Plum Pox Research Articles

Molecular Plant-Plum Pox Virus Interactions.

Plum pox virus, the agent that causes sharka disease, is among the most important plant viral pathogens, affecting Prunus trees across the globe. The fabric of interactions that the virus is able to establish with the plant regulates its life cycle, including RNA uncoating, translation, replication, virion assembly, and movement. In addition, plant-virus interactions are strongly conditioned by host specificities, which determine infection outcomes, including resistance. This review attempts to summarize the latest knowledge regarding Plum pox virus-host interactions, giving a comprehensive overview of their relevance for viral infection and plant survival, including the latest advances in genetic engineering of resistant species.

Translatome Profiling of Plum Pox Virus-Infected Leaves in European Plum Reveals Temporal and Spatial Coordination of Defense Responses in Phloem Tissues.

Plum pox virus (PPV) is the causative agent of sharka, a devastating disease of stone fruits including peaches, apricots, and plums. PPV infection levels and associated disease symptoms can vary greatly, depending upon the virus strain, host species, or cultivar as well as developmental age of the infected tissues. For example, peaches often exhibit mild symptoms in leaves and fruit while European plums typically display severe chlorotic rings. Systemic virus spread into all host tissues occurs via the phloem, a process that is poorly understood in perennial plant species that undergo a period of dormancy and must annually renew phloem tissues. Currently, little is known about how phloem tissues respond to virus infection. Here, we used translating ribosome affinity purification followed by RNA sequencing to identify phloem- and nonphloem-specific gene responses to PPV infection during leaf development in European plum (Prunus domestica L.). Results showed that, during secondary leaf morphogenesis (4- and 6-week-old leaves), the phloem had a disproportionate response to PPV infection with two- to sixfold more differentially expressed genes (DEGs) in phloem than nonphloem tissues, despite similar levels of viral transcripts. In contrast, in mature 12-week-old leaves, virus transcript levels dropped significantly in phloem tissues but not in nonphloem tissues. This drop in virus transcripts correlated with an 18-fold drop in phloem-specific DEGs. Furthermore, genes associated with defense responses including RNA silencing were spatially coordinated in response to PPV accumulation and were specifically induced in phloem tissues at 4 to 6 weeks. Combined, these findings highlight the temporal and spatial dynamics of leaf tissue responses to virus infection and reveal the importance of phloem responses within a perennial host.

Silencing of one copy of the translation initiation factor eIFiso4G in Japanese plum (Prunus salicina) impacts susceptibility to Plum pox virus (PPV) and small RNA production

BackgroundIn plants, host factors encoded by susceptibility (S) genes are indispensable for viral infection. Resistance is achieved through the impairment or the absence of those susceptibility factors. Many S genes have been cloned from model and crop species and a majority of them are coding for members of the eukaryotic translation initiation complex, mainly eIF4E, eIF4G and their isoforms. The aim of this study was to investigate the role of those translation initiation factors in susceptibility of stone fruit species to sharka, a viral disease due to Plum pox virus (PPV).ResultsFor this purpose, hairpin-inducing silencing constructs based on Prunus persica orthologs were used to generate Prunus salicina (Japanese plum) 4E and 4G silenced plants by Agrobacterium tumefaciens-mediated transformation and challenged with PPV. While down-regulated eIFiso4E transgenic Japanese plums were not regenerated in our conditions, eIFiso4G11-, but not the eIFiso4G10-, silenced plants displayed durable and stable resistance to PPV. We also investigated the alteration of the si- and mi-RNA profiles in transgenic and wild-type Japanese plums upon PPV infection and confirmed that the newly generated small interfering (si) RNAs, which are derived from the engineered inverted repeat construct, are the major contributor of resistance to sharka.ConclusionsOur results indicate that S gene function of the translation initiation complex isoform is conserved in Prunus species. We discuss the possibilities of using RNAi silencing or loss-of-function mutations of the different isoforms of proteins involved in this complex to breed for resistance to sharka in fruit trees.

