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

Abstract

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 dnaK1s and dnaK2s from two Synechocystis spp. PCC6803 (Sy6803) and PCC6906 (Sy6906), enhanced salt tolerance in a dnaK-defective Escherichia coli strain. In contrast, dnaK3s in both strains were ineffective, indicating that dnaK3 is functionally different from dnaK1 and dnaK2 in Synechocystis spp. under salt stress. Ectopic expression of dnaK2s 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 (H2O2) accumulation was reduced under NaCl stress and loss of chlorophyll content was reduced under H2O2 stress. Overall results suggest that dnaK2s from Sy6803 and Sy6906 confer salt and oxidative tolerance in transgenic plants by reduction of H2O2 accumulation.

The overproduction ofSynechocystissp. PCC 6803 heat-shock protein (Sll0170) protectsEscherichia coliagainst high-temperature stress

“…[21] Effect of recombinant DnaK2 on tolerance to heat-shock and high-temperature stresses in Escherichia coli cells While the exact physiological functions of multiple DnaK proteins in cyanobacteria are still unknown, only DnaK2 and DnaK3 are essential in Synechocystis and Synechococcus. [5,6,22] Accordingly, DnaK2 seems to be the major Hsp70 protein involved in the stress response, [6] whereas DnaK3 has a specialized function, which involves the highly conserved prolonged C-terminus of the protein. [22] In contrast to other bacteria, neither dnaK nor any other heat-shock genes such as grpE and dnaJ are located near the hrcA genes in Synechocystis and other cyanobacteria.…”

“…[3,4] Cyanobacterial genomes typically encode multiple heat-shock protein 70 (Hsp70) (DnaK) chaperones, and in the genome of the cyanobacterium Synechocystis PCC 6803, three DnaK proteins are encoded. [4,5] Proteins of the 70 kDa heat-shock protein family (Hsp70) are ubiquitously distributed in all kingdoms of life, and in eukaryotes members of this family can be found in several organelles as well as in the cytosol. [3,6] The main functions of the proteins are to ensure proper folding of polypeptide chains, to keep proteins in a translocationcompetent state after synthesis, and to prevent misfolding and aggregation of proteins caused by e.g.…”

“…[10] Several studies indicate that DnaK2 is essential for the growth of Synechocystis under normal conditions. [5,6] Therefore, it could be suggested that, among Synechocystis DnaKs, DnaK2 is the most abundant protein and that DnaK2 has some specific functions that cannot be compensated for by the remaining two DnaK proteins. [5,6,11] Transformation of heat-shock genes from Synechocystis sp.…”

“…[5,6] Therefore, it could be suggested that, among Synechocystis DnaKs, DnaK2 is the most abundant protein and that DnaK2 has some specific functions that cannot be compensated for by the remaining two DnaK proteins. [5,6,11] Transformation of heat-shock genes from Synechocystis sp. PCC 6803 into the bacterial host Escherichia coli cells is one of the most fundamental and indispensable techniques for studying gene functions.…”

“…Ever since Mandel and Higa [12] proposed the chemical transformation protocol in 1970, considerable variations in this basic technique have been studied. [5,13,14] The aim of this study was to isolate the Sll0170 gene (DnaK2) from Synechocystis PCC 6803 and validate its functions, using a gain-of-function approach by overproduction of DnaK2 in E. coli. The recombinant E. coli cells showed significant increased resistance to heat-shock and high-temperature stresses.…”