| Summary: | MicroRNAs (miRNAs) are small RNA molecules that function in the post-transcriptionally regulation of the expression of diverse genes, including those involved in immune defense. <i>Edwardsiella tarda</i> can infect a broad range of hosts and cause severe disease in aquatic species, including Japanese flounder (<i>Paralichthys olivaceus</i>). In this study, we examined the regulation mechanism of a flounder miRNA, pol-miR-155, during the infection of <i>E. tarda</i>. Pol-miR-155 was identified to target flounder ATG3. Overexpression of pol-miR-155 or knockdown of ATG3 expression suppressed autophagy and promoted the intracellular replication of <i>E. tarda</i> in flounder cells. Overexpression of pol-miR-155 activated the NF-κB signaling pathway and further promoted the expression of downstream immune related genes of interleukin (IL)-6 and IL-8. These results unraveled the regulatory effect of pol-miR-155 in autophagy and in <i>E. tarda</i> infection.
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