Family: Potyviridae

Genus: Poacevirus

Distinguishing features

Triticum mosaic virus (TriMV) is transmitted by the wheat curl mite (Aceria tosichella) and has an unusually long 5´-untranslated region. Vectors are unknown for the other members of the genus.

Virion

Morphology

Virions of sugarcane streak mosaic virus (SCSMV) are flexuous filaments 890 nm×15 nm in size.

Nucleic acid

Virions contain a positive-sense ssRNA of 9.7–10.2 kb with a 3′-poly(A) terminus.

Proteins

The TriMV CP is a single peptide of 293 aa with a MW of about 32 kDa. For SCSMV the viral CP is 281 aa in size with the MW estimated to be 36 kDa. Caladenia virus A (CalVA) has a CP of 285 aa and MW of 31 kDa.

Genome organization and replication

The TriMV genome consists of 10,266 nt (Figure 1.Poacevirus). The genome encodes a polyprotein of 3,122 aa. TriMV has an unusually long 5´-untranslated region, but this is not shared by members of the other two species. The order of coding regions is typical of that of the potyviruses (Figure 2.Potyviridae). Most known potyvirus motifs are present in the polyprotein of poaceviruses. The aphid transmission amino acid sequence motifs present in the HC-Pros (KITC, PTK) and CPs (DAG) of potyviruses are absent in poaceviruses. The zinc-finger-like motif H-(X₂)-C-(X₂₉)-C-(X₂)-C in the tritimovirus wheat streak mosaic virus (WSMV) HC-Pro is essential for its transmission by mites. A similar motif in the poacevirus CalVA (unknown vector) is present as H-(X₂)-H-(X₂₉)-C-(X₂)-C (Wylie et al., 2012). In TriMV (mite transmitted) and SCSMV (unknown vector), the C-(X₂)-C motif exists, but the remainder of the motif is incomplete. P1 rather than the HC-Pro suppresses the host RNA-suppression response in TriMV (Tatineni et al., 2012). Members of the genus Poacevirus are phylogenetically closer to those of another mite-transmitted genus, Tritimovirus.

Figure 1.Poacevirus Schematic diagram of Triticum mosaic virus (TriMV) genome. The polyprotein ORF is indicated by the large open box divided into putative mature proteins. The pretty interesting Potyviridae protein (PIPO) is represented by a small box. The untranslated regions (UTR) are represented by lines on each end of the large ORF. Activities of mature proteins are postulated by analogy with genus Potyvirus. Conventions are as for the potyvirus genome organization map (Figure 2.Potyviridae). Not to scale.

Biology

Host range

TriMV and SCSMV only infect hosts in the Poaceae, while CalVA infects orchids (Wylie et al., 2012).

Transmission

TriMV is transmitted by the wheat curl mite (Aceria tosichella).

Antigenicity

An antiserum raised against SCSMV weakly cross-reacts with WSMV capsid protein in Western blot analysis. SCSMV does not cross-react with other sugarcane-infecting members of the family Potyviridae.

Species demarcation criteria

See discussion under family description.