Comparative analysis of thehspAmutant and wild-typeSynechocystissp. strain PCC 6803 under salt stress: evaluation of the role ofhspAin salt-stress management.

DNA microarray analysis has previously revealed thathspA, which encodes a small heat-shock protein, is the second most highly expressed gene under salt stress inSynechocystissp. strain PCC 6803. Consequently, anhspAdeletion mutant was studied under various salt stresses in order to identify a potential role of HspA in salt stress management. The mutant had a growth disadvantage under moderate salt stress. It lost the ability to develop tolerance to a lethal salt treatment by a moderate salt pre-treatment when the tolerance was evaluated by cell survival and the level of major soluble proteins, phycocyanins, while the wild-type acquired tolerance. Under various salt stresses, the mutant failed to undergo the ultrastructural changes characteristic of wild-type cells. The mutant, which showed higher survival than the wild-type after a direct shift to lethal salt conditions, accumulated higher levels ofgroESL1andgroEL2transcripts and the corresponding proteins, GroES, GroEL1, and GroEL2, suggesting a role for these heat-shock proteins in conferring basal salt tolerance. Under salt stress, heat-shock genes, such ashspA,groEL2, anddnaK2, were transcriptionally induced and greatly stabilized, indicating a transcriptional and post-transcriptional mechanism of acclimation to salt stress involving these heat-shock genes. [ABSTRACT FROM AUTHOR]