A c-Jun N-terminal kinase (JNK) homolog from Macrobrachium rosenbergii participates in immune defense against Aeromonas hydrophila.

c-Jun N-terminal kinase (JNK) is a key member of the mitogen-activated protein kinase (MAPK) family, playing a vital role in the innate immune response of crustaceans by regulating the expression of antimicrobial peptide (AMP) genes. This research aimed to isolate and characterize a JNK gene from Macrobrachium rosenbergii designated as MrJNK. The full-length cDNA of MrJNK consisted of 1455 bp with an open reading frame (ORF) of 1266 bp encoding 421 amino acids containing a conserved serine/threonine protein kinase catalytic (S_TKc) domain. The phylogenetic tree of JNK proteins indicated that MrJNK and JNK from M. nipponense (MnJNK) were closely related, and were classified within the same clade as other JNK proteins from various crustacean species. The expression analysis by real-time RT-PCR showed that MrJNK was expressed in all examined tissues demonstrating the highest expression in the hemocyte. Following an immune challenge with Aeromonas hydrophila, the transcriptional levels of MrJNK were significantly upregulated in gill, hepatopancreas, hemocyte, muscle, and intestine. The functional role of MrJNK was investigated using RNA interference (RNAi) assay. Knockdown of MrJNK by dsRNA resulted to significant downregulation of anti-lipopolysaccharide factor 5 (ALF5), crustin (Crs), mannose-binding lectin (MBL), lysozyme (Lyz), and prophenoloxidase (proPO) transcripts. In addition, the cumulative mortality rate in MrJNK-silenced M. rosenbergii was significantly increased after A. hydrophila injection. Moreover, the expression levels of two antimicrobial peptides (AMPs) and three immune-related genes were significantly inhibited after silencing MrJNK by dsRNA and A. hydrophila injection in prawns. These results indicate that MrJNK is required for normal transcription of these immune-related genes and is involved in the innate immune response of M. rosenbergii at the transcriptional level.