Quantitative analysis of the interaction of heterologous viruses with Plum pox virus in C5 HoneySweet transgenic plums

Stone fruits are an important crop in most parts of the world and are heavily challenged by several viruses including Plum pox virus (PPV), Prune dwarf virus (PDV), Prunus necrotic ringspot virus (PNRSV), and Apple chlorotic leaf spot virus (ACLSV). We validated the PPV resistance in C5 plum plants (commercially known as HoneySweet) grown in the Czech Republic for more than 16 years in a field trial experiment under natural environmental conditions. We quantified single (PPV-Rec) and mixed viruses (PPV-Rec+ACLSV, PPV-Rec+PDV and PPV-Rec+ACLSV+PDV) in C5 transgenic plums inoculated for the period 2016 to 2018. The accumulation of PPV-Rec was high (∼5.43E+05 copies) compared with that of ACLSV (∼8.70E+04 copies) in the inoculated graft of C5 transgenic plants. Leaves close to the inoculum sources showed a differential level of virus titre in single and mixed infections (∼10 to ∼5×102 copies). C5 plants with permanent virus pressure showed 103- to 105-fold fewer copies of viruses than those of the inoculated graft. We observed high accumulation of conserved miRNAs such as miR167, miR69 and miR396 in C5 plants co-infected with PPV, ACLSV and PDV that are associated with its resistance against viruses. Overall, i) C5 transgenic plums showed high resistance to PPV infection, and a low level (∼32 copies) of PPV only accumulated in some grafted plants, ii) high accumulation of PPV was found in inoculated grafts in single PPV infection and mixed infections, iii) heterologous virus infection sustained by ACLSV or PDV did not suppress PPV resistance, and iv) high and low conserved microRNAs accumulated in C5 plants.

Breeding for Plum pox virus resistant rootstocks by interspecific hybridization of Prunus species – state of the art and preliminary results of rootstock trials

Breeding for <i>Plum pox virus</i> resistant rootstocks by interspecific hybridization of <i>Prunus</i> species – state of the art and preliminary results of rootstock trials

The effect of new rootstocks with hypersensitivity resistance to Plum pox virus ‘Docera 6’ and ‘Dospina 235’ on the growth and yield of young plum trees

The effect of new rootstocks with hypersensitivity resistance to <i>Plum pox virus</i> ‘Docera 6’ and ‘Dospina 235’ on the growth and yield of young plum trees

The effectiveness of hypersensitivity resistance of Prunus domestica ‘Jojo’ and P. domestica × P. cerasifera ‘Docera® 6’ against a broad range of Plum pox virus isolates

The effectiveness of hypersensitivity resistance of <i>Prunus domestica</i> ‘Jojo’ and <i>P. domestica</i> × <i>P. cerasifera</i> ‘Docera^® 6’ against a broad range of <i>Plum pox virus</i> isolates

First Report of Plum pox virus Strain W in Kazakhstan, on Prunus domestica

First Report of <i>Plum pox virus</i> Strain W in Kazakhstan, on <i>Prunus domestica</i>

Molecular characterization of a novel potyvirus infecting noni.

The complete genomic sequence of a novel potyvirus from a noni plant in China (Morinda citrifolia) with foliar mosaic and chlorotic symptoms was determined. The genomic RNA consists of 9645 nucleotides (nt) excluding the poly(A) tail, containing the typical open reading frame (ORF) of potyviruses and encoding a large putative polyprotein of 3077 amino acids (aa). Pairwise comparisons showed that the virus shares 48.8%-58.5% sequence identity at the genome sequence level, and 38.5%-53.4% identity at the polyprotein sequence level with other members of the genus Potyvirus. Phylogenetic analysis indicated that the virus is most closely related to jasmine virus T and plum pox virus in the genus Potyvirus. These results suggest that this virus should be considered a distinct member of the genus Potyvirus, and it was tentatively named "noni mosaic virus" (NoMV).

First Report of Plum Pox Virus Strains M, D, and Rec Infecting Prunus spp. in the Republic of North Macedonia

First Report of Plum Pox Virus Strains M, D, and Rec Infecting <i>Prunus</i> spp. in the Republic of North Macedonia

The global phylogeny of Plum pox virus is emerging.

