Transcriptomic analysis reveals the role of MAPK signaling pathway in IgM+ B cells against Pseudomonas plecoglossicida infection in large yellow croaker (Larimichthys crocea)

The large yellow croaker (Larimichthys crocea), an economically important marine fish in China, often suffers serious losses due to visceral white nodule disease caused by Pseudomonas plecoglossicida infection. IgM⁺ B cells play critical roles in the defense against bacterial infection, yet their immune response and underlying mechanisms against the P. plecoglossicida infection in large yellow croaker remain poorly characterized. In this study, we used fluorescence-activated cell sorting (FACS) and RNA sequencing to profile the transcriptomes of head kidney IgM⁺ B cells at different time points after P. plecoglossicida infection. The results showed that P. plecoglossicida infection induced time-dependent transcriptomic changes in IgM⁺ B cells. Mfuzz analysis categorized genes into 9 different clusters based on their expression patterns. Notably, cluster 9, 8 and 1 exhibited specific upregulation at 1, 3, and 7 days post infection (dpi), respectively, while cluster 2 displayed a sustained upregulation pattern throughout infection. KEGG enrichment analysis revealed enhanced energy metabolism and proliferation ability of IgM⁺ B cells after infection. Furthermore, we found that the MAPK signaling pathway was rapidly activated after infection (enriched in cluster 9). qPCR results further confirmed the upregulation of MAPK signaling related genes (cacna1g, map2k1, map3k4, map3k10) at 1 dpi, suggesting its role in regulating the early immune response of B cells. Together, this study comprehensively analyzed the transcriptomic dynamics of IgM⁺ B cells after P. plecoglossicida infection, which would provide insights into the understanding of teleost B cell immunity and offer potential strategies for bacterial disease control in large yellow croaker aquaculture.