Identification of temperature stress responsive genes in greater amberjack（Seriola dumerili） by transcriptome analysis

【Objective】 The aim of this study was to identify genes related to temperature stress response in greater amberjack（Seriola dumerili） based on transcriptome sequencing, which could provide theoretical reference for exploring the mechanism of high temperature tolerance of Seriola dumerili and molecular mechanism of response to high temperature stress. 【Method】 Seriola dumerili were selected as the research objects and divided into 25 ℃ （T25）, 28 ℃ （T28）, 31 ℃ （T31） and 34 ℃ （T34） groups according to the temperature setting. The Seriola dumerili juveniles in each group were raised under the corresponding temperature conditions for 7 d. On the 7^th day of the experiment, 6 Seriola dumerili juveniles were randomly selected from each group and intestinal tissues were collected. Total RNA from intestinal tissues was extracted using TRIzol reagent, cDNA library was constructed and transcriptome sequencing was performed using the Illumina NovaSeq 6000 platform. Differentially expressed genes（DEGs） were screened using DESeq2, and GO functional annotation and KEGG signaling pathway enrichment analysis were performed. Real-time fluorescence quantitative PCR was used to detect the relative expression levels of DEGs to verify the transcriptome results. 【Result】 All the juveniles of Seriola dumerili in the T34 group died on the first day of feeding, indicating that they had a severe high temperature stress response under this temperature. Transcriptome sequencing analysis showed that 5864.48, 6506.81 and 5952.27 Mb high-quality bases and 39.40×10⁶, 43.67×10⁶ and 39.93×10⁶ high-quality sequences were obtained in the T25, T28 and T31 groups respectively. The average mapping rates of genes mapped to the genome of Seriola dumerili were 95.85%, 95.80% and 95.79% respectively. DEGs screening results showed that a total of 2043 DEGs were obtained in the T25 vs T28 group and a total of 1218 DEGs were obtained in the T25 vs T31 group. Twelve and seven heat shock protein related DEGs were obtained in the T25 vs T28 and T25 vs T31 groups respectively, and ten and six DEGs were significantly up-regulated respectively（P＜0.05）. In addition, DEGs related to immune function and stress function were screened. GO functional annotation and enrichment analysis results showed that the DEGs in T25 vs T28 and T25 vs T31 groups were annotated to 3 functional categories:molecular function, cellular component and biological process. The DEGs in T25 vs T28 group were annotated to GO functional items such as small molecule metabolic process, organic acid metabolic process and small molecule biosynthesis process, and the DEGs in T25 vs T31 group were mainly annotated to GO functional items such as small molecule metabolic process, organic acid metabolic process and oxygen-containing acid metabolic process. KEGG signaling pathway enrichment analysis results showed that the DEGs in T25 vs T28 group were mainly enriched in signaling pathways such as proteasome, cysteine and methionine metabolism, and the DEGs in T25 vs T31 group were mainly enriched in signaling pathways such as endoplasmic reticulum protein processing, serine and threonine metabolism. Real-time fluorescence quantitative PCR detection verification results showed that the relative expression change trend of the 7 DEGs selected in T25 vs T28 and T25 vs T31 groups was basically consistent with the fragments per kilobase of exon model per million mapped fragments（FPKM） variation trend in transcriptome, indicating that the transcriptome data were reliable. 【Conclusion】 Under high temperature stress, Seriola dumerili effectively maintains cellular protein homeostasis and redox balance by activating a molecular chaperone system centered on heat shock proteins and synergistically regulating the innate immune recognition signaling pathway and endoplasmic reticulum stress response. Seriola dumerili may have an adaptive mechanism to respond to temperature stress through a stress proteinimmune recognition-endoplasmic reticulum repair synergistic network.