Movement Functions of Umbraviruses

Dissecting dynamic plant virus synergism in mixed infections of poleroviruses, umbraviruses, and tombusvirus-like associated RNAs

“…Genome maps of each of these viruses and the proteins they encode are depicted in Figure 1. It has also been found that some poleroviruses can, presumably, utilize the cell-to-cell movement proteins (MPs) of a co-infecting umbravirus, allowing the polerovirus to presumably escape phloem limitation and become mechanically transmissible (Hoffman et al, 2001;Ryabov et al, 2001a;Zhou et al, 2017). While there are a good number of studies on polerovirus-tlaRNA and polerovirus-umbravirus interactions, there currently exist few studies on umbravirus-tlaRNA interactions.…”

“…One is that co-infection functions to increase the replication of one or more co-infecting viruses, resulting in more viral copies per cell, as has been found in co-infections of the plant infecting reoviruses southern rice-black streaked dwarf virus (SRBSDV) and rice ragged stunt virus (RRSV), and for TuYV and ST9 in C. b-p. plants (Passmore et al, 1993;Li et al, 2017). Another possibility is that umbravirus encoded movement proteins interact with co-infecting heterologous viral RNAs to impart them with cell-to-cell and systemic movement within the plant thereby resulting in more cells being infected with the dependent virus, as has been observed in co-infections of the polerovirus potato leafroll virus (PLRV) with the umbravirus pea enation mosaic virus 2 (PEMV2; Ryabov et al, 2001a). This could explain the increase of TuYV accumulation in the presence of CMoV, since on its own TuYV is phloem limited and co-infection may help it break this phloem limitation.…”

“…TlaRNA ST9 was found to have a structural feature in the 3′ untranslated region (UTR) of its genomic RNA that functions to stall host XRN1 degradation (Campbell et al, 2022), which may explain the dramatic effect ST9 appeared to have on TuYV and CMoV accumulation in co-infected plants. The long distance movement protein (encoded by ORF3) of umbraviruses has been shown to form protective ribonucleoprotein complexes with both umbravirus and heterologous virus RNAs (Ryabov et al, 2001b;, and has also been shown in PEMV2 to protect (1979) showed that TuYV [formerly referred to as beet western yellows virus (BWYV)] was occasionally mechanically transmitted from plants co-infected with the umbravirus, lettuce speckles mottle virus (LSMV), and PLRV has been observed to gain mechanical transmissibility as a result of co-infection with PEMV2 (Falk et al, 1979;Ryabov et al, 2001a). In the latter study, it was also found that PLRV became mechanically transmissible when co-infected with a cucumber mosaic virus (CMV) vector engineered to express the GRV ORF4 protein, suggesting that this protein likely plays an important mechanistic role in mechanical transmission.…”