Comparative Transcriptomics of Wild-Type and LAAO-Knockout Zebrafish Challenged with Streptococcus agalactiae

L-amino acid oxidase (LAAO) has been found to play an important role in fish immune function in recent years. It has been reported to have broad-spectrum antibacterial, anti-parasitic and other immune activities. Our previous study found that LAAO had significant killing activity against Streptococcus agalactiae in vitro. This study investigated the in vivo regulatory mechanism of LAAO in the S.agalactiae infection process in teleost fish. A zebrafish model with LAAO gene knockout was generated by CRISPR/Cas9 technology. Transcriptome analysis was performed on the liver and gill tissues of LAAO(-/-) and wild-type zebrafish under normal conditions and 12 h after challenge with 2 × 10⁷ CFU/mL S.agalactiae. The results showed that the ability of zebrafish to resist S.agalactiae infection was significantly reduced after LAAO gene knockout. In the liver of LAAO(-/-) and wild-type zebrafish, the most highly up-regulated genes were chia.3, chia.1, chia.2 and ctrl; the most down-regulated genes were vtg4, vtg7 and vtg6. In gill, ptpra, nono and ptx3a were the most up-regulated genes, scpp5 and slc24a2 were the most down-regulated genes. The most up-regulated and down-regulated genes in the liver and gill after challenge were ctsba and mhc1uba. Regardless of infection status, both tissues showed enrichment in amino acid metabolism and synthesis-related pathways, carbohydrate metabolism-related pathways, and lipid-related pathways. Differentially expressed genes (DEGs) associated with immune pathways were enriched in the PPAR signaling pathway, peroxisome pathway and glutathione metabolism pathway. The results of this study provide a reference for the molecular regulation mechanism of LAAO in fish.