Rickettsial Pathogen Perturbs Tick Circadian Gene to Infect the Vertebrate Host.

is a medically important tick that transmits several microbes to humans, including rickettsial pathogen . In nature, these ticks encounter several abiotic factors including changes in temperature, humidity, and light. Many organisms use endogenously generated circadian pathways to encounter abiotic factors. In this study, we provide evidence for the first time to show that modulates the arthropod circadian gene for its transmission to the vertebrate host. We noted a circadian oscillation in the expression of arthropod , , and genes when ticks or tick cells were exposed to alternate 12 h light: 12 h dark conditions. Moreover, significantly modulates the oscillation pattern of expression of these genes. In addition, increased levels of and and decreased expression of Toll and JAK/STAT pathway immune genes such as and respectively, were noted during transmission from ticks to the vertebrate host. RNAi-mediated knockdown of gene expression in ticks resulted in the reduced expression of and that increased bacterial transmission from ticks to the murine host. Furthermore, -deficient ticks fed late and had less engorgement weights. These results indicate an important role for circadian modulation of tick gene expression that is critical for arthropod blood feeding and transmission of pathogens from vector to the vertebrate host.