Comparative analysis of RNA interference and pattern-triggered immunity induced by dsRNA reveals different efficiencies in the antiviral response to potato virus X.

Antiviral responses induced by double-stranded RNA (dsRNA) include RNA interference (RNAi) and pattern-triggered immunity (PTI), but their relative contributions to antiviral defence are not well understood. We aimed at testing the impact of exogenous applied dsRNA on both layers of defence against potato virus X expressing GFP (PVX-GFP) in Nicotiana benthamiana. Co-inoculation of PVX-GFP with either sequence-specific (RNAi) or nonspecific dsRNA (PTI) showed that nonspecific dsRNA reduced virus accumulation in both inoculated and systemic leaves.

Adaptive substitutions at two amino acids of HCPro modify its functional properties to separately increase the virulence of a potyviral chimera.

We had previously reported that a plum pox virus (PPV)-based chimera that had its P1-HCPro bi-cistron replaced by a modified one from potato virus Y (PVY) increased its virulence in some Nicotiana benthamiana plants, after mechanical passages. This correlated with the natural acquisition of amino acid substitutions in several proteins, including in HCPro at either position 352 (Ile→Thr) or 454 (Leu→Arg), or of mutations in non-coding regions. Thr in position 352 is not found among natural potyviruses, while Arg in 454 is a reversion to the native PVY HCPro amino acid.

Transgenerational Tolerance to Salt and Osmotic Stresses Induced by Plant Virus Infection.

Following pathogen infection, plants have developed diverse mechanisms that direct their immune systems towards more robust induction of defense responses against recurrent environmental stresses. The induced resistances could be inherited by the progenies, rendering them more tolerant to stressful events. Although within-generational induction of tolerance to abiotic stress is a well-documented phenomenon in virus-infected plants, the transgenerational inheritance of tolerance to abiotic stresses in their progenies has not been explored.

Adaptation of a Potyvirus Chimera Increases Its Virulence in a Compatible Host through Changes in HCPro.

A viral chimera in which the bi-cistron of a plum pox virus construct (PPV-GFP) was replaced by that of potato virus Y (PVY) spread slowly systemically in plants and accumulated to levels that were 5-10% those of parental PPV-GFP. We tested whether consecutive mechanical passages could increase its virulence, and found that after several passages, chimera titers rose and symptoms increased. We sequenced over half the genome of passaged chimera lineages infecting two plants.

Water Deficit Improves Reproductive Fitness in Plants Infected by .

Plants are concurrently exposed to biotic and abiotic stresses, including infection by viruses and drought. Combined stresses result in plant responses that are different from those observed for each individual stress. We investigated compensatory effects induced by virus infection on the fitness of hosts grown under water deficit, and the hypothesis that water deficit improves tolerance, estimated as reproductive fitness, to virus infection.

In planta vs viral expression of HCPro affects its binding of nonplant 21-22 nucleotide small RNAs, but not its preference for 5'-terminal adenines, or its effects on small RNA methylation.

Previous studies have found a correlation between the abilities of PVX vector-expressed HCPro variants to bind small RNAs (sRNAs), and to suppress silencing. Moreover, HCPro preferred to bind viral sRNAs of 21-22 nucleotides (nt) containing 5'-terminal adenines. This would require such viral sRNAs to have either different access to the suppressor than those of plant sequences, or different molecular properties.

Transcriptional responses of Hypericum perforatum cells to Agrobacterium tumefaciens and differential gene expression in dark glands.

Hypericum perforatum L. (St. John's wort) is a well-known medicinal plant that possesses secondary metabolites with beneficial pharmacological properties.

Molecular insights on potato yellow vein crinivirus infections in the highlands of Colombia.

(PYVV) was detected in potatoes grown in the Central highlands, north of Bogotá (~3000 m altitude), Colombia. At this altitude viral whitefly vectors are largely absent, but infection persists because of the use of uncertified tubers. Plants with typical PYVV-induced yellowing symptoms, as well as with atypical yellowing or non-symptomatic symptoms were sampled at three separate geographical locations.

Differences in Virulence among PVY Isolates of Different Geographical Origins When Infecting an Experimental Host under Two Growing Environments Are Not Determined by HCPro.

