Molecular characterization of two MAPK genes and their thermotolerant functions in a high temperature acclimated strain of Neoseiulus barkeri

Phytoseiid mites frequently experience stress under changing or fluctuating environments especially in hot and dry agroecosystems. The mitogen-activated protein kinase (MAPK) signaling pathway is known to mediate environmental stress response involved in different signaling transduction pathways. In this study, a high temperature acclimated strain (HTAS) of Neoseiulus barkeri Hughes was developed from a conventional strain (CS) based on our previous study, and the functional differences of two MAPK genes, NbJNK and Nbp38, involved in defense responses were determined between the two strains. At 42 degrees C, the relative gene expression levels of the two MAPK genes increased rapidly in both N. barkeri strains. The expressions, however, decreased with an increase in duration of thermal treatment in the CS, while they remained elevated after 4 h of heat treatment in the HTAS. Silencing of two NbHSP70 genes by RNA interference (RNAi) significantly suppressed the expression levels of NbJNK and Nbp38, indicating a positive correlation between the protective response of HSP70 proteins and activation of the MAPK pathway. Heterologous overexpression of exogenous proteins encoded by NbJNK and Nbp38 significantly enhanced the viability of Escherichia coli Escherich BL21 under lethal temperature conditions. These results suggested that the thermotolerance of HTAS may be related to the sustained accumulation of MAPK genes. Elucidation of the functions of the MAPK signaling pathway in phytoseiids provides a novel perspective to the development of sustainable control strategies for small sap-feeding pests under thermal stress environments.