Multiple Nucleocapsid Structural Forms of Shrimp White Spot Syndrome Virus Suggests a Novel Viral Morphogenetic Pathway

White spot syndrome virus (WSSV) is a very large dsDNA virus. The accepted shape of the WSSV virion has been as ellipsoidal, with a tail-like extension. However, due to the scarcity of reliable references, the pathogenesis and morphogenesis of WSSV are not well understood. Here, we used transmission electron microscopy (TEM) and cryogenic electron microscopy (Cryo-EM) to address some knowledge gaps. We concluded that mature WSSV virions with a stout oval-like shape do not have tail-like extensions. Furthermore, there were two distinct ends in WSSV nucleocapsids: a portal cap and a closed base. A C14 symmetric structure of the WSSV nucleocapsid was also proposed, according to our Cryo-EM map. Immunoelectron microscopy (IEM) revealed that VP664 proteins, the main components of the 14 assembly units, form a ring-like architecture. Moreover, WSSV nucleocapsids were also observed to undergo unique helical dissociation. Based on these new results, we propose a novel morphogenetic pathway of WSSV.

Automated summary

Transmission electron microscopy (TEM) and cryogenic electron microscopy (Cryo-EM) techniques were used to study the morphology and pathogenesis of White spot syndrome virus (WSSV). The mature WSSV virions were found to have an oval shape without tail-like extensions. Two distinct ends, a portal cap, and a closed base, were observed in WSSV nucleocapsids. A C14 symmetric structure of the WSSV nucleocapsid was proposed based on Cryo-EM map. Immunoelectron microscopy (IEM) revealed a ring-like architecture formed by VP664 proteins, the main components of the 14 assembly units, in WSSV. Furthermore, a unique helical dissociation process of WSSV nucleocapsids was observed. Based on these findings, a novel morphogenetic pathway of WSSV was proposed.