The effects of N,N′-dicyclohexylcarbodiimide (DCCD), non-specific inhibitor of various transport systems functioning in biological membranes, on Na+-transporting P-type ATPase of the green halotolerant microalga Dunaliella maritima were studied in the experiments with vesicular plasma membranes isolated from the alga cells. The effects of DCCD on electrogenic/ion transport function of the enzyme and its ATP hydrolase activity were investigated. Electrogenic/ion transport function of the enzyme was recorded as a Na+-dependent generation of electric potential on the vesicle membranes with the help of the potential-sensitive probe oxonol VI. It was found that unlike many other ion-transporting ATPases, the Na+-ATPase of D. maritima is insensitive to DCCD. This agent did not inhibit either ATP hydrolysis catalyzed by this enzyme or its transport activity. At the same time DCCD affected the ability of the vesicle membranes to maintain electric potential generated by the D. maritima Na+-ATPase. The observed effects can be explained based on the assumption that DCCD interacts with the Na+/H+ antiporter in the plasma membrane of D. maritima.

Partial sequences of P-type ATPases were cloned from the marine microalgae Dunaliella maritima: two presumably H+-ATPases (DmHA1 and DmHA2) and two putative Ca2+-ATPases (DmCA1 and DmCA2). The functions of cloned proteins were estimated on the bases of their primary structure similarity with the proteins whose functions have been already characterized. The transcriptional response of cloned ATPase genes to a sharp increase in the NaCl concentration in the culture medium (from 100 to 500 mM) was investigated by quantitative RT-PCR. Hyperosmotic salt shock led to a significant increase in DmHA2 expression and to a slight increase in DmCA2 expression, while the expression of two other ATPases, DmHA1 and DmCA1, was repressed. The obtained data indicate that DmHA2 is involved in maintenance of ion homeostasis in D. maritima cells under hyperosmotic salt shock.

Министерство науки и высшего образования РФ Российская академия наук Общество физиологов растений России Правительство Республики Татарстан Федеральный исследовательский центр «Казанский научный центр Российской академии наук» Казанский институт биохимии и биофизики ФИЦ КазНЦ РАН Институт физиологии растений им.К.А

De novo assembled transcriptomes of the marine microalga Dunaliella tertiolecta (Chlorophyta) were analyzed. Transcriptome assemblies were performed using short-read RNA-seq data deposited in the SRA database (DNA and RNA Sequence Read Archive, NCBI). A merged transcriptome was assembled using a pooled RNA-seq data set. The goal of the study was in silico identification of nucleotide sequences encoding P-type ATPases in D. tertiolecta transcriptomes. P-type ATPases play a considerable role in the adaptation of an organism to a variable environment, and this problem is particularly significant for microalgae inhabiting an environment with an unstable ionic composition. Particular emphasis was given to searching for a sequence coding Na+-ATPase. This enzyme is expected to function in the plasma membrane of D. tertiolecta like in some marine algae, in particular, in the closely related alga Dunaliella maritima. An ensemble of 12 P-type ATPases consisting of members belonging to the five main subfamilies of the P-type ATPase family was revealed in the assembled transcriptomes. The genes of the following P-type ATPases were found: (1) heavy metal ATPases (subfamily PIB); (2) Ca2+-ATPases of SERCA type (subfamily P2A); (3) H+-ATPases (subfamily P3); (4) phospholipid-transporting ATPases (flippases) (subfamily P4); (5) cation- transporting ATPases of uncertain specificities (subfamily P5). The presence of functional Na+-ATPases in marine algae is presently undoubted. However, contrary to expectations, we failed to find a nucleotide sequence encoding a protein that could unequivocally be considered a Na+-ATPase. Further study is necessary to elucidate the roles of in silico revealed D. tertiolecta ATPases in Na+ transport.

2 Федеральное государственное бюджетное образовательное учреждение высшего образования «Санкт-Петербургский государственный университет», Центр геномной биоинформатики им

Chlorophyll fluorescence induction curves were used as a means to assess the functional condition of the photosynthetic apparatus in cells of the halotolerant green microalga Dunaliella maritima (Massjuk) (division Chlorophyta) exposed to hyperosmotic salt shock of various intensities. The shock was caused by the transfer of algal cells grown in the medium with 0.5 M NaCl to the media with elevated NaCl concentrations (1.0, 1.5, and 2.0 M). Parameters of chlorophyll fluorescence (F 0, F m, F 0′, F t′) were measured by means of a specialized pulse-amplitude-modulation fluorometer PAM 2100. In addition, the rate of photosynthetic oxygen evolution as well as the intracellular Na+ and glycerol content (the main osmolyte in this microalga) were determined. The hyperosmotic salt shock was found to elevate the intracellular Na+ content and reduce the functional activity of PSII in D. maritima. The suppression of PSII activity was evident from the decrease in the maximal quantum yield of photochemical energy conversion in PSII, the decreased rate of linear electron transport, the increased reduction of the primary acceptor QA, and the suppression of photosynthetic O2 evolution. The functional activity of PSII recovered gradually along with restoration of osmotic and ionic balance in algal cells. It is proposed that PSI ensures energy supply during cell responses of D. maritima to hyperosmotic salt shock.