Potato virus Y infection hinders potato defence response and renders plants more vulnerable to Colorado potato beetle attack

Protein complexes from edible mushrooms as a sustainable potato protection against coleopteran pests

Protein complexes from edible oyster mushrooms (Pleurotus sp.) composed of pleurotolysin A2 (PlyA2) and pleurotolysin B (PlyB) exert toxicity in feeding tests against Colorado potato beetle (CPB) larvae, acting through the interaction with insect-specific membrane sphingolipid. Here we present a new strategy for crop protection, based on in planta production of PlyA2/PlyB protein complexes, and we exemplify this strategy in construction of transgenic potato plants of cv Désirée. The transgenics in which PlyA2 was directed to the vacuole and PlyB to the endoplasmic reticulum are effectively protected from infestation by CPB larvae without impacting plant performance. These transgenic plants showed a pronounced effect on larval feeding rate, the larvae feeding on transgenic plants being on average five to six folds lighter than larvae feeding on controls. Further, only a fraction (11%-37%) of the larvae that fed on transgenic potato plants completed their life cycle and developed into adult beetles. Moreover, gene expression analysis of CPB larvae exposed to PlyA2/PlyB complexes revealed the response indicative of a general stress status of larvae and no evidence of possibility of developing resistance due to the functional inactivation of PlyA2/PlyB sphingolipid receptors.

Cold plasma within a stable supercavitation bubble - A breakthrough technology for efficient inactivation of viruses in water

Water scarcity, one of the most pressing challenges we face today, has developed for many reasons, including the increasing number of waterborne pollutants that affect the safety of the water environment. Waterborne human, animal and plant viruses represent huge health, environmental, and financial burden and thus it is important to efficiently inactivate them. Therefore, the main objective of this study was to construct a unique device combining plasma with supercavitation and to evaluate its efficiency for water decontamination with the emphasis on inactivation of viruses. High inactivation (>5 log10 PFU/mL) of bacteriophage MS2, a human enteric virus surrogate, was achieved after treatment of 0.43 L of recirculating water for up to 4 min. The key factors in the inactivation were short-lived reactive plasma species that damaged viral RNA. Water treated with plasma for a short time required for successful virus inactivation did not cause cytotoxic effects in the in vitro HepG2 cell model system or adverse effects on potato plant physiology. Therefore, the combined plasma-supercavitation device represents an environmentally-friendly technology that could provide contamination-free and safe water.

Molecular and Functional Analyses of Characterized Sesquiterpene Synthases in Mushroom-Forming Fungi

Sesquiterpenes are a type of abundant natural product with widespread applications in several industries. They are biosynthesized by sesquiterpene synthases (STSs). As valuable and abundant biological resources, mushroom-forming fungi are rich in new sesquiterpenes and STSs, which remain largely unexploited. In the present study, we collected information on 172 STSs from mushroom-forming fungi with experimentally characterized products from the literature and sorted them to develop a dataset. Furthermore, we analyzed and discussed the phylogenetic tree, catalytic products, and conserved motifs of STSs. Phylogenetic analysis revealed that the STSs were clustered into four clades. Furthermore, their cyclization reaction mechanism was divided into four corresponding categories. This database was used to predict 12 putative STS genes from the edible fungi Flammulina velutipes. Finally, three FvSTSs were selected to experimentally characterize their functions. FvSTS03 predominantly produced Δ-cadinol and FvSTS08 synthesized β-barbatene as the main product; these findings were consistent with those of the functional prediction analysis. A product titer of 78.8 mg/L β-barbatene was achieved in Saccharomyces cerevisiae via metabolic engineering. Our study findings will help screen or design STSs from fungi with specific product profiles as functional elements for applications in synthetic biology.