The contribution of the HCPro factors expressed by several PVY isolates of different geographical origins (one from Scotland, one from Spain, and several from Tunisia) to differences in their virulence in plants was investigated under two growing conditions: standard (st; 26 °C and current ambient levels of CO), and climate change-associated (cc; 31 °C and elevated levels of CO). In all cases, relative infection symptoms and viral titers were determined. The viral cistrons were also sequenced and amino-acid features of the encoded proteins were established, as well as phylogenetic distances.

Topical Application of -Encapsulated dsRNA Induces Resistance in to Potato Viruses and Involves RDR6 and Combined Activities of DCL2 and DCL4.

Exogenous application of double-stranded RNAs (dsRNAs) for inducing virus resistance in plants represents an attractive alternative to transgene-based silencing approaches. However, improvement of dsRNA stability in natural conditions is required in order to provide long-term protection against the targeted virus. Here, we tested the protective effect of topical application of -encapsulated dsRNA compared to naked dsRNA against single and dual infection by expressing the green fluorescent protein (PVX-GFP) and Potato virus Y (PVY) in .

Overexpression of polygalacturonase-inhibiting protein (PGIP) gene from Hypericum perforatum alters expression of multiple defense-related genes and modulates recalcitrance to Agrobacterium tumefaciens in tobacco.

Hypericum perforatum L is a remarkable source of high-value secondary metabolites with increasing applications in pharmaceutical industry. However, improvement in the production of secondary metabolites through genetic engineering is a demanding task, as H. perforatum is not amenable to Agrobacterium tumefaciens-mediated transformation.

Effects of a changing environment on the defenses of plants to viruses.

Since their appearance, plants have lived and evolved within changing environments that were determined by a host of abiotic and biotic factors. It is in this evolutionary context that both, the mechanisms of defense by plants against viruses and the viral reprogramming of plant routes were established, which combined define the outcomes of compatible infections. Current alterations in the chemistry of the atmosphere are causing changes in the global context in which plants and viruses interact that are unprecedented not in their nature but in their pace.

Transgenic expression of Hyp-1 gene from Hypericum perforatum L. alters expression of defense-related genes and modulates recalcitrance to Agrobacterium tumefaciens.

Phenolic oxidative coupling protein (Hyp-1) isolated from Hypericum perforatum L. was characterized as a defense gene involved in H. perforatum recalcitrance to Agrobacterium tumefaciens-mediated transformation Hypericum perforatum L.

Virus infection induces resistance to and to drought in both compatible and incompatible bacteria-host interactions, which are compromised under conditions of elevated temperature and CO levels.

Plants are simultaneously exposed to a variety of biotic and abiotic stresses, such as infections by viruses and bacteria, or drought. This study aimed to improve our understanding of interactions between viral and bacterial pathogens and the environment in the incompatible host and the susceptible host , and the contribution of viral virulence proteins to these responses. Infection by the (PVX)/ (PPV) pathosystem induced resistance to (Pst) and to drought in both compatible and incompatible bacteria-host interactions, once a threshold level of defence responses was triggered by the virulence proteins P25 of PVX and the helper component proteinase of PPV.

HCPro-mediated transmission by aphids of purified virions does not require its silencing suppression function and correlates with its ability to coat cell microtubules in loss-of-function mutant studies.

Native and amino acid (aa) substitution mutants of HCPro from potato virus Y (PVY) were transiently expressed in Nicotiana benthamiana leaves. Properties of those HCPro variants with regard to silencing suppression activities, mediation of viral transmission by aphids, and subcellular localization dynamics, were determined. One mutant failed to suppress silencing in agropatch assays, but could efficiently mediate the transmission by aphids of purified virions.

Cell death triggered by the P25 protein in Potato virus X-associated synergisms results from endoplasmic reticulum stress in Nicotiana benthamiana.

The synergistic interaction of Potato virus X (PVX) with a number of potyviruses results in systemic necrosis in Nicotiana spp. Previous investigations have indicated that the viral suppressor of RNA silencing (VSR) protein P25 of PVX triggers systemic necrosis in PVX-associated synergisms in a threshold-dependent manner. However, little is still known about the cellular processes that lead to this necrosis, and whether the VSR activity of P25 is involved in its elicitation.

