Structural proteins of three viruses in the Potyviridae adhere only to their homologous cylindrical inclusions in mixed infections.

Immunoelectron microscopy of serial sections of leaf cells of wheat doubly infected by wheat streak mosaic virus and Agropyron mosaic virus or wheat spindle streak mosaic virus showed that structural proteins or virions associated only with homologous cylindrical inclusions (CI) or with self in aggregates. CI protein of WSMV was seen firmly attached to, and extended through, a plasmodesma. Based on CI protein similarities with transport protein families, membrane-associated secretion proteins, other transport proteins in the GTPase superfamily, and the here reported findings, it is suggested that CI proteins could serve as cell-to-cell movement proteins in the Potyviridae.