Genome-Wide Identification, and In-Silico Expression Analysis of YABBY Gene Family in Response to Biotic and Abiotic Stresses in Potato (Solanum tuberosum)

YABBY is among the specific transcription factor (TF) gene family in plants and plays an important role in the development of the leaves and floral organs. Its specific roles include lateral organ development, the establishment of dorsoventral polarity, and response to abiotic stress. Potato is an important crop worldwide and YABBY genes are not still identified and characterized in potato. So, little has been known about YABBY genes in potato until now. This study was carried out to perform genome-wide analysis, which will provide an in-depth analysis about the role of YABBY genes in potato. There have been seven StYAB genes identified, which are found to be located on seven different chromosomes. Through multiple sequence analyses, it has been predicted that the YABBY domain was present in all seven genes while the C2-C2 domain was found to be absent only in StYAB2. With the help of cis-element analysis, the involvement of StYAB genes in light, stress developmental, and hormonal responsiveness has been found. Furthermore, expression analysis from RNA-seq data of different potato organs indicated that all StYAB genes have a role in the vegetative growth of the potato plant. In addition to this, RNA-seq data also identified StYAB3, StYAB5, and StYAB7 genes showing expression during cadmium, and drought stress, while StYAB6 was highly expressed during a viral attack. Moreover, during the attack of Phytophthora infestans on a potato plant StYAB3, StYAB5, StYAB6, and StYAB7 showed high expression. This study provides significant knowledge about the StYAB gene structures and functions, which can later be used for gene cloning, and functional analysis; this information may be utilized by molecular biologists and plant breeders for the development of new potato lines.

The Metagenomic Analysis of Viral Diversity in Colorado Potato Beetle Public NGS Data

The Colorado potato beetle (CPB) is one of the most serious insect pests due to its high ecological plasticity and ability to rapidly develop resistance to insecticides. The use of biological insecticides based on viruses is a promising approach to control insect pests, but the information on viruses which infect leaf feeding beetles is scarce. We performed a metagenomic analysis of 297 CPB genomic and transcriptomic samples from the public National Center for Biotechnology Information Sequence Read Archive (NCBI SRA) database. The reads that were not aligned to the reference genome were assembled with metaSPAdes, and 13314 selected contigs were analyzed with BLAST tools. The contigs and non-aligned reads were also analyzed with Kraken2 software. A total of 3137 virus-positive contigs were attributed to different viruses belonging to 6 types, 17 orders, and 32 families, matching over 97 viral species. The annotated sequences can be divided into several groups: those that are homologous to genetic sequences of insect viruses (Adintoviridae, Ascoviridae, Baculoviridae, Dicistroviridae, Chuviridae, Hytrosaviridae, Iflaviridae, Iridoviridae, Nimaviridae, Nudiviridae, Phasmaviridae, Picornaviridae, Polydnaviriformidae, Xinmoviridae etc.), plant viruses (Betaflexiviridae, Bromoviridae, Kitaviridae, Potyviridae), and endogenous retroviral elements (Retroviridae, Metaviridae). Additionally, the full-length genomes and near-full length genome sequences of several viruses were assembled. We also found sequences belonging to Bracoviriform viruses and, for the first time, experimentally validated the presence of bracoviral genetic fragments in the CPB genome. Our work represents the first attempt to discover the viral genetic material in CPB samples, and we hope that further studies will help to identify new viruses to extend the arsenal of biopesticides against CPB.

Chloroplast redox state changes mark cell-to-cell signaling in the hypersensitive response

Hypersensitive response (HR)-conferred resistance is associated with induction of programmed cell death and pathogen spread restriction in its proximity. The exact role of chloroplastic reactive oxygen species and its link with salicylic acid (SA) signaling in HR remain unexplained. To unravel this, we performed a detailed spatiotemporal analysis of chloroplast redox response in palisade mesophyll and upper epidermis to potato virus Y (PVY) infection in a resistant potato genotype and its transgenic counterpart with impaired SA accumulation and compromised resistance. Besides the cells close to the cell death zone, we detected individual cells with oxidized chloroplasts further from the cell death zone. These are rare in SA-deficient plants, suggesting their role in signaling for resistance. We confirmed that chloroplast redox changes play important roles in signaling for resistance, as blocking chloroplast redox changes affected spatial responses at the transcriptional level. Through spatiotemporal study of stromule induction after PVY infection, we show that stromules are induced by cell death and also as a response to PVY multiplication at the front of infection. Overall induction of stromules is attenuated in SA-deficient plants.