The 206 complete genomic sequences of Plum pox virus in GenBank (January 2019) were downloaded. Their main open reading frames (ORF)s were compared by phylogenetic and population genetic methods. All fell into the nine previously recognized strain clusters; the PPV-Rec and PPV-T strain ORFs were all recombinants, whereas most of those in the PPV-C, PPV-CR, PPV-CV, PPV-D, PPV-EA, PPV-M and PPV-W strain clusters were not. The strain clusters ranged in size from 2 (PPV-CV and PPV-EA) to 74 (PPV-D). The isolates of eight of the nine strains came solely from Europe and the Levant (with an exception resulting from a quarantine breach), but many PPV-D strain isolates also came from east and south Asia and the Americas. The estimated time to the most recent common ancestor (TMRCA) of all 134 non-recombinant ORFs was 820 (865-775) BCE. Most strain populations were only a few decades old, and had small intra-strain, but large inter-strain, differences; strain PPV-W was the oldest. Eurasia is clearly the 'centre of emergence' of PPV and the several PPV-D strain populations found elsewhere only show evidence of gene flow with Europe, so have come from separate introductions from Europe. All ORFs and their individual genes show evidence of strong negative selection, except the positively selected pipo gene of the recently migrant populations. The possible ancient origins of PPV are discussed.

Sterol isomerase HYDRA1 interacts with RNA silencing suppressor P1b and restricts potyviral infection.

Plants use RNA silencing as a strong defensive barrier against virus challenges, and viruses counteract this defence by using RNA silencing suppressors (RSSs). With the objective of identifying host factors helping either the plant or the virus in this interaction, we have performed a yeast two-hybrid screen using P1b, the RSS protein of the ipomovirus Cucumber vein yellowing virus (CVYV, family Potyviridae), as a bait. The C-8 sterol isomerase HYDRA1 (HYD1), an enzyme involved in isoprenoid biosynthesis and cell membrane biology, and required for RNA silencing, was isolated in this screen. The interaction between CVYV P1b and HYD1 was confirmed in planta by Bimolecular Fluorescence Complementation assays. We demonstrated that HYD1 negatively impacts the accumulation of CVYV P1b in an agroinfiltration assay. Moreover, expression of HYD1 inhibited the infection of the potyvirus Plum pox virus, especially when antiviral RNA silencing was boosted by high temperature or by coexpression of homologous sequences. Our results reinforce previous evidence highlighting the relevance of particular composition and structure of cellular membranes for RNA silencing and viral infection. We report a new interaction of an RSS protein from the Potyviridae family with a member of the isoprenoid biosynthetic pathway.

Susceptibility of SEO/‘Harlayne’ type resistant apricot cultivars to PPV-T

Plum pox virus (PPV) is one of the most detrimental diseases of the Prunus species. The use of genetic resistance is the most promising solution for the control of the virus. To date, in apricot the resistance has only been found in the North American germplasm. The American cultivars ‘Stark Early Orange’ (SEO), ‘Goldrich’, ‘Harlayne’, ‘Stella’, and ‘Harcot’ are known as resistant against to PPV-D and M strain, both of which are the most common strains in Europe. These cultivars host a major locus located on the Linkage Group One (LG1) accounting for 70% of PPV resistance. In a previous study, Turkish apricot germplasm was screened for three markers which are known to be linked to the resistance locus on LG1 and five accessions in the Turkish collection were identified to host the markers. Here we report the first two years results of the biological test applied to the same collection. Biological test was commenced in Kayseri in 2012 by graft inoculating the accession with a PPV-T (Turkey) strain. After examinations in two consecutive years, we observed that SEO, ‘Harlayne’, ‘Harcot’ and the five accessions of Turkish apricot germplasm with resistance markers fail to show resistance to PPV-T. However, in the third year of observation the symptom level decreased on the resistant accessions.

Genetic engineering of PPV resistance in plum rootstock ‘Elita’: an initial study

The present study describes an Agrobacterium-mediated transformation protocol for plum rootstock 'Elita' ((Prunus pumila L. × P. salicina Lindl.) × (P. cerasifera Ehrh.)) using leaf explants. The system enables an efficient plant regeneration with the retention of the traits of the original rootstock. The transformation experiments were conducted using a genetic construct containing the self-complementary sequences of a fragment of PPV-CP gene separated by an intron for inducing Plum pox virus (PPV) resistance through the mechanism of post-transcriptional gene silencing. Transgenic plum plants' rootstocks were produced from organogenic callus developed from leaf explants through a 6-month period culture after inoculation. PCR-analysis confirmed the transgenic status of the produced plants by amplification of the fragments of “hairpin”-PPV-CP construct and hpt gene. To our knowledge, this is the first report of a successful attempt to produce transgenic plum rootstock.

