The effect of a LysR-type transcriptional regulator gene of Pseudomonas plecoglossicida on the immune responses of Epinephelus coioides

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 degrees C was significantly higher than that at 28 degrees 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.