Genus: Poacevirus

Distinguishing features

Triticum mosaic virus is transmitted by the wheat curl mite and has an unusually long 5’ untranslated region. The vectors are currently unknown for the other members of the genus.

Virion

Morphology

Virions of SCSMV are flexuous filaments 890 nm×15 nm in size.

Nucleic acid

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

Proteins

The TriMV CP is a single peptide of 293 aa, and its MW is about 32 kDa. For SCSMV the viral CP is 281 aa with the MW estimated to be 36 kDa. CalVA has a CP of 285 aa and MW of 31.

Genome organization and replication

The TriMV genome consists of 10,266 nt. The genome encodes a polyprotein of 3122 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 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 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., 2012:22914963RJOHTXWylie et al., 2012, Caladenia virus A, an unusual new member of the family Potyviridae from terrestrial orchids in Western Australia, Arch Virol, 157, 12, 2447-52}]. In TriMV (mite transmitted) and SCSMV (unknown vector), the C-(X₂)-C motif exists, but the remainder of the motif is incomplete. The P1 rather than the HC-Pro suppresses the host RNA-suppression response in TriMV [{Tatineni et al., 2012:22877841RJOHTXTatineni et al., 2012, Triticum mosaic poacevirus enlists P1 rather than HC-Pro to suppress RNA silencing-mediated host defense, Virology, 433, 1, 104-15}]. Members of the genus Poacevirus are phylogenetically closest to those of another mite-transmitted genus, Tritimovirus.

Antigenicity

A Western blot revealed that antiserum raised to SCSMV weakly cross-reacts with wheat streak mosaic virus capsid protein. SCSMV did not cross react with other sugarcane-infecting members of the Potyviridae.

Biology

Host range

TriMV and SCSMV only infect hosts in the Gramineae, while CalMV infects orchids [{Wylie et al., 2012:22914963RJOHTXWylie et al., 2012, Caladenia virus A, an unusual new member of the family Potyviridae from terrestrial orchids in Western Australia, Arch Virol, 157, 12, 2447-52}].

Transmission

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

Derivation of names

Poace: from Poaceae, the family name of the hosts of two member species.

 Member Species