EXPRESSION OF A GENE ENCODING A 16.9-KDA HEAT-SHOCK-PROTEIN, OSHSP16.9, IN ESCHERICHIA-COLI ENHANCES THERMOTOLERANCE

A gene encoding the rice 16.9-kDa class I low-molecular-mass (LMM) hea t-shock protein (HSP), Oshsp16.9, was introduced into Escherichia coli using the pGEX-2T expression vector to analyze the possible function of this LMM HSP under heat stress, It is known that E. coli does not n ormally produce class I LMM HSPs. We compared the survivability of E, coli XL1-Blue cells transformed with a recombinant plasmid containing a glutathione S-transferase (GST)-Oshsp16.9 fusion protein (pGST-FL ce lls) with the control E. coli cells transformed with the pGEX-2T vecto r (pGST cells) under heat-shock (HS) after isopropyl beta-D-thiogalact opyranoside induction. The pGST-FL cells demonstrated thermotolerance at 47.5 degrees C, a treatment that was lethal to the pGST cells, When the cell lysates from these two E. coli transformants were heated at 55 degrees C, the amount of protein denatured in the pGST FL cells was 50% less than that of the pGST cells, Similar results as pGST-FL cell s were obtained in pGST-N78 cells (cells produced a fusion protein wit h only the N-terminal 78 aa in the Oshsp16.9 portion) but not in pGST- C108 cells (cells produced a fusion protein with C-terminal 108 aa in the Oshsp16.9 portion), The acquired thermotolerant pGST-FL cells synt hesized three types of HSPs, including the 76-, 73-, and 64-kDa protei ns according to their abundance at a lethal temperature of 47.5 degree s C, This finding indicates that a plant class I LMM HSP, when effecti vely expressed in transformed prokaryotic cells that do not normally s ynthesize this class of LMM HSPs, may directly or indirectly increase thermotolerance.