CRISPR/Cas9-mediated fine-tuning of miRNA expression in tetraploid potato

MicroRNAs (miRNAs) are small noncoding RNAs, which modulate the abundance and spatiotemporal accumulation of target mRNAs at transcriptional and post-transcriptional levels and through that play important roles in several biological processes in plants. Here we show that in polyploid species, CRISPR/Cas9 system can be used for fine-tuning of miRNA expression, which can have broader range of applications compared to knock-out mutants. We established the complete pipeline for CRISPR-Cas9-mediated modulation of miRNA expression in potato. It consists of (1) design and assembly of dual sgRNA CRISPR/Cas9 constructs, (2) transient transfection of protoplasts following fast and efficient screening by high resolution melting analysis to select functional sgRNAs, and (3) stable transformation of potato explants with functional sgRNAs and selection of regenerated transgenic lines with desired mutations and desired miRNA abundance based on sequencing and RT-qPCR. We show that miRNA-editing using dual sgRNA approach results in different types of mutations among transgenic lines but also in different alleles of the same plant, which are target site-dependent. The most frequent were short deletions, but we also detected 1-nt insertions (T or G), deletions between two sgRNAs and larger deletions. miRNA abundance correlates with the frequency and type of introduced mutations, as more extensive mutations in more alleles result in lower miRNA abundance. Interestingly, some mutated loci can generate alternative miRNAs, now novel targets were however predicted for those. In all transgenic lines with Cas9 expression, we detected mutations, suggesting high efficiency of Cas9-editing. We confirmed the miRNA-editing efficiency of our optimised approach in two different potato genotypes and three different loci.

Responses of pea plants to multiple antagonists are mediated by order of attack and phytohormone crosstalk

Plants are often attacked by multiple antagonists and traits of the attacking organisms and their order of arrival onto hosts may affect plant defences. However, few studies have assessed how multiple antagonists, and varying attack order, affect plant defence or nutrition. To address this, we assessed defensive and nutritional responses of Pisum sativum plants after attack by a vector herbivore (Acrythosiphon pisum), a nonvector herbivore (Sitona lineatus), and a pathogen (Pea enation mosaic virus, PEMV). We show viruliferous A. pisum induced several antipathogen plant defence signals, but these defences were inhibited by S. lineatus feeding on peas infected with PEMV. In contrast, S. lineatus feeding induced antiherbivore defence signals, and these plant defences were enhanced by PEMV. Sitona lineatus also increased abundance of plant amino acids, but only when they attacked after viruliferous A. pisum. Our results suggest that diverse communities of biotic antagonists alter defence and nutritional traits of plants through complex pathways that depend on the identity of attackers and their order of arrival onto hosts. Moreover, we show interactions among a group of biotic stressors can vary along a spectrum from antagonism to enhancement/synergism based on the identity and order of attackers, and these interactions are mediated by a multitude of phytohormone pathways.

Ménage à Trois: Unraveling the Mechanisms Regulating Plant-Microbe-Arthropod Interactions

Plant-microbe-arthropod (PMA) three-way interactions have important implications for plant health. However, our poor understanding of the underlying regulatory mechanisms hampers their biotechnological applications. To this end, we searched for potential common patterns in plant responses regarding taxonomic groups or lifestyles. We found that most signaling modules regulating two-way interactions also operate in three-way interactions. Furthermore, the relative contribution of signaling modules to the final plant response cannot be directly inferred from two-way interactions. Moreover, our analyses show that three-way interactions often result in the activation of additional pathways, as well as in changes in the speed or intensity of defense activation. Thus, detailed, basic knowledge of plant-microbe-arthropod regulation will be essential for the design of environmentally friendly crop management strategies.

