| Summary: | The green microalga genus <i>Dunaliella</i> is mostly comprised of species that exhibit a wide range of salinity tolerance, including inhabitants of hyperhaline reservoirs. Na<sup>+</sup> content in <i>Dunaliella</i> cells inhabiting saline environments is maintained at a fairly low level, comparable to that in the cells of freshwater organisms. However, despite a long history of studying the physiological and molecular mechanisms that ensure the ability of halotolerant <i>Dunaliella</i> species to survive at high concentrations of NaCl, the question of how <i>Dunaliella</i> cells remove excess Na<sup>+</sup> ions entering from the environment is still debatable. For thermodynamic reasons it should be a primary active mechanism; for example, via a Na<sup>+</sup>-transporting ATPase, but the molecular identification of Na<sup>+</sup>-transporting mechanism in <i>Dunaliella</i> has not yet been carried out. Formerly, in the euryhaline alga <i>D. maritima</i>, we functionally identified Na<sup>+</sup>-transporting P-type ATPase in experiments with plasma membrane (PM) vesicles which were isolated from this alga. Here we describe the cloning of two putative P-type ATPases from <i>D. maritima</i>, <i>Dm</i>HA1 and <i>Dm</i>HA2. Phylogenetic analysis showed that both ATPases belong to the clade of proton P-type ATPases, but the similarity between <i>Dm</i>HA1 and <i>Dm</i>HA2 is not high. The expression of <i>Dm</i>HA1 and <i>Dm</i>HA2 in <i>D. maritima</i> cells under hyperosmotic salt shock was studied by qRT-PCR. Expression of <i>DmHA1</i> gene decreases and remains at a relatively low level during the response of <i>D. maritima</i> cells to hyperosmotic salt shock. In contrast, expression of <i>DmHA2</i> increases under hyperosmotic salt shock. This indicates that <i>Dm</i>HA2 is important for overcoming hyperosmotic salt stress by the algal cells and as an ATPase it is likely directly involved in transport of Na<sup>+</sup> ions. We assume that it is the <i>Dm</i>HA2 ATPase that represents the Na<sup>+</sup>-transporting ATPase.
|
|---|