Gene expression and metabolic pathways related to cell growth and lipid synthesis in diatom Nitzschia ZJU2 after two rounds of mutagenesis by γ-rays

The transcriptomes of original diatom strain (wild-type, Nitzschia sp.) and a mutant strain (Nitzschia ZJU2), which exhibited rapid growth and high lipid productivity after two rounds of mutagenesis by gamma-rays, were sequenced using the Illumina sequencing platform. Genes in the metabolic pathway and those related to cell growth and lipid synthesis were compared between the two strains. Up to 25 804 and 35 228 transcripts were detected in Nitzschia sp. and Nitzschia ZJU2, respectively. A total of 3939 genes were up-regulated in mutant Nitzschia ZJU2. Nine metabolic pathways involved in cell growth and carbohydrate and protein syntheses obviously changed. Genes involved in lipid synthesis, such as acetyl-CoA carboxylase and diacylgycerol O-acyltransferase, were obviously up-regulated. These phenomena promoted cell growth and lipid synthesis, so as to increase the lipid production of cells. Analysis of single nucleotide polymorphisms revealed the presence of 40 795 nonsynonymous mutations in Nitzschia ZJU2, which indicated that nuclear irradiation triggers algal mutation.