Precision transcriptomics of viral foci reveals the spatial regulation of immune-signaling genes and identifies RBOHD as an important player in the incompatible interaction between potato virus Y and potato

Whereas the activation of resistance (R) proteins has been intensively studied, the downstream signaling mechanisms leading to the restriction of the pathogen remain mostly unknown. We studied the immunity network response conditioned by the potato Ny-1 gene against potato virus Y. We analyzed the processes in the cell death zone and surrounding tissue on the biochemical and gene expression levels in order to reveal the spatiotemporal regulation of the immune response. We show that the transcriptional response in the cell death zone and surrounding tissue is dependent on salicylic acid (SA). For some genes the spatiotemporal regulation is completely lost in the SA-deficient line, whereas other genes show a different response, indicating multiple connections between hormonal signaling modules. The induction of NADPH oxidase RBOHD expression occurs specifically on the lesion border during the resistance response. In plants with silenced RBOHD, the functionality of the resistance response is perturbed and the spread of the virus is not arrested at the site of infection. RBOHD is required for the spatial accumulation of SA, and conversely RBOHD is under the transcriptional regulation of SA. Using spatially resolved RNA-seq, we also identified spatial regulation of an UDP-glucosyltransferase, another component in feedback activation of SA biosynthesis, thus deciphering a novel aspect of resistance signaling.

Endophytic Bacillus spp. as a Prospective Biological Tool for Control of Viral Diseases and Non-vector Leptinotarsa decemlineata Say. in Solanum tuberosum L

Viral diseases and their damage causing significant loss to economically important crops have increased by several folds during the last decade. All the conventional approaches are not able to eradicate the viral infection. Therefore, there is a need to look for efficient and eco-friendly viral disease-preventive measures. The genomic material of the majority of deleterious viruses of higher plants is RNA. One of the possible measures to control viruses is the use of ribonucleases (RNases), which can cleave RNA in the viral genome. Based on this, we investigated the RNase activity of endophytic Bacillus spp., which can enrich in 10³–10⁵ colony-forming units per gram of wet mass of aboveground part of potato plants. A high level of RNase activity was observed in the culture medium of Bacillus thuringiensis B-6066, Bacillus sp. STL-7, Bacillus sp. TS2, and Bacillus subtilis 26D. B. thuringiensis B-5351 had low RNase activity but high ability to colonize internal plant tissues, Bacillus sp. STL-7 with high RNase activity have relatively low number of cells in internal tissues of plants. B. thuringiensis B-6066, B. subtilis 26D, and Bacillus sp. TS stimulate RNase activity in potato plants for a long time after application. Strains with high ability to colonize internal plant tissues combined with high RNase activity reduced severity of viral diseases symptoms on plants and reduced the incidence of potato viruses M, S, and Y. It is worth noting that Bacillus spp. under investigation reduced the number of Leptinotarsa decemlineata Say. egg clusters and larvae on treated plants and showed antifeedant activity. This results in increase of potato productivity mainly in the fraction of major tubers. B. subtilis 26D and Bacillus sp. TS2 combining endophytic lifestyle, RNase, and antifeedant activity may become the basis for the development of biocontrol agents for plant protection.

Aegerolysins from the fungal genus Pleurotus - Bioinsecticidal proteins with multiple potential applications

The aegerolysin proteins ostreolysin A6, pleurotolysin A2 and erylysin A are produced by mushrooms of the genus Pleurotus. These aegerolysins can interact specifically with sphingolipid-enriched membranes. In particular, they strongly bind insect cells and to artificial lipid membranes that contain physiologically relevant concentrations of the main invertebrate-specific sphingolipid, ceramide phosphoethanolamine. Moreover, the aegerolysins permeabilise these membranes when combined with their protein partner pleurotolysin B, which contains a membrane-attack-complex/perforin domain. These aegerolysin/ pleurotolysin B complexes show strong and selective toxicity towards western corn rootworm larvae and adults and Colorado potato beetle larvae. Their insecticidal activities arise through aegerolysin binding to ceramide phosphoethanolamine in the insect midgut. This mode of membrane binding is different from those described for similar aegerolysin-based complexes of bacterial origin (e.g., Cry34Ab1/Cry35Ab1), or other Bacillus thuringiensis proteinaceous crystal toxins, which associate with protein receptors. The ability of Pleurotus aegerolysins to specifically interact with sphingolipid-enriched domains in mammalian cells can be further exploited to visualize lipid rafts in living cells, and to treat certain types of tumours and metabolic disorders. Finally, these proteins can strongly enhance fruiting initiation of P. ostreatus even when applied externally. In this review, we summarise the current knowledge of the potential biotechnological and biomedical applications of the Pleurotus aegerolysins, either alone or when complexed with pleurotolysin B, with special emphasis on their bioinsecticidal effects.

