Dicer-2 mutations in Aedes aegypti cells lead to a diminished antiviral function against Rift Valley fever virus and Bunyamwera virus infection

Mosquitoes are known to transmit different arthropod-borne viruses belonging to various virus families. The exogenous small interfering RNA pathway plays an important role in the mosquito defence against such virus infections, with Dicer-2 (Dcr2) as one of the key proteins that initiates the cleavage of viral dsRNAs into 21 nt long virus-derived small interfering RNAs. Previous data identified the importance of various motifs in Dcr2 for its small interfering RNA (siRNA)-mediated antiviral activity. However, all these data focus on positive-strand RNA viruses, although negative-strand RNA viruses, like <i>Bunyaviricetes</i>, include several important mosquito-borne viruses. Here, we aim to investigate the importance of different domains of Dcr2 for antiviral activity against viruses of the <i>Bunyaviricetes</i>. For this, we used the <i>Aedes aegypti-</i>derived Dcr2 knock-out cell line Aag2-AF319 to study the importance of the helicase, RNase III and PIWI-Argonaute-Zwille domains of Dcr2 on the antiviral activity of two viruses belonging to different families of the <i>Bunyaviricetes</i>: the Rift Valley fever virus (RVFV) vaccine strain MP12 (<i>Phenuiviridae</i>, <i>Phlebovirus</i>) and the Bunyamwera orthobunyavirus (BUNV; <i>Peribunyaviridae</i>, <i>Orthobunyavirus</i>). All three domains were determined to be critical for the antiviral activity against both RVFV and BUNV. Interestingly, one specific mutation in the helicase domain (KN) did not result in a loss of antiviral activity for RVFV, but for BUNV, despite losing the ability to produce 21 nt siRNAs.