Does Genetic Engineering Influence the Nutritional Value of Plums? Case Study on Two conventional and One Genetically Engineered Plum Fruits

Plums are low-calorie fruits with a low glycaemic index score. Prunus domestica L. is one of the tree fruits threatened by Plum pox potyvirus (PPV), a quarantine disease that causes fruit loss to plums and other stone fruits. HoneySweet is a plum tree created to be resistant to this virus. Beside genetical determinations, chemical composition and nutritional value are important for a future acceptance in the cultivation of this type of fruit trees. Two conventional (Renclod Althan and Stanley) and one genetically engineered (HoneySweet) plum fruits were evaluated for the nutritional value determination. The analyzed samples showed nutritionally valuable features. HoneySweet variety had a balanced content of individual carbohydrates. The total lipid content had values quite close to the HoneySweet and Stanley varieties, far superior to Renclod Althan variety. HoneySweet transgenic plum had the highest total protein content. Also, HoneySweet variety is distinguished by a balanced protein and lipid content. By comparing the three analyzed varieties from the perspective of the most important physic-chemical nutrients (carbohydrates, proteins and lipids), the highest nutritional value was registered in Stanley variety, closely followed by HoneySweet, and then by Reine Claude d’Althan.

Improving Management Strategies of Plant Diseases Using Sequential Sensitivity Analyses.

Improvement of management strategies of epidemics is often hampered by constraints on experiments at large spatiotemporal scales. A promising approach consists of modeling the biological epidemic process and human interventions, which both impact disease spread. However, few methods enable the simultaneous optimization of the numerous parameters of sophisticated control strategies. To do so, we propose a heuristic approach (i.e., a practical improvement method approximating an optimal solution) based on sequential sensitivity analyses. In addition, we use an economic improvement criterion based on the net present value, accounting for both the cost of the different control measures and the benefit generated by disease suppression. This work is motivated by sharka (caused by Plum pox virus), a vector-borne disease of prunus trees (especially apricot, peach, and plum), the management of which in orchards is mainly based on surveillance and tree removal. We identified the key parameters of a spatiotemporal model simulating sharka spread and control and approximated optimal values for these parameters. The results indicate that the current French management of sharka efficiently controls the disease, but it can be economically improved using alternative strategies that are identified and discussed. The general approach should help policy makers to design sustainable and cost-effective strategies for disease management.

Plum Germplasm Resources and Breeding in Romania

Abstract In Romania, work on identification, conservation and evaluation of fruit genetic resources activities was initiated in 1970 in order to limit the loss of biodiversity. There are rich sources of germplasm located in two research centres: RIFG Pitesti with 642 accessions and UCv-SCDP Vâlcea with 361 accessions, representing wild species, local populations, named cultivars, breeder’s selections and rootstocks. Observations were made according to the IBPGR Prunus descriptors updated by the ECP/GR Prunus Working Group. The following genetic resources from the Piteşti and Vâlcea collections were used in a breeding programme in the development of several plum cultivars: ‘Grase de Becs’, ‘Carpatin’, ‘Ialomiža’, ‘Kirke’, ‘Wilhelmina Späth’ (for resistance / tolerance to Plum pox virus); ‘Vinete romāneşti’, ‘Tuleu timpuriu’, ‘Anna Späth’ (for late blooming), ‘Tuleu gras’, ‘Vâlcean’ (for fruit quality), ‘Stanley’, ‘Pescăruş’, ‘Centenar’ (for productivity), and ‘Diana’ (for self-fertility). The plum rootstock breeding programme used the following genotypes as sources of genes: ‘Rosior văratec’, ‘Brompton’, ‘Renclod Verde’, ‘Pixy’, ‘Saint Julien A’, ‘Albe mici’, ‘Scolduş’, ‘Porumbar’, etc. Breeding using the germplasm in these collections resulted in the release of 40 cultivars and 11 generative and vegetative rootstocks.

