Abstract
Tobacco Virgin A Mutant (VAM) exhibits apparent immunity to several potyviruses in a strain-specific manner. Its resistance was generated by UV irradiation, and is partially conditioned by the recessive gene va. This allele has been introgressed into several breeding fines such as NC745. Previously, it was observed that the inoculation of an avirulent strain of potato Y potyvirus (PVY(NN)) in both resistant genotypes, caused systemic infection in some NC745 plants only, and the virus recovered from these plants acquired an ability to easily infect both NC745 and VAM. The current study was to identify the host factors that define each one of these resistant phenotypes, and to characterize the pathogenic properties of the evolving virus. VAM cells supported a reduced rate of PVY(NN)-accumulation compared with NC745 cells, which accumulated virus progeny at, he same level as the susceptible control Burley 21 (B21). However, in both resistant tobaccos the virus cell-to-cell movement was similarly impaired. Even so, PVY(NN) was recovered sooner from NC745- than from VAM-inoculated leaves. After PVY(NN)-detection, emerging resistance breaking (RB) variants were also recovered. Surprisingly, just in VAM, the RB variants never moved out of the inoculated leaves, until they were reinoculated in the same or another uninoculated VAM plant. The inability of the emerging RB variants to exit the PVY(NN)-inoculated VAM leaves was associated with their low accumulation rate and an obstruction imposed by coinfecting avirulent genotypes. The VAM factor restricting virus accumulation was inherited independently from va and operated in an allele doses manner. This gene, named rvam2, was easily overcome by the isolated RB variants, but the underlying virus modification(s) implied a loss of fitness in B21. Thus, the systemic emergence of RB variants, starting from a quasispecies, adapted to accumulate in Rvam2 genotypes (e.g., B21), seems to require a high rate of local virus accumulation linked to a selective constraint in the virus intercellular and/or intertissular traffic. This is the first report where the combined action of two vulnerable resistance mechanisms confers a stronger plant resistance to a viral systemic infection.
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Claims 12
Claim · model-written summary
VAM cells supported less PVY(NN) accumulation than NC745 cells.
- Taxon
- VAMe0
- Material
- VAMe0
- Interactor
- PVY(NN)
Potato virus Ye0pathogen - Outcome
- PVY(NN)-accumulatione0
- Direction
- reducede0
- Comparator
- NC745e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“VAM cells supported a reduced rate of PVY(NN)-accumulation compared with NC745 cells”
Claim · model-written summary
NC745 accumulated PVY progeny at the same level as susceptible Burley 21.
Verbatim
e0“NC745 cells, which accumulated virus progeny at, he same level as the susceptible control Burley 21 (B21)”
Claim · model-written summary
PVY(NN) cell-to-cell movement was similarly impaired in VAM and NC745 tobacco.
- Taxon
- tobaccos
Nicotiana tabacume0 - Interactor
- viruse0pathogen
- Outcome
- virus cell-to-cell movemente0
- Direction
- impairede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“in both resistant tobaccos the virus cell-to-cell movement was similarly impaired”
e1“VAM cells supported a reduced rate of PVY(NN)-accumulation compared with NC745 cells”
Claim · model-written summary
PVY(NN) was recovered earlier from NC745 than VAM inoculated leaves.
- Taxon
- VAMe0
- Material
- NC745e0
- Organ / stage
- leavese0
- Interactor
- PVY(NN)Potato virus Ye0pathogen
- Outcome
- PVY(NN) was recoverede0
- Direction
- soonere0
- Comparator
- VAMe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“PVY(NN) was recovered sooner from NC745- than from VAM-inoculated leaves”
Claim · model-written summary
Resistance-breaking PVY variants were recovered after PVY(NN) detection.
- Interactor
- PVY(NN)Potato virus Ye0pathogen
- Outcome
- resistance breaking (RB) variants were also recoverede0
Not reportedTaxon
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“After PVY(NN)-detection, emerging resistance breaking (RB) variants were also recovered.”
t0“potato Y potyvirus”
Claim · model-written summary
In VAM, emerging resistance-breaking variants remained in inoculated leaves until reinoculation.
Verbatim
e0“just in VAM, the RB variants never moved out of the inoculated leaves, until they were reinoculated in the same or another uninoculated VAM plant”
Claim · model-written summary
Failure of emerging variants to leave VAM leaves was associated with low accumulation and obstruction by avirulent coinfecting genotypes.
- Taxon
- VAMe0
- Interactor
- RB variantse0pathogen
- Outcome
- inability of the emerging RB variants to exite0
- Qualifier
- low accumulation rate and an obstruction imposed by coinfecting avirulent genotypese0
Not reportedDirection
Verbatim
e0“The inability of the emerging RB variants to exit the PVY(NN)-inoculated VAM leaves was associated with their low accumulation rate and an obstruction imposed by coinfecting avirulent genotypes.”
Claim · model-written summary
The VAM accumulation restriction factor was inherited independently of va and showed allele-dose action.
Verbatim
e0“The VAM factor restricting virus accumulation was inherited independently from va and operated in an allele doses manner.”
Claim · model-written summary
Isolated resistance-breaking variants readily overcame rvam2.
Not reportedTaxon
Verbatim
e0“This gene, named rvam2, was easily overcome by the isolated RB variants”
Claim · model-written summary
The viral modification linked to overcoming rvam2 caused a fitness loss in B21.
Verbatim
e0“the underlying virus modification(s) implied a loss of fitness in B21”
Claim · model-written summary
The authors infer that systemic emergence of resistance-breaking variants requires high local viral accumulation plus constrained traffic.
Verbatim
e0“the systemic emergence of RB variants, starting from a quasispecies, adapted to accumulate in Rvam2 genotypes (e.g., B21), seems to require a high rate of local virus accumulation linked to a selective constraint in the virus intercellular and/or intertissular traffic”
Claim · model-written summary
Combining the two vulnerable resistance mechanisms conferred stronger resistance to systemic viral infection.
Verbatim
e0“the combined action of two vulnerable resistance mechanisms confers a stronger plant resistance to a viral systemic infection”