2.8. Transcriptomic analysis

The collected algal cells were immediately frozen using liquid nitrogen. Transcriptome (mRNA) was analyzed as previously described [28]. Briefly, total RNA was isolated using TRIzol reagent (Invitrogen, USA) and the genomic DNA was removed using DNase I (TaKara, Japan). Then the quality of mRNA samples was determined using a bioanalyzer (Agilent 2100, Agilent, USA). After quantification with an ultra-micro spectrophotometer (ND-2000, NanoDrop Technologies, USA), RNA library was prepared using the TruSeq™ RNA Sample Preparation Kit (Illumina, USA) and sequenced on an Illumina Hiseq X ten sequencer (Illumina, USA). Bioinformatics analysis was performed on the biocloud platform of Shanghai Majorbio Bio-pharm Technology Co., Ltd. (https://cloud.majorbio.com/). Differentially expressed genes (DEGs) are required to satisfy the criteria of |log₂ (fold change)| ≥ 1 and P < 0.05. KEGG (http://www.genome.jp/kegg/) was used for gene functional analysis. A KEGG pathway was considered as significant if the P-value was ≤0.05. The expression of 14 DEGs was validated by real-time polymerase chain reaction (RT-PCR), and the primers are shown in Table S4.