Update on Distribution and Genetic Variability of Plum pox virus Strains in Bulgaria

Field surveys for Plum pox virus (PPV) infection were conducted in stone fruit orchards all over Bulgaria. In total, 1168 out of 3020 leaf samples from cultivated Prunus spp. and wildly growing P. cerasifera trees reacted positive for PPV in DASI-ELISA with the universal monoclonal antibody (MAb) 5B. Further ELISA analyses showed that 987 and 127 isolates belonged to PPV-M and PPV-D serotypes, respectively. The plum and P. cerasifera showed 82.0% and 50.5% levels of infection, respectively followed by the peach (40.0%) and the apricot (32.0%). Five hundred fifty one PPV isolates were further typed by IC-RT-PCR with PPV-Rec, -M and -D-specific primers, targeting (Cter)NIb-(Nter) CP genome region, as 125 isolates were sequenced. The results revealed the presence of PPV-Rec, PPV-M and PPV-D and mixed infections of these strains. PPV-Rec was the most prevalent strain (49.0%), followed by PPV-M (40.1%), while PPV-D was the less spread strain (8.2%). PPV-Rec was the most common strain in plums, including the eight “old-aged” trees from the region of the first Sharka discovery. PPV-M was the most prevalent strain in peach and apricot. Phylogenetic analyses on (Cter)NIb-(Nter)CP of the isolates were performed. PPV-Rec isolates formed a homogeneous group, while PPV-M isolates split into PPV-Ma and PPV-Mb subgroups. Five separated clades were formed by the analyzed PPV-D isolates. Nucleotide sequences of the partial CP coding region of the analyzed isolates revealed a slightly higher intra-strain genetic variability in PPV-Rec and PPV-M isolates, while that of PPV-D strain isolates was higher from the reported for these strains.

Approved genetically modified (GM) horticultural plants: A 25-year perspective

Abstract In this review, we present genetically modified (GM) horticultural events that have passed the regulatory process and have been approved for cultivation or food use in different countries. The first authorization or deregulation of a GM horticultural plant issued 25 years ago initiated a fast expansion of GM organisms (GMO) engineered by using gene transfer technology. The list of GM horticultural species comprises representatives of vegetables, fruit plants and ornamentals. We describe their unique characteristics, often not achievable by conventional breeding, and how they were developed, and the approval process. Information on the adoption of GM horticultural cultivars and sale is accessed if commercialization has occurred. The review comprises, among others, Flavr SavrTM and other tomato cultivars with delayed ripening and improved shelf-life, insect-resistant eggplant (or brinjal), as well as virus-resistant squash, melon and the common bean, and also fruit trees, plum and papaya. Cultivation of the latter was particularly valuable to farmers in Hawaii as it ensured restoration of papaya production devastated earlier by the Papaya ringspot virus (PRSV). In contrast, a plum resistant to sharka (Plum pox virus; PPV) deregulated in the USA is still awaiting commercialization. GM events with improved quality include the recently marketed non-browning apple and high-lycopene pineapple. We also present orange petunia, blue ‘Applause’ rose and Moon-series carnations with a modified purple and violet flower colour. Finally, we discuss prospects of GM horticultural plants, including their development using promising new breeding technologies relying on genome editing and considered as an alternative to the transgenic approach.

Molecular and biological assessment reveals sources of resistance to Plum pox virus - Turkey strain in Turkish apricot (Prunus armeniaca) germplasm

Plum pox virus (PPV) is an important threat to apricot (Prunus armeniaca) production globally, including in Turkey and Iran, the world's leading producers of dried apricots. Although most apricot cultivars are susceptible and host resistance is the most promising approach to managing the disease. A few cultivars carrying the resistance locus PPVres have been used in breeding programs. Additional sources of resistance are highly desirable. The PPV susceptibility of cultivars in the Irano-Caucasian eco-geographical group, considered a secondary center of apricot diversity, has been little studied. We surveyed the response of 227 apricot accessions to PPV strain ‘Turkey’ (PPV-T) and, in parallel, scored molecular markers linked to PPVres. Four accessions (‘Cebir’, ‘Lifos’, ‘Karum’, and ‘Zard’) were identified as resistant to PPV-T and carried molecular markers for PPVres. Two additional accessions (‘Kaniş’, and Italian Cultivar ‘Fracasso’) were resistant but did not carry any of the PPVres resistance markers, indicating possible new sources of resistance. Their novelty was also supported by previously published molecular diversity analyses. The new resistance sources will be particularly useful for breeding new cultivars of apricot for drying. The marker ZP002 is more reliable and easy to use in selecting for the resistance allele at the PPVres locus. PPV resistance in apricot is not likely strain-specific.