Powdery mildew caused by Erysiphe corylacearum: An emerging problem on hazelnut in Italy.

Erysiphe corylacearum has recently been reported in northern Italy (Piedmont) and other European countries as the causal agent of a new emerging powdery mildew on hazelnut. This disease is much more dangerous than the common hazelnut powdery mildew caused by Phyllactinia guttata as it significantly reduces yield and quality of hazelnuts. This study aimed to perform morphological and molecular characterization of the fungal isolates from powdery mildew-infected plants in the Piedmont Italian region. Additionally, genetic diversity studies and pathogenicity tests were conducted. Thirty-six fungal isolates originating from symptomatic hazelnut plants exhibiting specific powdery mildew symptoms on the superior leaf side were identified morphologically as E. corylacearum. Single- and multilocus sequence typing of five loci (ITS, rpb2, CaM, GAPDH and GS) assigned all isolates as E. corylacearum. Multilocus and GAPDH phylogenetic studies resulted in the most efficient characterization of E. corylacearum. Studied fungal isolates were able to cause new emerging powdery mildew disease by fulfilling Koch's postulates. The emergence of powdery mildew disease in Italy revealed the E. corylacearum subgrouping, population expansion, and high nucleotide similarity with other recently identified E. corylacearum hazelnut isolates. To contain this harmful disease and inhibit the fungus spread into new geographical zones, it will be necessary to implement more rigorous monitoring in neighboring hazelnut plantations near infected hazelnuts, use sustainable fungicides and search for new biocontrol agents.

Exogenous Application of dsRNA for Protection against Tomato Leaf Curl New Delhi Virus.

Tomato leaf curl New Delhi virus (ToLCNDV) is an emerging plant pathogen, fast spreading in Asian and Mediterranean regions, and is considered the most harmful geminivirus of cucurbits in the Mediterranean. ToLCNDV infects several plant and crop species from a range of families, including Solanaceae, Cucurbitaceae, Fabaceae, Malvaceae and Euphorbiaceae. Up to now, protection from ToLCNDV infection has been achieved mainly by RNAi-mediated transgenic resistance, and non-transgenic fast-developing approaches are an urgent need. Plant protection by the delivery of dsRNAs homologous to a pathogen target sequence is an RNA interference-based biotechnological approach that avoids cultivating transgenic plants and has been already shown effective against RNA viruses and viroids. However, the efficacy of this approach against DNA viruses, particularly Geminiviridae family, is still under study. Here, the protection induced by exogenous application of a chimeric dsRNA targeting all the coding regions of the ToLCNDV DNA-A was evaluated in zucchini, an important crop strongly affected by this virus. A reduction in the number of infected plants and a delay in symptoms appearance, associated with a tendency of reduction in the viral titer, was observed in the plants treated with the chimeric dsRNA, indicating that the treatment is effective against geminiviruses but requires further optimization. Limits of RNAi-based vaccinations against geminiviruses and possible causes are discussed.

Raman-dielectrophoresis goes viral: towards a rapid and label-free platform for plant virus characterization.

An innovative spectroscopic method that allows to chemically and structurally characterize viruses directly in suspension within few minutes was developed. A library of five different plant viruses was obtained combining dielectrophoresis (DEP), performed with a device specifically designed to capture and agglomerate virus particles, and Raman spectroscopy to provide a chemical fingerprint of virions. The tested viruses, purified from infected plants, were chosen for their economic impact on horticultural crops and for their different morphological and structural features. Using the Raman-DEP device, specific profiles for each virus were successfully obtained, relying on chemical differences occurring even with genetically similar viruses belonging to the same taxonomic species and morphologically indiscernible by transmission electron microscopy (TEM). Moreover, we investigated the potentiality of Raman-DEP to follow dynamic changes occurring upon heat treatment of tobacco mosaic virus (TMV) particles. Raman peak deviations linked to TMV coat protein conformation were observed upon treatment at temperatures equal or higher than 85°C, substantiating the rod-to-spherical shape transitions observed by TEM and the concomitant drastic loss of infectivity following plant inoculation. Overall, the Raman-DEP method can be useful for the characterization of virus (nano)particles, setting the basis to create a database suitable for the study of viruses or virus derived-nanoparticles relevant for the agricultural, medical, or biotechnological fields.

