Functional analysis of two mitogen-activated protein kinases involved in thermal resistance of the predatory mite Neoseiulus californicus (Acari: Phytoseiidae)

Predatory mites are important biological control agents used against phytophagous mites and small insects. They face various environmental pressures, especially fluctuating climate factors. Neoseiulus californicus, a commercially available phytoseiid mite, is adapted to a wide range of temperature conditions. We investigated the regulatory mechanisms governing the plastic response of N. californicus for coping with environmental temperature variations. The mitogen-activated protein kinase (MAPK) signaling pathway is a highly conserved pathway of cell signal transduction that responds to environmental stress. We isolated two MAPKK genes (NcMAPKK4 and NcMAPKK6) from N. californicus and studied their functions. Developmental stage-specific expression level analysis showed that in adults, particularly females, NcMAPKK4 and NcMAPKK6 levels were higher than in other developmental stages. The expression level analysis at extremely high and low temperature conditions demonstrated that NcMAPKK4 could be induced significantly by adverse thermal stresses, whereas NcMAPKK6 distinctly responded to heat shock, indicating their different roles in thermal stress responses. After silencing of NcMAPKK4, both heat and cold resistance decreased significantly, whereas NcMAPKK6 knockdown had a greater influence on heat resistance. Knockdown of NcMAPKKs also reduced the activities of antioxidant enzymes, suggesting the regulation of NcMAPKKs was closely related to the antioxidant process in oxidative stress caused by external stimuli. These results indicate an important role of NcMAPKKs in the response to thermal stress and provide insight into the MAPK cascade pathway in the environmental adaptation mechanisms of phytoseiid mites.