De novo transcriptome analysis of an Arctic microalga, Chlamydomonas sp.

Microalgal Chlamydomonas species are abundant in polar regions and provide a novel model system for investigating the physiological characteristics and mechanisms related to multiple stresses. As part of an effort to understand the adaptation mechanism of polar organisms, we analyzed the transcriptome of an arctic microalgal strain, ArF0006, from the KOPRI Culture Collection of Polar Microorganisms (KCCPM). ArF0006 was isolated from ice-covered freshwater from the Arctic and, therefore, showed optimal growth at low temperatures. It was identified as a Chlamydomonas sp. based on morphology; this was confirmed by molecular phylogenetic analysis. A total of 64,712 reads were generated from pyrosequencing and assembled into 45,443 contigs and 19,424 singletons. Contigs ranged from 100-4,673 bp, with an average of 665 bp. Functional annotations of contigs with a high number of reads were related principally to cold response or photosynthesis. Also, several fatty acid and TGA biosynthesis-related genes and putative homologs of antifreeze protein were identified. A comparison of ArF0006 with Chlamydomonas reinhardtii, Ostreococcus tauri, and Arabidopsis thaliana was performed, and RT-PCR analysis verified the effect of growth temperature on gene expression pattern. Therefore, ArF0006 transcriptome analysis provided useful genetic information regarding cold tolerance that could be useful for bioindustrial applications.