Transcriptomic and metabolomic insights into the role of the <i>flgK</i> gene in the pathogenicity of <i>Pseudomonas plecoglossicida</i> to orange-spotted grouper (<i>Epinephelus coioides</i>)
Biao Yuan, 集美大学水产学院, 福建 厦门 361021, 中国, Lingmin Zhao, Zhixia Zhuang, Xiaoru Wang, Qi Fu, Huabin Huang, Lixing Huang, Yingxue Qin, Qingpi Yan, 厦门华厦学院环境与公共健康学院, 福建 厦门 361024, 中国
Abstract
<i>Pseudomonas plecoglossicida</i> is the pathogen responsible for visceral white spot disease in large yellow croaker (<i>Larimichthys crocea</i>) and orange-spotted grouper (<i>Epinephelus coioides</i>). Previously, RNA sequencing showed that <i>P. plecoglossicida</i> <i>flgK</i> gene expression was significantly up-regulated in orange-spotted grouper spleens during infection. To explore the role of <i>flgK</i> in <i>P. plecoglossicida</i> pathogenicity, RNA interference (RNAi) was performed to silence the <i>P. plecoglossicida</i> <i>flgK</i> gene, and the mutant (<i>flgK</i>-RNAi strain) with the best silencing efficiency (89.40%) was chosen for further study. Results showed that <i>flgK</i> gene silencing significantly attenuated <i>P. plecoglossicida</i> motility, adhesion, and biofilm formation. Compared to those fish infected with the wild-type strain of <i>P. plecoglossicida</i>, orange-spotted grouper infected with the <i>flgK</i>-RNAi strain showed a 55% increase in the survival rate and a one-day delay in time of first death, with fewer pathogens in the spleen and fewer white spots on the spleen surface. RNAi of <i>flgK</i> significantly affected the transcriptome and metabolome of the spleen in infected orange-spotted grouper. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the C-type lectin receptor signaling pathway was the most significantly changed immune-related pathway and the mitogen-activated protein kinase (MAPK) signaling pathway was related to multiple immune-related pathways. Furthermore, arginine biosynthesis and glycerophospholipid metabolism were the most significantly changed metabolism-related pathways. These findings suggest that<i> flgK</i> is a virulence gene of <i>P. plecoglossicida</i>. Furthermore, <i>flgK</i> appears to be involved in the regulation of motility, adhesion, and biofilm formation in <i>P. plecoglossicida</i>, as well as in the regulation of inflammatory and immune responses of orange-spotted grouper to <i>P. plecoglossicida</i> infection.