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As an important pathogen in aquaculture, Pseudomonas plecoglossicida has caused heavy losses. The expression of an ABC transporter gene- L321_23611 of P. plecoglossicida at 18 °C was found significant higher than those at 28 °C by RNA-seq and qRT-PCR. RNAi significantly reduced the content of L321_ 23611 mRNA in P. plecoglossicida with a maximal decrease of 89.2%. Compared with the wild type strain, the infection of L321_23611- RNAi strain resulted in the reduction in mortality and the onset time delay of a kind of marine teleosts, Epinephelus coioides. The results of dual RNA-seq showed that the RNAi of L321_23611 resulted in a significant change in both pathogen and host transcriptome in the spleens of infected E. coioides. The result of GO and KEGG analysis from dual RNA-seq data showed both host genes of chemokine signaling pathway, coagulation and complement system, hematopoietic cell lineage pathway as well as hemoglobin complex GO term and pathogenic genes of bacterial-type flagellum-dependent cell mortality GO term and flagellar assembly, biosynthesis of amino acids and lysine biosynthesis systems pathways were mainly affected by L321_23611 gene of P. plecoglossicida. The results indicated that: 1. ABC transporter gene- L321_23611 was a virulent gene of P. plecoglossicida. 2. Both the activation of the host immune pathways and depression of pathogenic virulence-related pathways facilitated E. coioides to remove L321_23611 -RNAi strain than the wild type strain of P. plecoglossicida. • RNAi significantly reduced the content of L321_ 23611 mRNA of P. plecoglossicida. • RNAi of L321_23611 reduced the pathogenicity of P. plecoglossicida to E. coioides. • RNAi of L321_23611 significantly up-regulated host immune pathways. • RNAi of L321_23611 down-regulated some pathogenic genes of P. plecoglossicida. [ABSTRACT FROM AUTHOR]

As an important pathogen in aquaculture, Pseudomonas plecoglossicida has caused heavy losses. It was determined with RNA-seq that the expression of a LysR-type transcriptional regulator gene (L321_20267) of P. plecoglossicida at 18 °C was significantly higher than that at 28 °C, which was verified by quantitative real-time PCR (qRT-PCR). RNAi significantly reduced the content of L321_ 20267 mRNA in P. plecoglossicida , with a maximal decrease of 90.63%. Compared with the wild-type strain, infection with the L321_20267- RNAi strain resulted in a 50% reduction in mortality and an onset time delay of Epinephelus coioides , as well as alleviation of the symptoms in E. coioides spleens. Compared with the wild-type strain of P. plecoglossicida , the L321_20267- RNAi strain resulted in a significant change in the spleen transcriptome of infected E. coioides. The results of GO and KEGG analysis showed that genes of serine hydrolase activity, the antigen processing and presentation pathway, the B cell receptor signalling pathway and the chemokine signalling pathway were most affected by the L321_20267 gene of P. plecoglossicida. Meanwhile, the immune genes were related to different numbers of miRNAs and lncRNAs, and some miRNAs were related to more than one gene. The results indicated that 1. L321_20267 is a virulence gene of P. plecoglossicida ; 2. the upregulation of the immune pathways facilitated E. coioides to remove the L321_20267 -RNAi strain compared with the wild-type strain of P. plecoglossicida ; and 3. the immune genes were regulated by miRNA and lncRNA in a complex manner. • The content of L321_ 20267 mRNA of P. plecoglossicida was significantly reduced by RNAi. • The pathogenicity of P. plecoglossicida to E. coioides was significantly reduced by RNAi of the L321_20267 gene. • RNAi of the L321_20267 gene significantly upregulated immune pathways in E. coioides infected with P. plecoglossicida. • The expression of immune genes was regulated by miRNA and lncRNA in a sophisticated manner. [ABSTRACT FROM AUTHOR]