Potato Leafroll Virus Accumulation Research Articles

The Three Essential Motifs in P0 for Suppression of RNA Silencing Activity of Potato leafroll virus Are Required for Virus Systemic Infection.

Higher plants exploit posttranscriptional gene silencing as a defense mechanism against virus infection by the RNA degradation system. Plant RNA viruses suppress posttranscriptional gene silencing using their encoded proteins. Three important motifs (F-box-like motif, G139/W140/G141-like motif, and C-terminal conserved region) in P0 of Potato leafroll virus (PLRV) were reported to be essential for suppression of RNA silencing activity. In this study, Agrobacterium-mediated transient experiments were carried out to screen the available amino acid substitutions in the F-box-like motif and G139/W140/G141-like motif that abolished the RNA silencing suppression activity of P0, without disturbing the P1 amino acid sequence. Subsequently, four P0 defective mutants derived from a full-length cDNA clone of PLRV (L76F and W87R substitutions in the F-box-like motif, G139RRR substitution in the G139/W140/G141-like motif, and F220R substitution in the C-terminal conserved region) were successfully generated by reverse PCR and used to investigate the impact of these substitutions on PLRV infectivity. The RT-PCR and western blot analysis revealed that these defective mutants affected virus accumulation in inoculated leaves and systemic movement in Nicotiana benthamiana as well as in its natural hosts, potato and black nightshade. These results further demonstrate that the RNA silencing suppressor of PLRV is required for PLRV accumulation and systemic infection.

Disruption of Chloroplast Function Through Downregulation of Phytoene Desaturase Enhances the Systemic Accumulation of an Aphid-Borne, Phloem-Restricted Virus.

Chloroplasts play a central role in pathogen defense in plants. However, most studies explaining the relationship between pathogens and chloroplasts have focused on pathogens that infect mesophyll cells. In contrast, the family Luteoviridae includes RNA viruses that replicate and traffic exclusively in the phloem. Recently, our lab has shown that Potato leafroll virus (PLRV), the type species in the genus Polerovirus, forms an extensive interaction network with chloroplast-localized proteins that is partially dependent on the PLRV capsid readthrough domain (RTD). In this study, we used virus-induced gene silencing to disrupt chloroplast function and assess the effects on PLRV accumulation in two host species. Silencing of phytoene desaturase (PDS), a key enzyme in carotenoid, chlorophyll, and gibberellic acid (GA) biosynthesis, resulted in a substantial increase in the systemic accumulation of PLRV. This increased accumulation was attenuated when plants were infected with a viral mutant that does not express the RTD. Application of GA partially suppressed the increase in virus accumulation in PDS-silenced plants, suggesting that GA signaling also plays a role in limiting PLRV infection. In addition, the fecundity of the aphid vector of PLRV was increased when fed on PDS-silenced plants relative to PLRV-infected plants.

Introgression of the Rl adg allele of resistance to potato leafroll virus in Solanum tuberosum L.

Abstract Genetic resistance to Potato Leafroll Virus (PLRV) is polygenic, which hinders the obtainment of resistant cultivars. However, works carried out at the International Potato Center have identified an andigena accession, LOP-868, with high resistance level and low accumulation of PLRV due to the gene of major effect Rladg. We verify the transfer of the Rladg allele to clones of the cross between LOP-868 and UFLA clones, by using the SCAR RGASC850 molecular marker; to evaluate the reaction of these clones to PLRV by inoculating the virus using aphids; and to analyze their agronomic performance of clones. Among the clones inoculated with viruliferous aphids, 49.3% were negative to the serological test, indicating possible resistance. Clones containing the Rladg allele were identified by the RGASC850 molecular marker, which demonstrates the possibility of transferring the Rladg allele of resistance to PLRV from LOP-868 to Solanum tuberosum. Some clones that presented the Rladg allele are also promising for agronomic performance.

High Levels of Heritable Resistance to Potato Leafroll Virus (PLRV) in Solanum tuberosum subsp. andigena

Phenotypic characterization and genetic studies were performed to provide fundamental information for the exploitation of the native cultivated potato species Solanum tuberosum subsp. andigena (Juz. and Bukasov.) Hawkes (andigena) as a source of resistance to Potato leafroll virus (PLRV). Analysis of a diallel mating design among andigena cultivars revealed the importance of additive gene effects. Phenotypic assessment of components of PLRV resistance showed that andigena cultivars with high levels of resistance to infection were also resistant to the accumulation of PLRV and able to restrict translocation of the virus to their tubers. Three andigena cultivars (LOP-868, HUA-332, and OCH-7643) identifi ed with these features also showed high positive general combining ability (GCA) for PLRV resistance. High frequencies of individuals in progenies from crosses between these cultivars and both resistant and susceptible commercial varieties were also resistant. No interaction in the expression of resistance from andigena in tuberosum backgrounds was observed indicating that breeding advances for this trait should proceed well using this new resistance source. Our results support the previous hypothesis that multiple components of resistance in a single genotype could be the result of a common mechanism controlled by several genes. The remarkably high frequency (>70%) of uninfected individuals in all progenies derived from the highly resistant andigena cultivar LOP-868 and the occurrence of highly resistant clones selected from this parent suggest the presence of an allele with large effects.

