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

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

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Institute of Plant Biochemistry, Cluster of Excellence on Plant Sciences (CEPLAS), Heinrich Heine University, D�sseldorf, Germany.
Department of Plant Biology, Ecology & Evolution, Oklahoma State University, Stillwater, OK, USA.
Graduate School of Semiconductor and Chemical Engineering, Chonbuk National University, Jeonju, South Korea.
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, USA.


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.


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

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