Differential Expression of Stress Adaptation Genes in a Diatom Ulnaria acus under Different Culture Conditions.

Diatoms are a group of unicellular eukaryotes that are essential primary producers in aquatic ecosystems. The dynamic nature of their habitat necessitates a quick and specific response to various stresses. However, the molecular mechanisms of their physiological adaptations are still underexplored. In this work, we study the response of the cosmopolitan freshwater diatom Ulnaria acus (Bacillariophyceae, Fragilariophycidae, Licmophorales, Ulnariaceae, Ulnaria) in relation to a range of stress factors, namely silica deficiency, prolonged cultivation, and interaction with an algicidal bacterium. Fluorescent staining and light microscopy were used to determine the physiological state of cells under these stresses. To explore molecular reactions, we studied the genes involved in the stress response-type III metacaspase (MC), metacaspase-like proteases (MCP), death-specific protein (DSP), delta-1-pyrroline-5-carboxylate dehydrogenase (ALDH12), and glutathione synthetase (GSHS). We have described the structure of these genes, analyzed the predicted amino acid sequences, and measured their expression dynamics in vitro using qRT-PCR. We demonstrated that the expression of UaMC1, UaMC3, and UaDSP increased during the first five days of silicon starvation. On the seventh day, it was replaced with the expression of UaMC2, UaGSHS, and UaALDH. After 45 days of culture, cells stopped growing, and the expression of UaMC1, UaMC2, UaGSHS, and UaDSP increased. Exposure to an algicidal bacterial filtrate induced a higher expression of UaMC1 and UaGSHS. Thus, we can conclude that these proteins are involved in diatoms' adaptions to environmental changes. Further, these data show that the molecular adaptation mechanisms in diatoms depend on the nature and exposure duration of a stress factor.

Effects of GSH1 and GSH2 Gene Mutation on Glutathione Synthetases Activity of Saccharomyces cerevisiae.

In this paper, three mutants from wild Saccharomyces cerevisiae HBU2.558, called U2.558, UN2.558, and UNA2.558, were screened by UV, sodium nitrite, Atmospheric and room temperature plasma, respectively. Glutathione production of the three mutants increased by 41.86, 72.09 and 56.76%, respectively. We detected the activity of glutathione synthetases and found that its activity was improved. Amino acid sequences of three mutant colonies were compared with HBU2.558. Four mutants: Leu51→Pro51 (L51P), Glu62→Val62 (E62V), Ala332→Glu332 (A332E) and Ser653→Gly653 (S653G) were found in the analysis of γ-glutamylcysteine ligase. L51 is located adjacently to the two active sites of GCL/E/Mg2+/ADP complex in the overall GCL structure. L51P mutant spread distortion on the ß-sheet due to the fact that the φ was changed from -50.4° to -40.2°. A mutant Leu54→Pro54 (L54P) was found in the analysis of glutathione synthetase, and L54 was an amino acid located between an α-helix and a ß-sheet. The results confirm that introduction of proline located at the middle of the ß-sheet or at the N- or C-terminal between α-helix and ß-sheet or, i.e., L51P and L54P, changed the φ, rigidity, hydrophobicity and conformational entropy, thus increased protein stability and improved the enzyme activity.