Structure and its transformation of elliptical nege-like virus Tanay virus

Negeviruses that infect insects are recently identified virus species that are phylogenetically related to several plant viruses. They exhibit a unique virion structure, an elliptical core with a short projection. Negeviruses encode two structural proteins, a glycoprotein that forms a short projection, and an envelope protein that forms an elliptical core. The glycoprotein has been reported only in the negeviruses’ genes, and not in phylogenetically related plant viruses’ genes. In this report, we first describe the three-dimensional electron cryo-microscopy (cryo-EM) structure of Tanay virus (TANAV), one of the nege-like viruses. TANAV particle demonstrates a periodical envelope structure consisting of three layers surrounding the centered viral RNA. The elliptical core dynamically changes its shape under acidic and even low detergent conditions to form bullet-like or tubular shapes. The further cryo-EM studies on these transformed TANAV particles reveal their overall structural rearrangement. These findings suggest putative geometries of TANAV and its transformation in the life cycle, and the potential importance of the short projection for enabling cell entry to the insect hosts. Impact statement Negeviridae has recently been declared as a virus family that includes virus species exhibiting a unique particle structure that differs from other known viruses. They are known to be common mosquito viruses isolated around the world, but also phylogenetically related to several plant viruses that impair crop production. Therefore, the negeviruses may also play a role in plant ecosystems that threaten agriculture. However, the mechanism of infection and assembly of the negeviruses as well as their structure were unknown. In this study, intact and dissociated structures of the TANAV were first examined using cryo-EM single particle analysis (SPA) and electron cryo-tomography (cryo-ET). These results reveal new structural geometries of the TANAV particle and its dynamic transformation under acidic and even low-detergent conditions, providing new insights into the infection and assembly mechanism in negeviruses.