Transcriptomes of Arctic and temperate diatoms
To determine single-nucleotide polymorphisms, transcriptomic profiles were assed for the Arctic diatoms Thalassiosira gravida (5 strains), Chaetoceros diadema, Pseudo-Nitzschia turgidula, Shionodiscus bioculatus, and the temperate diatom Thalassiosira rotula (4 strains) under controlled laboratory conditions. Cultures were maintained at a light intensity of 30µmol photons m^-2 s^-1 with photoperiod of 16:8h at a temperature of 4° and 15°C for Arctic and temperate diatoms, respectively. During the illumination period, 40 ml culture of each strain was filtered using a 10 µm nylon filter (Merck Millipore, USA). The filter was then fixed in 1 ml TriReagent (Sigma-Aldrich, St. Louis, USA) with glass beads and immediately frozen at -80°C for future processing. Cultures were harvested during the mid-exponential growth phase at 4°C for Arctic strains and 15°C for temperate strains. RNA isolation was performed following the detailed protocol by Wohlrab et al. 2017(DOI: 10.1186/s12898-017-0119-y). Library preparation was subsequently carried out using the Illumina Stranded mRNA Prep Ligation Kit (Illumina, San Diego, USA) according to the manufacturer's instructions. The resulting paired-end cDNA libraries were sequenced on a NextSeq 2000 (Illumina, San Diego, USA) using the P3 Reagents kit (2 x 150 cycles).