Project description:By applying Illumina Novaseq 6000, Chlorella sp. TLD6B cells of the control group on day zero and 18, as well as under low salt stress (NaCl1) and under high salt stress (NaCl2) on day 18 were selected for transcriptome sequencing analysis. Meanwhile, 0.05 g/mL ( PEG1) and 0.1 g/mL PEG-6000 (medium for drought stress, PEG2 ) were used to prepare the drought-stressed Chlorella sp. TLD6B cells. Each treatment had two replicates. Clean data were filtered after the removal of adapters, poly-N strands, and low-quality reads. There were no reference genomes for Chlorella sp. TLD6B, and de novo assembly for clean reads was performed by using Trinity. The sequences were compared with databases such as NR, NT, Swiss-Pro, GO, KEGG, PFAM, and KOG using Blast X (e-value ≤ 10-5). The GO annotation of unigenes was obtained using BLAST2GO. FPKM method was used for the analysis of gene expression levels (Trapnell et al., 2010). Out of six samples, a total of 963,078,184 raw reads were generated. A total of 947,225,244 clean reads were obtained based on the base quality score and read length. Meanwhile, the GC percentage in clean reads reached nearly 66.0%, with Q20 being above 96%. A total of 219,577 transcripts with an average length of 1,394 bp were obtained. In total, 155,503 non-redundant unigenes were assembled for the following analyses. The length of the unigenes ranged from 200 bp to 23,825 bp, with an average length of 1,842 bp. Under different salt stress, verification had been conducted with qRT-PCR on nine unigenes of different pathways, which were related to lipid metabolism. The detection results by qRT-PCR were highly correlated with RNA-Seq results (r = 0.890, r2 = 0.791), which indicated that the RNA-Seq data of Chlorella sp. TLD6B under salt stress were accurate and reliable. Our study represents the first detailed analysis of Chlorella sp. TLD6B under salt stress transcriptomes. Hierarchical clustering of differentially expressed genes uncovered several currently uncharacterized genes that may contribute to the function about lipid accumulation of Chlorella sp. TLD6B under salt stress.
