Synechocystis PCC6803 and PCC6906 dnaK2 expression confers salt and oxidative stress tolerance in Arabidopsis via reduction of hydrogen peroxide accumulation

Abiotic stress slows plant growth and development. Because salt stress, particularly from NaCl, acts as an important limiting factor in agricultural productivity, the identification and manipulation of genes related to salt tolerance could improve crop productivity. Prokaryotic, heat shock protein (Hsp), DnaK from the ubiquitous Hsp70 family is upregulated in cells that are under abiotic stress. Synechocystis spp. cyanobacteria encode at least three potential DnaK proteins in their genome. Here, expressions of dnaK1 s and dnaK2 s from two Synechocystis spp. PCC6803 (Sy6803) and PCC6906 (Sy6906), enhanced salt tolerance in a dnaK -defective Escherichia coli strain. In contrast, dnaK3 s in both strains were ineffective, indicating that dnaK3 is functionally different from dnaK1 and dnaK2 in Synechocystis spp. under salt stress. Ectopic expression of dnaK2 s from Sy6803 and Sy6906 conferred salt tolerance in transgenic Arabidopsis plants, which exhibited greater root length, chlorophyll content, fresh weight, and survival rate than wild type plants, all in the presence of NaCl. In transgenic plants, hydrogen peroxide (H 2 O 2 ) accumulation was reduced under NaCl stress and loss of chlorophyll content was reduced under H 2 O 2 stress. Overall results suggest that dnaK2 s from Sy6803 and Sy6906 confer salt and oxidative tolerance in transgenic plants by reduction of H 2 O 2 accumulation.