The Anti-interferon Activity of Conserved Viral dUTPase ORF54 is Essential for an Effective MHV-68 Infection

Gammaherpesviruses such as KSHV and EBV establish lifelong persistent infections through latency in lymphocytes. These viruses have evolved several strategies to counteract the various components of the innate and adaptive immune systems. We conducted an unbiased screen using the genetically and biologically related virus, MHV-68, to find viral ORFs involved in the inhibition of type I interferon signaling and identified a conserved viral dUTPase, ORF54. Here we define the contribution of ORF54 in type I interferon inhibition by ectopic expression and through the use of genetically modified MHV-68. ORF54 and an ORF54 lacking dUTPase enzymatic activity efficiently inhibit type I interferon signaling by inducing the degradation of the type I interferon receptor protein IFNAR1. Subsequently, we show in vitro that the lack of ORF54 causes a reduction in lytic replication in the presence of type I interferon signaling. Investigation of the physiological consequence of IFNAR1 degradation and importance of ORF54 during MHV-68 in vivo infection demonstrates that ORF54 has an even greater impact on persistent infection than on lytic replication. MHV-68 lacking ORF54 expression is unable to efficiently establish latent infection in lymphocytes, although it replicates relatively normally in lung tissues. However, infection of IFNAR−/− mice alleviates this phenotype, emphasizing the specific role of ORF54 in type I interferon inhibition. Infection of mice and cells by a recombinant MHV-68 virus harboring a site specific mutation in ORF54 rendering the dUTPase inactive demonstrates that dUTPase enzymatic activity is not required for anti-interferon function of ORF54. Moreover, we find that dUTPase activity is dispensable at all stages of MHV-68 infection analyzed. Overall, our data suggest that ORF54 has evolved anti-interferon activity in addition to its dUTPase enzymatic activity, and that it is actually the anti-interferon role that renders ORF54 critical for establishing an effective persistent infection of MHV-68

Seed-dispersal mode and habitat connectivity underpin variation in carbon stocking between Brazilian biomes

In tropical forests, about 60%–80% of woody plant species depend on animal–plant interactions for dispersal. The dependence on animal species for dispersal makes this interaction very fragile in the face of anthropogenic changes in land use. Disrupting seed-dispersal processes, principally zoochoric dispersal, could significantly alter the long-term carbon storage potential of tropical forests. An important question is how landscape structure changes tree carbon stocks in different types of tropical vegetation and how variation is mediated by the dispersal mode of animal (zoochoric) or abiotic (non-zoochoric) seeds. We focused on tree plots at 126 sites in Brazil spanning four types of forest and savanna vegetation, and calculated carbon stored in zoochoric, non-zoochoric, and large frugivore-dispersed species. Our results showed that carbon stocks in zoochoric species and non-zoochoric species differ significantly among vegetation types, with rainforests having higher stocks in zoochoric species and deciduous seasonally dry tropical forests having higher values in non-zoochoric species. A greater area of native vegetation promotes higher proportions of carbon stocks dispersed by large frugivore species, whereas a higher mean shape index reduces this proportion. Synthesis. This study highlights that seed-dispersal type underpins the variation in carbon stocks between vegetation types and that the maintenance of habitat of large dispersers and connectivity are key for retaining carbon stocks in zoochoric species, particularly in rainforest and cerrado sensu stricto