Transcriptomic profiles of Dunaliella salina in response to hypersaline stress

Abstract

Background: Dunaliella salina is a good model organism for studying salt stress. In order to have a global understanding of the expression profiles of Dunaliella salina in response to hypersaline stress, we performed quantitative transcriptomic analysis of Dunaliella salina under hypersaline stress (2.5 M NaCl) of different time duration by the second and third generation sequencing method. Results: Functional enrichment of the up-regulated genes was used to analyze the expression profiles. The enrichment of photosynthesis was observed, accompanied by enrichments of carbon fixation, pigment biosynthetic process and heme biosynthetic process, which also imply the enhancement of photosynthesis. Genes responsible for starch hydrolysis and glycerol synthesis were significantly up-regulated. The enrichment of biosynthesis of unsaturated fatty acids implies the plasma membrane undergoes changes in desaturation pattern. The enrichment of endocytosis implies the degradation of plasma membrane and might help the synthesis of new glycerophospholipid with unsaturated fatty acids. Co-enrichments of protein synthesis and degradation imply a higher protein turnover rate. The enrichments of spliceosome and protein processing in endoplasmic reticulum imply the enhancement of regulations at post-transcriptional and post-translational level. No up-regulation of any Na + or Cl − channels or transporters was detected, which implies that the extra exclusion of the ions by membrane transporters is possibly not needed. Voltage gated Na + and Cl − channels, mechanosensitive ion channel are possible signal receptors of salt stress, and Ca 2+ and MAP kinase pathways might play a role in signal transduction. Conclusion: At global transcriptomic level, the response of Dunaliella salina to hypersaline stress is a systematic work, possibly involving enhancements of photosynthesis, carbon fixation, and heme biosynthetic process, acceleration of protein turnover, spliceosome, protein processing in endoplasmic reticulum, and endocytosis, as well as degradation of starch, synthesis of glycerol, membrane lipid desaturation. Altogether, the changes of these biological processes occurred at trancriptomic level will help understand how a new intracellular balance achieved in Dunaliella salina to adapt to hypersaline environment, which are worth being confirmed at the physiological levels.

Two splice variants of the DsMEK1 mitogen-activated protein kinase kinase (MAPKK) are involved in salt stress regulation in Dunaliella salina in different ways

“…Taken together, the results of this study indicate that AS forms have regulatory functions and may diversify the functions of the DsMEK1 gene in D. salina. [41,42]. For transformation and selection experiments solid and liquid De Walne's medium were employed, and adjusted to contain a final concentration of 0.5 M NaCl.…”

“…D. salina CCAP (1952-5) was provided by the Freshwater Algae Culture Collection of the Institute of Hydrobiology, Wuhan, China. The culture was maintained in De Walne’s medium and cultivated at 25 °C and 40 μmol m −2 s −1 provided by cool-white fluorescent lamps, under a 16/8 h light/dark cycle with various NaCl concentrations (1.5 M and 3.5 M) and 0.4 mM H 2 O 2 [ 41 , 42 ]. For transformation and selection experiments solid and liquid De Walne’s medium were employed, and adjusted to contain a final concentration of 0.5 M NaCl.…”

Weighted gene co-expression network analysis of the salt-responsive transcriptomes reveals novel hub genes in green halophytic microalgae Dunaliella salina

“…It is apparent that several pathways and processes with connection to different mechanisms are contributed to salt stress responses of D. salina . Previously transcriptome analysis, which solely has been focused on DEGs identification showed that “post-translational modifications”, “signal transduction mechanisms”; “translation, ribosomal structure, and biogenesis”; and “RNA processing and modification” similarly enriched in both types of analyses 6 , 25 . Although, systems biology approach applied here rediscovered these processes as responsive mechanisms; however, our analysis showed that some processes such as “sulfur-based metabolisms” and “Proteasome” distinctively enriched in non-preserved modules.…”

“…Expressed sequence tag (EST) profiling of D. salina in hypersaline condition also identified 1401 unique responsive transcripts were contributed in protein synthesis, energy, primary metabolism, and protein fate 5 . Moreover, a recent global transcriptome sequencing showed that enhancements of photosynthesis and biosynthesis of porphyrins, as well as degradation of starch, synthesis of glycerol, membrane lipid desaturation, are taken part in D.salina responses to hypersaline conditions 6 . Hovewer, due to the complexity of salt stresses responding processes in microalgae, underlying molecular mechanisms for salt stress response in microalgae remain a daunting challenge 7 .…”

Two splice variants of the DsMEK1 mitogen-activated protein kinase kinase (MAPKK) are involved in salt stress regulation in Dunaliella salina in different ways

“…Unialgal strains, culture conditions and growth patterns D. salina CCAP (1952-5) was provided by the Freshwater Algae Culture Collection of the Institute of Hydrobiology, Wuhan, China. The culture was maintained in De Walne's medium and cultivated at 25 C and 40 μmol m −2 s −1 provided by cool-white fluorescent lamps, under a 16/8 h light/dark cycle with various NaCl concentrations (1.5 M and 3.5 M) and 0.4 mM H 2 O 2[41,42]. For transformation and selection experiments solid and liquid De Walne's medium were employed, and adjusted to contain a final concentration of 0.5 M NaCl.…”