Validating the Potential of Double-Stranded RNA Targeting Colorado Potato Beetle Mesh Gene in Laboratory and Field Trials

Colorado potato beetle (CPB) is an agricultural pest of solanaceous crops, notorious for its rapid resistance development to chemical pesticides. Foliar spraying of dsRNA formulations is a promising innovative technology providing highly specific and environmentally acceptable option for CPB management. We designed dsRNA to silence CPB mesh gene (dsMESH) and performed laboratory feeding trials to assess impacts on beetle survival and development. We compared the effectiveness of in vivo and in vitro produced dsRNA in a series of laboratory experiments. We additionally performed a field trial in which the efficacy of dsRNA sprayed onto potato foliage was compared to a spinosad-based insecticide. We showed that dsMESH ingestion consistently and significantly impaired larval growth and decreased larval survival in laboratory feeding experiments. In vivo produced dsRNA performed similarly as in vitro synthesized dsRNA in laboratory settings. In the field trial, dsMESH was as effective in controlling CPB larvae as a commercial spinosad insecticide, its activity was however slower. We discuss limitations and benefits of a potential dsMESH-based CPB management strategy and list some important RNAi based CPB research topics, which will have to be addressed in future.

Dynamic Transcriptional Profiles of Arabidopsis thaliana Infected by Tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) is a negative-stranded RNA virus that infects hundreds of plant species, causing great economic loss. Infected Arabidopsis thaliana plants develop symptoms including chlorosis and wilt, which can lead to cell death. From 9 to 15 days after TSWV infection, symptoms progress through a three-stage process of appearance, severity, and death. In this study, deep sequencing technology was first used to explore gene expression in response to TSWV infection in model plant A. thaliana at different symptom development stages. We found that plant immune defense and protein degradation are induced by TSWV infection and that both inductions became stronger over time. The photosynthesis pathway was attenuated with TSWV infection. Cell wall metabolism had a large extent of downregulation while some genes were upregulated. These results illustrate the dynamic nature of TSWV infection in A. thaliana at the whole-transcriptome level. The link between biological processes and subpathway metabolism was further analyzed. Our study provides new insight into host regulatory networks and dynamic processes in response to TSWV infection.

Assessing the Impact on Virus Transmission and Insect Vector Behavior of a Viral Mixed Infection in Melon

Mixed viral infections in plants are common, and can result in synergistic or antagonistic interactions. Except in complex diseases with severe symptoms, mixed infections frequently remain unnoticed, and their impact on insect vector transmission is largely unknown. In this study, we considered mixed infections of two unrelated viruses commonly found in melon plants, the crinivirus cucurbit yellow stunting disorder virus (CYSDV) and the potyvirus watermelon mosaic virus (WMV), and evaluated their vector transmission by whiteflies and aphids, respectively. Their dynamics of accumulation was analyzed until 60 days postinoculation (dpi) in mixed-infected plants, documenting reduced titers of WMV and much higher titers of CYSDV compared with single infections. At 24 dpi, corresponding to the peak of CYSDV accumulation, similar whitefly transmission rates were obtained when comparing either individual or mixed-infected plants as CYSDV sources, although its secondary dissemination was slightly biased toward plants previously infected with WMV, regardless of the source plant. However, at later time points, mixed-infected plants partially recovered from the initially severe symptoms, and CYSDV transmission became significantly higher. Interestingly, aphid transmission rates both at early and late time points were unaltered when WMV was acquired from mixed-infected plants despite its reduced accumulation. This lack of correlation between WMV accumulation and transmission could result from compensatory effects observed in the analysis of the aphid feeding behavior by electrical penetration graphs. Thus, our results showed that mixed-infected plants could provide advantages for both viruses, directly favoring CYSDV dissemination while maintaining WMV transmission.

