Molecular characterization of a novel wheat-infecting virus of the family Betaflexiviridae.

Wheat plants showing yellowing and mosaic in leaves and stunting were collected from wheat fields in Henan Province, China. Analysis of these plants by transmission electron microscopy showed that they contained two types of filamentous virus-like particles with a length of 200-500 nm and 1000-1300 nm, respectively. RNA-seq revealed a coinfection with wheat yellow mosaic virus (WYMV) and an unknown wheat-infecting virus. The genome of the unknown virus is 8,410 nucleotides long, excluding its 3' poly(A) tail. It has six open reading frames (ORFs). ORF1 encodes a putative viral replication-associated protein (Rep), and ORFs 2, 3, and 4 encode the triple gene block (TGB) proteins. ORFs 5 and 6 encode the capsid protein (CP) and a protein with unknown function, respectively. Phylogenetic analysis showed that this novel virus is evolutionarily related to members of the subfamily Quinvirinae, family Betaflexiviridae. It is, however, distinct from the viruses in the currently established genera. Based on the species and genus demarcation criteria set by the International Committee on Taxonomy of Viruses (ICTV), we tentatively name this novel virus "wheat yellow stunt-associated betaflexivirus" (WYSaBV), and we propose it to be a member of a new genus in the family Betaflexiviridae.