Characterization of the expression and inheritance of potato leafroll virus (PLRV) and potato virus Y (PVY) resistance in three generations of germplasm derived from Solanum etuberosum

Potato virus Y (PVY) and potato leafroll virus (PLRV) are two of the most important viral pathogens of potato. Infection of potato by these viruses results in losses of yield and quality in commercial production and in the rejection of seed in certification programs. Host plant resistance to these two viruses was identified in the backcross progeny of a Solanum etuberosum Lindl. somatic hybrid. Multiple years of field evaluations with high-virus inoculum and aphid populations have shown the PVY and PLRV resistances of S. etuberosum to be stably expressed in two generations of progeny. However, while PLRV resistance was transmitted and expressed in the third generation of backcrossing to cultivated potato (Solanum tuberosum L. subsp. tuberosum), PVY resistance was lost. PLRV resistance appears to be monogenic based on the inheritance of resistance in a BC(3) population. Data from a previous evaluation of the BC(2 )progeny used in this study provides evidence that PLRV resistance was partly conferred by reduced PLRV accumulation in foliage. The field and grafting data presented in this study suggests that resistance to the systemic spread of PLRV from infected foliage to tubers also contributes to the observed resistance from S. etuberosum. The PLRV resistance contributed by S. etuberosum is stably transmitted and expressed through sexual generations and therefore would be useful to potato breeders for the development of PLRV resistant potato cultivars.

Evidence that resistance to potato leafroll virus accumulation in tetraploidsolarium tuberosum L. is controlled by one or few major genes that are not complementary

Previous investigations into the inheritance of resistance to accumulation of potato leafroll virus indicated a dominant major-gene effect, but the segregation ratios in progenies of crosses were a closer fit to a model involving two complementary genes (both required for resistance and one present in the susceptible parent cultivar, Maris Piper) than to a single gene model. In this study, we tested the complementary gene hypothesis by backcrossing susceptible segregants from one of these progenies to their susceptible parent, Maris Piper. No resistant segregants were found in the five backcross progenies examined, so the complementary gene hypothesis was not supported. There was significant variation between susceptible progeny-members in these backcrosses. The progeny of another, highly resistant parent clone, G. 8107(1), selfed, was also examined: all members were resistant. Whilst there is evidently a dominant major-gene effect involved, this is not the whole picture and there are other unidentified genetic effects.

Inhibited Long‐Distance Movement of Potato Leafroll Virus to Tubers in Potato Genotypes Expressing Combined Resistance to Infection, Virus Multiplication and Accumulation

AbstractPlants of two potato clones which, in preliminary greenhouse assessments, showed resistance to multiplication and accumulation of potato leafroll virus (PLRV) were graft or aphid inoculated with the virus and grown in the greenhouse; plants of a moderately susceptible cultivar were used for comparison in all experiments. A high concentration of aphid‐borne inoculum was used to ensure strong infection pressure. Clone M62759 appeared to be highly resistant to PLRV infection, whereas clone PS1706 was more susceptible. Both clones expressed a high level of resistance to virus multiplication, when primary or secondary infection was assayed by enzyme‐linked immunosorbent assay. Moreover, PLRV was detected in only few or none of the progeny plants of clone M62759, which thus strongly inhibited virus transport to tubers. The study on PLRV translocation from aphid‐inoculated shoots to uninoculated shoots sprouted from the same tubers showed that no specific mechanisms are likely to impair PLRV movement through the tubers of the resistant genotypes. These results indicate that three valuable components of the resistance to PLRV are probably closely linked in the genotype, a combination that seems to occur rather rarely in potato clones. Nevertheless, selecting potato genotypes for the complex resistance to PLRV may prove to be a worthwhile part of breeding programmes, provided that the genetic mechanisms governing particular types of resistance are better recognized.

Characterisation of resistance to potato leafroll virus accumulation in Solanum phureja.

Strong resistance to accumulation of potato leafroll virus (PLRV) was identified in a clone of the diploid potato species Solanum phureja (cv. ‘Egg Yolk’, clone 5010) using a quantitative enzyme-linked immunosorbent assay (ELISA). The resistance is expressed very strongly in leaf tissue (virus could not be detected in leaves of some plants although other tissues were infected) but less strongly in petiole and stem tissue of infected plants. The titre of PLRV in leaves of S. phureja (5010) is approximately 2%, or less, of the titre in S. tuberosum cv. Maris Piper. The pattern of virus accumulation in different tissues of S. phureja (5010) and the distribution of virus-infected cells in phloem bundles suggest that this resistance is different to a similar form of resistance to PLRV accumulation previously identified in clones of Solanum tuberosum. Plants of S. phureja (5010) were transformed with the coat protein gene of potato leafroll virus (PLRV). Transgenic lines of S. phureja (5010) expressing transgene RNA transcript were no more resistant to aphid-borne infection with PLRV or to virus accumulation than were non-transgenic lines.

