Molecular Technology for Isolation and Characterization of Mitogen-Activated Protein Kinase Kinase 4 from Penaeus monodon, and the Response to Bacterial Infection and Low-Salinity Challenge

Mitogen-activated protein kinase kinase 4 (MKK4) is a component of the JNK signaling pathway and plays an important role in immunity and stress resistance. In this study, MKK4 cDNA was cloned, and its bacterial infection and low-salinity challenge responses were researched. The full-length PmMKK4 cDNA was 1582 bp long, with an 858-bp open reading frame (ORF) encoding a 285-amino acid (aa) protein. Results showed that PmMKK-4 was expressed in all examined tissues of P. monodon. The PmMKK4 expression level was found to be lowest in eyestalk ganglion and highest in muscle (approximately 41.25 times than in eyestalk ganglion). Following the infection of Staphylococcus aureus, PmMKK4 was up-regulated in both hepatopancreatic and gill tissues. However, after infection with Vibrio harveyi, PmMKK4 was down-regulated for a period of time in gill tissue, with fluctuating up- and down-regulation in hepatopancreas tissue. Furthermore, after infection with Vibrio anguillarum, gill tissue and hepatopancreas tissue showed a continuous downward trend. The PmMKK4 gene in the gill tissue and hepatopancreas tissue of P. monodon was activated after low-salinity stress. The expression change of PmMKK4 in gill tissue was more significant. The research showed that the PmMKK4 gene plays an important role in both innate immunities after pathogen infection and adaptation in a low-salt environment.