Virus-Dependent and -Independent Responses of Sitobion avenae (Homoptera: Aphididae) Feeding on Wheat Infected by Transmitted and Nontransmitted Viruses at Transcriptomic Level

Most plant viruses maintain complex interactions with their vector or nonvector insects and can indirectly (via host plants) or directly affect the fitness of insects. However, little is known about the genes involved in the interactions between insects and transmitted or nontransmitted viruses, particularly nontransmitted viruses. Sitobion avenae (Fabricius) is a vector of barley yellow dwarf virus GAV strains (BYDV-GAV), but not a vector of wheat dwarf virus (WDV), which is transmitted by the leafhopper [Psammotettix alienus (Dahlbom)]. In this study, S. avenae was utilized to determine the transcriptomic responses after feeding on wheat infected by each of the two viruses, respectively, using an Illumina Hiseq sequencing platform. The transcriptomic data presented 61,508 genes, of which 854 differentially expressed. Moreover, in addition to sharing 208 genes, the number of differentially expressed genes (DEGs) in S. avenae exposed to BYDV was higher (800) than that when exposed to WDV (262). The DEGs related to the immune system and fitness of S. avenae in response to BYDV-/WDV-infected plants were identified and analyzed using Gene Ontologies (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG), and the number of related DEGs was lower as nonvector than as vector. This study provides the baseline information to further examine molecular mechanisms of how wheat viruses affect S. avenae fitness and immune response either as a vector for BYDV-GAV or as a nonvector for WDV.

Bacillus amyloliquefaciens strain MBI600 induces salicylic acid dependent resistance in tomato plants against Tomato spotted wilt virus and Potato virus Y

Plant growth promoting rhizobacteria have been proposed as effective biocontrol agents against several fungal and bacterial plant pathogens. However, there is limited knowledge regarding their effect against viruses. In this study, Bacillus amyloliquefaciens strain MBI600 (MBI600), active ingredient of the biological fungicide Serifel® (BASF SE), was tested for its antiviral action in tomato plants. Drench, foliar or soil amendment applications of MBI600 reduced up to 80% the incidence of Tomato spotted wilt virus under two different sets of environmental conditions. In addition, drench application of MBI600 delayed Potato virus Y systemic accumulation. Transcriptional analysis of a range of genes associated with salicylic acid (SA)- or jasmonic acid - related defense, priming or basal defense against viruses, revealed the induction of the SA signaling pathway in tomato after MBI600 treatment, and discrete gene expression patterns in plant response to TSWV and PVY infection.

Sugarcane Mosaic Virus-Based Gene Silencing in Nicotiana benthamiana

Background: Potyvirus-based virus-induced gene silencing (VIGS) is used for knocking down the expression of a target gene in numerous plant species. Sugarcane mosaic virus (SCMV) is a monopartite, positive single strand RNA virus. Objectives: pBINTRA6 vector was modifi ed by inserting a gene segment of SCMV in place of Tobacco rattle virus (TRV) genome part 1 (TRV1 or RNA1) and the two nonstructural proteins of TRV2(RNA2). Materials and Methods: SCMV construct was inoculated into 3-4 weeks Nicotiana benthamiana plant leaves either by using a needleless syringe or applying pricking with a toothpick. Results: The construct (SCMV-RNA2) successfully induced post-transcriptional gene silencing (PTGS) of the target genes GFP and ChlI through agroinoculation proving that SCMV is a substitute of the RNA1, which plays a pivotal role in the systemic gene silencing. 2-3-weeks of post inoculation, target genes' silencing was observed in the newly developed noninoculated leaves. Conclusions: The newly developed construct expresses the knocked down of the endogenous as well as exogenous genes and only four weeks are required for the transient expression of the gene silencing based on SCMV-VIGS system.