Within-Plant Accumulation of Potato Leafroll Virus by Aggregated Green Peach Aphid Feeding

Aggregates of 20 green peach aphids placed on noninoculated leaves of plants previously inoculated with potato leafroll virus (PLRV) caused significantly more accumulation of PLRV at their feeding sites than in aphid-free leaves in both potato and Physalis floridana. Based on comparable periods of postinoculation, six times more viral antigen was detected by enzyme-linked immunosorbent assay in inoculated leaves of P floridana than of potato. The amount of PLRV detected in inoculated leaves was significantly correlated with the amount of PLRV that accumulated in aggregate feeding leaves, indicating that systemic spread of PLRV was titer-dependent. The movement of PLRV to aggregated aphid feeding sites probably followed the path of metabolites directed to the site of aphid damage and/or nutrient withdrawal. The accumulation of PLRV was not specific to the area of aggregated feeding but was evident throughout the leaf supporting the aphid colony. Aphids feeding in aggregates provided a mechanism that optimized virus acquisition from infected plants in which the pathogen was not uniformly distributed.

Resistance to potato leafroll virus infection and accumulation in potato cultivars, and the effects of previous infection with other viruses on expression of resistance

A selection of potato cultivars and breeding lines was evaluated for presence of resistance to infection with potato leafroll virus (PLRV) via viruliferous aphid vectors ( IR) and/or resistance to accumulation of PLRV antigen ( AR) in infected leaf tissue. Cultivars Aracy, Delcora, Omega and Spunta, and breeding lines BR63.15 and B71.240.2 carried both IR and AR , Bismark, Serrana INTA and L/T1 had alone and Delaware had AR alone. The other cultivars tested had neither. Within both the resistant and susceptible classes for AR, the level of PLRV antigen accumulation achieved varied with cultivar. Previous infection with potato virus X (PVX) or potato virus S (PVS) either alone or together did not diminish the expression of IR or AR. However, the presence of PVX sometimes significantly increased the accumulation of PLRV in susceptible cv. Desiree and this effect was most pronounced in mature leaves of older plants. In contrast, presence of PVX in susceptible cv. Desiree did not increase the numbers of plants becoming infected with PLRV. Identifying potato genotypes with and IR AR will help the Australian potato industry to select cultivars which become infected with PLRV more slowly under conditions of high infection pressure and/or are suitable for use as parental lines in breeding virus-resistant cultivars.

Accumulation of potato virus Y is enhanced in Solatium brevidens also infected with tobacco mosaic virus or potato spindle tuber viroid

SummaryThe accumulation of potato virus Y˚(PVY˚) and potato leaf roll virus (PLRV) was studied in plants of Solanum brevidens co‐infected with each of six viruses or a viroid. Virus could not be detected by ELISA in plants of S. brevidens infected solely with PVY. However, accumulation of PVY was increased c. 1000‐fold in plants doubly infected with tobacco mosaic virus or potato spindle tuber viroid (PSTVd). PVY titres in doubly infected plants of S. brevidens were between 1% and 0.1% of those found in the PVY‐susceptible interspecific Solanum hybrid DTO‐33. Double infections of 5. brevidens by PVY and alfalfa mosaic virus or potato viruses M, S, T or X did not significantly enhance PVY accumulation. Accumulation of PLRV was not enhanced in plants co‐infected with any of the six viruses or PSTVd.

The Effects of Temperature on the Susceptibility of Potato Plants to Infection and Accumulation of Potato Leafroll Virus

Temperature both before and after aphid inoculation with potato leafroll virus (PLRV) greatly influenced the susceptibility of potato plants to infection and virus accumulation, as evaluated with ELISA using cultivars with different ratings for the resistance to PLRV. Pre-incubation at 15 compared to 27 °C increased the susceptibility of plants to infection and a subsequent PLRV accumulation. The virus was detected by ELISA in a greater proportion of plants and reached a higher concentration, when the plants were kept at 27 than at 15 °C after inoculation. The mean ELISA values obtained with PLRV-infected plants in the 15/27 combination of the pre-/post-inoculation temperatures over the period 1—6 wks after inoculation were significantly higher than those in the 27/27, 15/15 and 27/15 treatments, and the values obtained in the 27/27 treatment were significantly higher than those in the 15/15 and 27/15 ones. A hypersensitive-like intolerance reaction to PLRV occurred in the resistant cv. Irga only in the plants kept at 27 °C after inoculation.