Viruses pose a great threat to animal and plant health worldwide, with many being dependent on insect vectors for transmission between hosts. While the virus-host arms race has been well established, how viruses and insect vectors adapt to each other remains poorly understood. Begomoviruses comprise the largest genus of plant-infecting DNA viruses and are exclusively transmitted by the whitefly Bemisia tabaci. Here, we show that the vector Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway plays an important role in mediating the adaptation between the begomovirus tomato yellow leaf curl virus (TYLCV) and whiteflies. We found that the JAK/STAT pathway in B. tabaci functions as an antiviral mechanism against TYLCV infection in whiteflies as evidenced by the increase in viral DNA and coat protein (CP) levels after inhibiting JAK/STAT signaling. Two STAT-activated effector genes, BtCD109-2 and BtCD109-3, mediate this anti-TYLCV activity. To counteract this vector immunity, TYLCV has evolved strategies that impair the whitefly JAK/STAT pathway. Infection of TYLCV is associated with a reduction of JAK/STAT pathway activity in whiteflies. Moreover, TYLCV CP binds to STAT and blocks its nuclear translocation, thus, abrogating the STAT-dependent transactivation of target genes. We further show that inhibition of the whitefly JAK/STAT pathway facilitates TYLCV transmission but reduces whitefly survival and fecundity, indicating that this JAK/STAT-dependent TYLCV-whitefly interaction plays an important role in keeping a balance between whitefly fitness and TYLCV transmission. This study reveals a mechanism of plant virus-insect vector coadaptation in relation to vector survival and virus transmission.
Keywords: JAK/STAT; begomovirus; insect vector; virus transmission; whitefly.