ABSTRACT
Bats (order Chiroptera) are a major reservoir for emerging and re-emerging zoonotic viruses. Their tolerance towards highly pathogenic human viruses led to the hypothesis that bats may possess an especially active antiviral interferon (IFN) system. Here, we cloned and functionally characterized the virus RNA sensor, Retinoic Acid-Inducible Gene-I (RIG-I), from the "microbat" Myotis daubentonii (suborder Yangochiroptera) and the "megabat" Rousettus aegyptiacus (suborder Yinpterochiroptera), and compared them to the human ortholog. Our data show that the overall sequence and domain organization is highly conserved and that all three RIG-I orthologs can mediate a similar IFN induction in response to viral RNA at 37{degrees} and 39{degrees}C, but not at 30{degrees}C. Like human RIG-I, bat RIG-Is were optimally activated by double stranded RNA containing a 5'-triphosphate end and required Mitochondrial Antiviral-Signalling Protein (MAVS) for antiviral signalling. Moreover, the RIG-I orthologs of humans and of R. aegyptiacus, but not of M. daubentonii, enable innate immune sensing of SARS-CoV-2 infection. Our results thus show that microbats and megabats express a RIG-I that is not substantially different from the human counterpart with respect to function, temperature dependency, antiviral signaling, and RNA ligand properties, and that human and megabat RIG-I are able to sense SARS-CoV-2 infection.