A novel virus-induced cyclic dinucleotide, 2′3′-c-di-GMP, mediates STING-dependent antiviral immunity inDrosophila

In mammals, the enzyme cGAS senses the presence of cytosolic DNA and synthesizes the cyclic dinucleotide (CDN) 2′3′-cGAMP. This CDN binds to and activates the protein STING to trigger immunity. We recently discovered in the model organismDrosophila melanogastertwo cGAS-like receptors (cGLRs) that activate STING-dependent antiviral immunity and can produce 3′2′-cGAMP, in addition to 2′3′-cGAMP. Here we explore CDN-mediated immunity in 14 differentDrosophilaspecies covering 50 million years of evolution and report that 2′3′-cGAMP and 3′2′-cGAMP fail to control infection byDrosophilaC virus inD. serrata, D. sechelliaandD. mojavensis. Using an accurate and sensitive mass spectrometry method, we discover an unexpected diversity of CDNs produced in a cGLR-dependent manner in response to viral infection inD. melanogaster, including a novel CDN, 2′3′-c-di-GMP. We show that 2′3′-c-di-GMP is the most potent STING agonist identified so far inD. melanogasterand that this molecule also activates a strong antiviral transcriptional response inD. serrata. Our results shed light on the evolution of cGLRs in flies and provide a basis for the understanding of the function and regulation of this emerging family of PRRs in animal innate immunity.