Transcriptomic insights into immune responses to ulcerative syndrome in Pseudobagrus ussuriensis

Though ulcerative syndrome is the dominant disease in aquaculture of the Ussuri catfish (Pseudobagrus ussuriensis), available information for the disease in this fish is seriously limited. In the present study, the pathogen of ulcerative syndrome in P. ussuriensis was isolated and identified as Aeromonas veronii for the first time. To gain insight into the immune response against ulcerative syndrome, comparative transcriptome analyses of the liver, head kidney and spleen were performed between infected and healthy P. ussuriensis. A total of 73,772 unigenes with a mean length of 1172 bp were generated, and 44,996 (60.99%) were successfully annotated in public databases. Differentially expressed genes (DEGs) between infected and control groups were detected: 413 were identified in the liver (224 up-regulated and 189 down-regulated), 691 in the head kidney (225 up-regulated and 466 down-regulated), and 445 in the spleen (262 up-regulated and 183 down-regulated). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that DEGs were classified into 17 GO categories and 40 immune-related KEGG pathways in the liver, 36 GO categories and 45 immune-related pathways in the head kidney, and 39 categories and 38 immune-related pathways in the spleen. Through GO and KEGG annotation, 237 immune-related DEGs (115 up-regulated and 122 down-regulated) involving 212 annotated genes were identified. The DEGs reflected both innate and adaptive immunity responses against ulcerative syndrome. Twenty-six selected DEGs were successfully validated through real-time quantitative PCR. The results of this study provide basic information on immune responses of the liver, head kidney and spleen during ulcerative syndrome. This information will be useful for future genetic studies on the molecular mechanisms of the immune system and helpful for genetic improvement of P. ussuriensis against ulcerative syndrome.

Automated summary

This study identified Aeromonas veronii as the pathogen causing ulcerative syndrome in Pseudobagrus ussuriensis for the first time, and revealed differential gene expressions in the liver, head kidney, and spleen of infected fish. The immune-related DEGs involved in both innate and adaptive immunity responses against ulcerative syndrome were identified, providing valuable information for future genetic studies and genetic improvement of P. ussuriensis against ulcerative syndrome.