Engineering resistance to virus transmission

Engineering plants for resistance to virus transmission by invertebrate vectors has lagged behind other forms of plant protection. Vectors typically transmit more than one virus. Thus, vector resistance could provide a wider range of protection than defenses directed solely against one virus or virus group. We discuss current knowledge of vector-host-virus interactions, the roles of viral gene products in host and vector manipulation, and the effects of semiochemicals on host-vector interactions, and how this knowledge could be employed to disrupt transmission dynamics. We also discuss how resistance to vectors could be generated through genetic engineering or gene editing or indirectly through use of biocontrol using plant-resident viruses that infect vectors.

Herbivore Oral Secreted Bacteria Trigger Distinct Defense Responses in Preferred and Non-Preferred Host Plants

Insect symbiotic bacteria affect host physiology and mediate plant-insect interactions, yet there are few clear examples of symbiotic bacteria regulating defense responses in different host plants. We hypothesized that plants would induce distinct defense responses to herbivore- associated bacteria. We evaluated whether preferred hosts (horsenettle) or non-preferred hosts (tomato) respond similarly to oral secretions (OS) from the false potato beetle (FPB, Leptinotarsa juncta), and whether the induced defense triggered by OS was due to the presence of symbiotic bacteria in OS. Both horsenettle and tomato damaged by antibiotic (AB) treated larvae showed higher polyphenol oxidase (PPO) activity than those damaged by non-AB treated larvae. In addition, application of OS from AB treated larvae induced higher PPO activity compared with OS from non-AB treated larvae or water treatment. False potato beetles harbor bacteria that may provide abundant cues that can be recognized by plants and thus mediate corresponding defense responses. Among all tested bacterial isolates, the genera Pantoea, Acinetobacter, Enterobacter, and Serratia were found to suppress PPO activity in tomato, while only Pantoea sp. among these four isolates was observed to suppress PPO activity in horsenettle. The distinct PPO suppression caused by symbiotic bacteria in different plants was similar to the pattern of induced defense-related gene expression. Pantoea inoculated FPB suppressed JA-responsive genes and triggered a SA-responsive gene in both tomato and horsenettle. However, Enterobacter inoculated FPB eliminated JA-regulated gene expression and elevated SA-regulated gene expression in tomato, but did not show evident effects on the expression levels of horsenettle defense-related genes. These results indicate that suppression of plant defenses by the bacteria found in the oral secretions of herbivores may be a more widespread phenomenon than previously indicated.

Antagonistic within-host interactions between plant viruses: molecular basis and impact on viral and host fitness

Double infections of related or unrelated viruses frequently occur in single plants, the viral agents being inoculated into the host plant simultaneously (co-infection) or sequentially (super-infection). Plants attacked by viruses activate sophisticated defence pathways which operate at different levels, often at significant fitness costs, resulting in yield reduction in crop plants. The occurrence and severity of the negative effects depend on the type of within-host interaction between the infecting viruses. Unrelated viruses generally interact with each other in a synergistic manner, whereas interactions between related viruses are mostly antagonistic. These can incur substantial fitness costs to one or both of the competitors. A relatively well-known antagonistic interaction is cross-protection, also referred to as super-infection exclusion. This type of interaction occurs when a previous infection with one virus prevents or interferes with subsequent infection by a homologous second virus. The current knowledge on why and how one virus variant excludes or restricts another is scant. Super-infection exclusion between viruses has predominantly been attributed to the induction of RNA silencing, which is a major antiviral defence mechanism in plants. There are, however, presumptions that various mechanisms are involved in this phenomenon. This review outlines the current state of knowledge concerning the molecular mechanisms behind antagonistic interactions between plant viruses. Harmful or beneficial effects of these interactions on viral and host plant fitness are also characterized. Moreover, the review briefly outlines the past and present attempts to utilize antagonistic interactions among viruses to protect crop plants against destructive diseases.

