Abstract
The signature feature of all plant viruses is the encoding of movement proteins (MPs) that supports the movement of the viral genome into adjacent cells and through the vascular system. The recent discovery of umbravirus-like viruses (ULVs), some of which only encode replication-associated proteins, suggested that they, as with umbraviruses that lack encoded capsid proteins (CPs) and silencing suppressors, would require association with a helper virus to complete an infection cycle. We examined the infection properties of 2 ULVs: citrus yellow vein associated virus 1 (CY1), which only encodes replication proteins, and closely related CY2 from hemp, which encodes an additional protein (ORF5CY2) that was assumed to be an MP. We report that both CY1 and CY2 can independently infect the model plant Nicotiana benthamiana in a phloem-limited fashion when delivered by agroinfiltration. Unlike encoded MPs, ORF5CY2 was dispensable for infection of CY2, but was associated with faster symptom development. Examination of ORF5CY2 revealed features more similar to luteoviruses/poleroviruses/sobemovirus CPs than to 30K class MPs, which all share a similar single jelly-roll domain. In addition, only CY2-infected plants contained virus-like particles (VLPs) associated with CY2 RNA and ORF5CY2. CY1 RNA and a defective (D)-RNA that arises during infection interacted with host protein phloem protein 2 (PP2) in vitro and in vivo, and formed a high molecular weight complex with sap proteins in vitro that was partially resistant to RNase treatment. When CY1 was used as a virus-induced gene silencing (VIGS) vector to target PP2 transcripts, CY1 accumulation was reduced in systemic leaves, supporting the usage of PP2 for systemic movement. ULVs are therefore the first plant viruses encoding replication and CPs but no MPs, and whose systemic movement relies on a host MP. This explains the lack of discernable helper viruses in many ULV-infected plants and evokes comparisons with the initial viruses transferred into plants that must have similarly required host proteins for movement.
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Claims 11
Claim · model-written summary
CY1 independently infected Nicotiana benthamiana and remained phloem limited after agroinfiltration.
- Taxon
- Nicotiana benthamiana
Nicotiana benthamianae0 - Treatment
- agroinfiltratione0
- Interactor
- CY1e0pathogen
- Outcome
- independently infecte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“both CY1 and CY2 can independently infect the model plant Nicotiana benthamiana in a phloem-limited fashion when delivered by agroinfiltration”
Claim · model-written summary
CY2 independently infected Nicotiana benthamiana and remained phloem limited after agroinfiltration.
- Taxon
- Nicotiana benthamianaNicotiana benthamianae0
- Treatment
- agroinfiltratione0
- Interactor
- CY2e0pathogen
- Outcome
- independently infecte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“both CY1 and CY2 can independently infect the model plant Nicotiana benthamiana in a phloem-limited fashion when delivered by agroinfiltration”
Claim · model-written summary
ORF5CY2 was dispensable for CY2 infection.
Verbatim
e0“ORF5CY2 was dispensable for infection of CY2”
t0“plant infection”
Claim · model-written summary
ORF5CY2 was associated with faster symptom development.
Verbatim
e0“ORF5CY2 was dispensable for infection of CY2, but was associated with faster symptom development”
t0“plant infection”
Claim · model-written summary
ORF5CY2 features resembled viral capsid proteins more than 30K class movement proteins.
Verbatim
e0“ORF5CY2 revealed features more similar to luteoviruses/poleroviruses/sobemovirus CPs than to 30K class MPs”
t0“plant infection”
Claim · model-written summary
Virus-like particles associated with CY2 RNA and ORF5CY2 occurred only in CY2-infected plants.
- Taxon
- plantsViridiplantaee0
- Interactor
- CY2e0pathogen
- Gene
- ORF5CY2e0
- Outcome
- virus-like particles (VLPs) associated with CY2 RNA and ORF5CY2e0
Verbatim
e0“only CY2-infected plants contained virus-like particles (VLPs) associated with CY2 RNA and ORF5CY2”
Claim · model-written summary
CY1 RNA interacted with host PP2 in vitro and in vivo.
Verbatim
e0“CY1 RNA and a defective (D)-RNA that arises during infection interacted with host protein phloem protein 2 (PP2) in vitro and in vivo”
t0“plant infection”
Claim · model-written summary
A CY1-associated defective RNA interacted with host PP2 in vitro and in vivo.
Verbatim
e0“CY1 RNA and a defective (D)-RNA that arises during infection interacted with host protein phloem protein 2 (PP2) in vitro and in vivo”
t0“plant infection”
Claim · model-written summary
CY1 RNA and defective RNA formed an RNase-resistant high molecular weight complex with sap proteins in vitro.
Verbatim
e0“formed a high molecular weight complex with sap proteins in vitro that was partially resistant to RNase treatment”
e1“CY1 RNA and a defective (D)-RNA”
t0“plant infection”
Claim · model-written summary
Targeting PP2 transcripts with a CY1 VIGS vector reduced CY1 accumulation in systemic leaves.
- Taxon
- plantt0
- Organ / stage
- systemic leavese0
- Treatment
- virus-induced gene silencing (VIGS) vector to target PP2 transcriptse0
- Interactor
- CY1e0pathogen
- Gene
- PP2e0
- Outcome
- CY1 accumulatione0
- Direction
- reducede0
Not reportedComparator
Verbatim
e0“When CY1 was used as a virus-induced gene silencing (VIGS) vector to target PP2 transcripts, CY1 accumulation was reduced in systemic leaves”
t0“plant infection”
Claim · model-written summary
The authors infer that ULV systemic movement relies on a host movement protein.
Verbatim
e0“ULVs are therefore the first plant viruses encoding replication and CPs but no MPs, and whose systemic movement relies on a host MP”
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