DcHsp17.7 functions as a molecular chaperone preventing cold-induced protein degradation. Native-polyacrylamide analysis revealed that DcHsp17.7 was found in two oligomeric complexes (≈160 and 240 kDa) and possibly multiple complexes (from 300 to 450 kDa) in cold-stressed carrot and transformed E. coli, respectively. During prolonged cold stress, these complexes disappeared and then reappeared, suggesting that the dissociation and reassociation of DcHsp17.7 complexes might be important for the function of the protein.

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