Effects of simultaneously elevated temperature and CO levels on Nicotiana benthamiana and its infection by different positive-sense RNA viruses are cumulative and virus type-specific.

We have studied how simultaneously elevated temperature and CO levels [climate change-related conditions (CCC) of 30°C, 970 parts-per-million (ppm) of CO vs. standard conditions (SC) of 25°C, ~ 405ppm CO] affect physiochemical properties of Nicotiana benthamiana leaves, and also its infection by several positive-sense RNA viruses. In previous works we had studied effects of elevated temperature, CO levels separately.

Virulence determines beneficial trade-offs in the response of virus-infected plants to drought via induction of salicylic acid.

It has been hypothesized that plants can get beneficial trade-offs from viral infections when grown under drought conditions. However, experimental support for a positive correlation between virus-induced drought tolerance and increased host fitness is scarce. We investigated whether increased virulence exhibited by the synergistic interaction involving Potato virus X (PVX) and Plum pox virus (PPV) improves tolerance to drought and host fitness in Nicotiana benthamiana and Arabidopsis thaliana.

Identification of MAPKs as signal transduction components required for the cell death response during compatible infection by the synergistic pair Potato virus X-Potato virus Y.

Systemic necrosis is one of the most severe symptoms caused in compatible plant-virus interactions and shares common features with the hypersensitive response (HR). Mitogen-activated protein kinase (MAPK) cascades are associated with responses to compatible and incompatible host-virus interactions. Here, we show that virus-induced gene silencing of the Nicotiana benthamiana MAPK genes salicylic acid-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK), and the MAPK kinase (MAPKK) genes MEK1 and MKK1, partially compromised the HR-like response induced by the synergistic interaction of Potato virus X with Potato virus Y (PVX-PVY).

A Model to Explain Temperature Dependent Systemic Infection of Potato Plants by .

The effect of temperature on the rate of systemic infection of potatoes ( L. cv. Chu-Baek) by (PVY) was studied in growth chambers.

Potato Virus Y HCPro Suppression of Antiviral Silencing in Nicotiana benthamiana Plants Correlates with Its Ability To Bind to 21- and 22-Nucleotide Small RNAs of Viral Sequence.

We have investigated short and small RNAs (sRNAs) that were bound to a biologically active hexahistidine-tagged (PVY) HCPro suppressor of silencing, expressed from a heterologous virus vector in plants, and purified under nondenaturing conditions. We found that RNAs in purified preparations were differentially enriched in 21-nucleotide (nt) and, to a much lesser extent, 22-nt sRNAs of viral sequences (viral sRNAs [vsRNAs]) compared to those found in a control plant protein background bound to nickel resin in the absence of HCPro or in a purified HCPro alanine substitution mutant (HCPro mutB) control that lacked suppressor-of-silencing activity. In both controls, sRNAs were composed almost entirely of molecules of plant sequence, indicating that the resin-bound protein background had no affinity for vsRNAs and also that HCPro mutB failed to bind to vsRNAs.

Erratum: The Effects of High Temperature on Infection by Y, A, and .

[This corrects the article on p. 321 in vol. 32, PMID: 27493607.

The Effects of High Temperature on Infection by Potato virus Y, Potato virus A, and Potato leafroll virus.

We examined the effects of temperature on acquisition of Potato virus Y-O (PVY-O), Potato virus A (PVA), and Potato leafroll virus (PLRV) by Myzus persicae by performing transmission tests with aphids that acquired each virus at different temperatures. Infection by PVY-O/PVA and PLRV increased with increasing plant temperature in Nicotiana benthamiana and Physalis floridana, respectively, after being transmitted by aphids that acquired them within a temperature range of 10-20°C. However, infection rates subsequently decreased.

Effects of Elevated CO₂and Temperature on Pathogenicity Determinants and Virulence of Potato virus X/Potyvirus-Associated Synergism.

Infections of plants by multiple viruses are common in nature and may result in synergisms in pathologies. Several environmental factors influence plant-virus interactions and act on virulence and host defense responses. Mixed viral infections may be more frequent under environmental conditions associated with global warming.