RNA-dependent RNA polymerase 1 in potato (Solanum tuberosum) and its relationship to other plant RNA-dependent RNA polymerases

Cellular RNA-dependent RNA polymerases (RDRs) catalyze synthesis of double-stranded RNAs that can serve to initiate or amplify RNA silencing. Arabidopsis thaliana has six RDR genes; RDRs 1, 2 and 6 have roles in anti-viral RNA silencing. RDR6 is constitutively expressed but RDR1 expression is elevated following plant treatment with defensive phytohormones. RDR1 also contributes to basal virus resistance. RDR1 has been studied in several species including A. thaliana, tobacco (Nicotiana tabacum), N. benthamiana, N. attenuata and tomato (Solanum lycopersicum) but not to our knowledge in potato (S. tuberosum). StRDR1 was identified and shown to be salicylic acid-responsive. StRDR1 transcript accumulation decreased in transgenic potato plants constitutively expressing a hairpin construct and these plants were challenged with three viruses: potato virus Y, potato virus X, and tobacco mosaic virus. Suppression of StRDR1 gene expression did not increase the susceptibility of potato to these viruses. Phylogenetic analysis of RDR genes present in potato and in a range of other plant species identified a new RDR gene family, not present in potato and found only in Rosids (but apparently lost in the Rosid A. thaliana) for which we propose the name RDR7.

Tomato yellow leaf curl virus differentially influences plant defence responses to a vector and a non-vector herbivore

Plants frequently engage in simultaneous interactions with diverse classes of biotic antagonists. Differential induction of plant defence pathways by these antagonists, and interactions between pathways, can have important ecological implications; however, these effects are currently not well understood. We explored how Tomato yellow leaf curl virus (TYLCV) influenced the performance of its vector (Bemisia tabaci) and a non-vector herbivore (Tetranychus urticae) occurring separately or together on tomato plants (Solanum lycopersicum). TYLCV enhanced the performance of B. tabaci, although this effect was statistically significant only in the absence of T. urticae, which adversely affected B. tabaci performance regardless of infection status. In contrast, the performance of T. urticae was enhanced (only) by the combined presence of TYLCV and B. tabaci. Analyses of phytohormone levels and defence gene expression in wild-type tomatoes and various plant-defence mutants indicate that the enhancement of herbivore performance (for each species) entails the disruption of downstream defences in the jasmonic acid (JA) pathway. For T. urticae, this disruption appears to involve antagonistic effects of salicylic acid (SA), which is cumulatively induced to high levels by B. tabaci and TYLCV. In contrast, TYLCV was found to suppress JA-mediated responses to B. tabaci via mechanisms independent of SA.

Primary Metabolism, Phenylpropanoids and Antioxidant Pathways Are Regulated in Potato as a Response to Potato virus Y Infection

Potato production is one of the most important agricultural sectors, and it is challenged by various detrimental factors, including virus infections. To control losses in potato production, knowledge about the virus—plant interactions is crucial. Here, we investigated the molecular processes in potato plants as a result of Potato virus Y (PVY) infection, the most economically important potato viral pathogen. We performed an integrative study that links changes in the metabolome and gene expression in potato leaves inoculated with the mild PVY^N and aggressive PVY^NTN isolates, for different times through disease development. At the beginning of infection (1 day post-inoculation), virus-infected plants showed an initial decrease in the concentrations of metabolites connected to sugar and amino-acid metabolism, the TCA cycle, the GABA shunt, ROS scavangers, and phenylpropanoids, relative to the control plants. A pronounced increase in those metabolites was detected at the start of the strong viral multiplication in infected leaves. The alterations in these metabolic pathways were also seen at the gene expression level, as analysed by quantitative PCR. In addition, the systemic response in the metabolome to PVY infection was analysed. Systemic leaves showed a less-pronounced response with fewer metabolites altered, while phenylpropanoid-associated metabolites were strongly accumulated. There was a more rapid onset of accumulation of ROS scavengers in leaves inoculated with PVY^N than those inoculated with PVY^NTN. This appears to be related to the lower damage observed for leaves of potato infected with the milder PVY^N strain, and at least partially explains the differences between the phenotypes observed.