Recognition and function analysis of MKK6 in immune reaction against Vibrio Parahaemolyticus in Crassostrea hongkongensis

MKK6 is a key protein kinase that regulates inflammatory response under pathogen infection by activating MAPK signal pathway. However, the function of MKK6 remained unclear within oysters. Our research recognized a novel KK6 gene from C. hongkongensis, which is named ChMKK6. The cDNA of ChMKK6 gene was 2,760 bp in length, containing an ORF of 1,032 bp encoding 344 amino acids, with a conserved S-TKc region and a DVD region. As illustrated by amino acid alignment and phylogenetic tree, ChMKK6 shared the maximal (99.0%) identity showing MKK6 of Crassostrea gigas. As indicated by tissue expression analysis, ChMKK6 possessed the maximal expression within hepatopancreas, and was markedly increased in all tissues following Vibrio Parahaemolyticus (V. Parahaemolyticus) challenge. As stated by the qRT-PCR analysis, ChMKK6 silencing significantly suppressed IL17 transcription, suggesting its involvement in innate immunity by regulating IL17-mediated inflammatory response. Moreover, ChMKK6 silencing led to the suppression of key immune-related enzyme activities (ACP, AKP, CAT, LZM, and SOD), while raising the MDA content in gill. In addition, the antimicrobial viability of hemolymph supernatant was markedly reduced by ChMKK6 silencing. These results collectively demonstrate that ChMKK6 is a key player in immunity defense of C. hongkongensis from V. Parahaemolyticus.