Tritimoviruses are transmitted by mites (but different from those that transmit rymoviruses). They form a distinctive phylogenetic cluster.
Virions are flexuous filaments 690–700 nm long.
Physicochemical and physical properties
Virion S20,w is 166S for wheat streak mosaic virus (WSMV).
Virions contain a positive sense ssRNA, about 9.4–9.6 kb in size, with a 3′-poly(A) terminus.
The viral CP is a single peptide of about 349 aa for WSMV and 320 aa for brome streak mosaic virus (BrSMV). The Mr estimated by electrophoresis is about 42 kDa.
Genome organization and replication
The WSMV genome consists of 9384 nt excluding the 3′-terminal poly(A) tail. Sequence analysis reveals an ORF of 3035 aa. The structure and organization of the WSMV genome is similar to those of other members of the family Potyviridae except the bymoviruses (Figure 2.Potyviridae). Most known potyvirus motifs are present in the polyprotein of WSMV. However, motifs in the putative helper-component and CP of BrSMV are incomplete or missing, which may account for different vector relations of the tritimoviruses. The WSMV CP sequence shows limited (22-25%) identity with CP sequences of some aphid-transmitted potyviruses. WSMV shows significant aa sequence identity with aphid-transmitted potyviruses in the cylindrical inclusion protein and portions of the nuclear inclusion proteins. WSMV RNA has been translated in vitro into several large proteins immunoprecipitable with WSMV CP antiserum, suggesting that WSMV uses a proteolytic processing strategy to express functional proteins such as the CP. Antiserum to TEV 58 kDa nuclear inclusion protein also reacts with in vitro translation products of WSMV. An in vitro translation product is precipitated with antiserum to HC-Pro helper component of an isolate of the species Tobacco vein mottling virus. Comparative sequence analyses show similarities with other members of the family Potyviridae, but these are limited to the nine mature proteins. WSMV is especially susceptible to proteinases in planta and has CP molecules of 42, 36 and 32 kDa; the two smaller proteins are parts of the 42 kDa protein.
Moderately immunogenic. WSMV and oat necrotic mottle virus (ONMV) are serologically related to each other, but not to the other members of the family Potyviridae.
The viruses only affect hosts in the Gramineae but while WSMV has a wide host range BrSMV and ONMV have narrow ones.
WSMV and BrSMV are transmitted by eriophyid mites in a semi-persistent manner. The HC-Pro of WSMV is required for mite transmission. All definitive tritimoviruses are transmissible experimentally by mechanical inoculation.
Derivation of names
Tritimo: Triti*** and mosaic. From the symptoms induced on its host by isolates of the type species Wheat streak mosaic virus
Species Virus name Isolate Accession number RefSeq number Available sequence Virus Abbrev. Brome streak mosaic virus brome streak mosaic virus FR Z48506 NC_003501 Complete coding genome BrSMV Oat necrotic mottle virus oat necrotic mottle virus Type-NE AY377938 NC_005136 Complete genome ONMV Tall oatgrass mosaic virus tall oatgrass mosaic virus Benesov KF260962 NC_022745 Complete genome TOgMV Wheat eqlid mosaic virus wheat Eqlid mosaic virus IR EF608612 NC_009805 Complete genome WEqMV Wheat streak mosaic virus wheat streak mosaic virus Sidney 81 AF057533 NC_001886 Complete genome WSMV Yellow oat grass mosaic virus yellow oat-grass mosaic virus Sb KF984546 NC_024471 Complete genome YOgMV