Cold Acclimation of the Thermoacidophilic Red Alga Galdieria sulphuraria: Changes in Gene Expression and Involvement of Horizontally Acquired Genes

Plant Cell Physiol. 2019 Mar 1;60(3):702-712. doi: 10.1093/pcp/pcy240.


Galdieria sulphuraria is a unicellular red alga that lives in hot, acidic, toxic metal-rich, volcanic environments, where few other organisms survive. Its genome harbors up to 5% of genes that were most likely acquired through horizontal gene transfer. These genes probably contributed to G.sulphuraria's adaptation to its extreme habitats, resulting in today's polyextremophilic traits. Here, we applied RNA-sequencing to obtain insights into the acclimation of a thermophilic organism towards temperatures below its growth optimum and to study how horizontally acquired genes contribute to cold acclimation. A decrease in growth temperature from 42�C/46�C to 28�C resulted in an upregulation of ribosome biosynthesis, while excreted proteins, probably components of the cell wall, were downregulated. Photosynthesis was suppressed at cold temperatures, and transcript abundances indicated that C-metabolism switched from gluconeogenesis to glycogen degradation. Folate cycle and S-adenosylmethionine cycle (one-carbon metabolism) were transcriptionally upregulated, probably to drive the biosynthesis of betaine. All these cold-induced changes in gene expression were reversible upon return to optimal growth temperature. Numerous genes acquired by horizontal gene transfer displayed temperature-dependent expression changes, indicating that these genes contributed to adaptive evolution in G.sulphuraria.

Keywords: Galdieria sulphuraria; Cold stress; Horizontal gene transfer; RNA-Seq; Systems biology; Thermoacidophilic red alga.

MeSH terms

  • Adaptation, Physiological / genetics
  • Adaptation, Physiological / physiology
  • Algal Proteins / genetics
  • Algal Proteins / metabolism
  • Cold Temperature
  • Cold-Shock Response / genetics
  • Cold-Shock Response / physiology
  • Gene Transfer, Horizontal / genetics
  • Gene Transfer, Horizontal / physiology
  • Phylogeny
  • Rhodophyta / genetics
  • Rhodophyta / metabolism*
  • Rhodophyta / physiology
  • Systems Biology / methods


  • Algal Proteins