Identification and Characterization of the Na+/H+ Antiporter NhaS3 from the Thylakoid Membrane of Synechocystis sp. PCC 6803

Abstract

Na؉ /H ؉ antiporters influence proton or sodium motive force across the membrane. Synechocystis sp. PCC 6803 has six genes encoding Na ؉ /H؉ antiporters, nhaS1-5 and sll0556. In this study, the function of NhaS3 was examined. NhaS3 was essential for growth of Synechocystis, and loss of nhaS3 was not complemented by expression of the Escherichia coli Na ؉ /H ؉ antiporter NhaA. Membrane fractionation followed by immunoblotting as well as immunogold labeling revealed that NhaS3 was localized in the thylakoid membrane of Synechocystis. NhaS3 was shown to be functional over a pH range from pH 6.5 to 9.0 when expressed in E. coli. A reduction in the copy number of nhaS3 in the Synechocystis genome rendered the cells more sensitive to high Na ؉ concentrations. NhaS3 had no K ؉ /H ؉ exchange activity itself but enhanced K ؉ uptake from the medium when expressed in an E. coli potassium uptake mutant. Expression of nhaS3 increased after shifting from low CO 2 to high CO 2 conditions. Expression of nhaS3 was also found to be controlled by the circadian rhythm. Gene expression peaked at the beginning of subjective night. This coincided with the time of the lowest rate of CO 2 consumption caused by the ceasing of O 2 -evolving photosynthesis. This is the first report of a Na

Pollen Tubes Lacking a Pair of K+ Transporters Fail to Target Ovules inArabidopsis

“…We used E. coli as a heterologous expression system, as CHX23 failed to rescue growth of alkalinesensitive KTA40-2 yeast mutants. Interestingly, transporters associated with endomembranes in plant cells can be functionally expressed on the PM of E. coli (Uozumi, 2001;Tsunekawa et al, 2009;S. Chanroj and H. Sze, unpublished data).…”

Aquaporin AqpZ Is Involved in Cell Volume Regulation and Sensitivity to Osmotic Stress in Synechocystis sp. Strain PCC 6803

“…1 and Table 1). Interestingly, the peak of the expression of aqpZ corresponded to early subjective night, which is similar to the circadian profile of the Na ϩ /H ϩ antiport system NhaS3 in Synechocystis, which is known to be involved in osmoregulation (48).…”

“…This difference may be the result of the Na ϩ adaptive system in Synechocystis. It has been reported that Synechocystis regulates Na ϩ influx and efflux across the plasma membrane and the thylakoid membrane via an Na ϩ transport system, e.g., an Na ϩ /H ϩ antiporter, in order to control ion homeostasis in the cytosol (11,21,33,48). In addition to the Na ϩ cycling system, NaCl also induces synthesis of the osmolyte glucosylglycerol in Synechocystis (27).…”

“…Sodium is an essential element for cell division, photosynthesis, and pH regulation in cyanobacteria (34,55), although excess amounts of sodium function as the causative element in salinity stress. Synechocystis contains several genes encoding Na ϩ /H ϩ antiporters that mediate the exchange of Na ϩ and H ϩ across the plasma membrane and the thylakoid membrane (14,21,33,48). The potassium transport system also contributes to maintaining the balance of Na ϩ /K ϩ in the cell, which protects it from high-salinity stress and high osmolarity (8,28).…”

Comparative Analysis of kdp and ktr Mutants Reveals Distinct Roles of the Potassium Transporters in the Model Cyanobacterium Synechocystis sp. Strain PCC 6803

“…2G and Table 1). The full recovery of volume probably needs the synthesis and accumulation of the compatible solute glucosylglycerol in the second or later phase of osmoacclimation, which in- (57), nhaS3 (Na ϩ /H ϩ antiporter) (56), and mscL (mechanosensitive channel large conductance) (58) are also indicated (filled circles). duced more water influx and recovery of cell volume (4,5).…”