Differential Effects of RNA-Dependent RNA Polymerase 6 (RDR6) Silencing on New and Old World Begomoviruses in Nicotiana benthamiana.

RNA-dependent RNA polymerases (RDRs) are key players in the antiviral defence mediated by RNA silencing in plants. RDR6 is one of the major components of the process, regulating the infection of certain RNA viruses. To better clarify its function against DNA viruses, we analyzed the effect of RDR6 inactivation (RDR6i) in N. benthamiana plants on two phloem-limited begomoviruses, the bipartite Abutilon mosaic virus (AbMV) and the monopartite tomato yellow leaf curl Sardinia virus (TYLCSV). We observed exacerbated symptoms and DNA accumulation for the New World virus AbMV in RDR6i plants, varying with the plant growth temperature (ranging from 16 °C to 33 °C). However, for the TYLCSV of Old World origin, RDR6 depletion only affected symptom expression at elevated temperatures and to a minor extent; it did not affect the viral titre. The accumulation of viral siRNA differed between the two begomoviruses, being increased in RDR6i plants infected by AbMV but decreased in those infected by TYLCSV compared to wild-type plants. In situ hybridization revealed a 6.5-fold increase in the number of AbMV-infected nuclei in RDR6i plants but without egress from the phloem tissues. These results support the concept that begomoviruses adopt different strategies to counteract plant defences and that TYLCSV evades the functions exerted by RDR6 in this host.

Overexpression of the C4 protein of tomato yellow leaf curl Sardinia virus increases tomato resistance to powdery mildew.

Powdery mildew (PM) is one of the most important diseases of greenhouse and field-grown tomatoes. Viruses can intervene beneficially on plant performance in coping with biotic and abiotic stresses. Tomato yellow leaf curl Sardinia virus (TYLCSV) has been reported recently to induce tolerance against drought stress in tomato, and its C4 protein acts as the main causal factor of tolerance. However, its role in response to biotic stresses is still unknown. In this study, transgenic tomato plants carrying the TYLCSV C4 protein were exposed to biotic stress following the inoculation with Oidium neolycopersici, the causal agent of tomato PM. Phytopathological, anatomic, molecular, and physiological parameters were evaluated in this plant pathosystem. Heterologous TYLCSV C4 expression increased the tolerance of transgenic tomato plants to PM, not only reducing symptom occurrence, but also counteracting conidia adhesion and secondary hyphae elongation. Pathogenesis-related gene expression and salicylic acid production were found to be higher in tomato transgenic plants able to cope with PM compared to infected wild-type tomato plants. Our study contributes to unraveling the mechanism leading to PM tolerance in TYLCSV C4-expressing tomato plants. In a larger context, the findings of TYLCSV C4 as a novel PM defense inducer could have important implications in deepening the mechanisms regulating the management of this kind of protein to both biotic and abiotic stresses.

Tomato Yellow Leaf Curl Sardinia Virus Increases Drought Tolerance of Tomato.

Drought stress is one of the major physiological stress factors that adversely affect agricultural production, altering critical features of plant growth and metabolism. Plants can be subjected simultaneously to abiotic and biotic stresses, such as drought and viral infections. Rewarding effects provided by viruses on the ability of host plants to endure abiotic stresses have been reported. Recently, begomoviruses causing the tomato yellow leaf curl disease in tomatoes were shown to increase heat and drought tolerance. However, biological bases underlying the induced drought tolerance need further elucidation, particularly in the case of tomato plants. In this work, tomato plants infected by the tomato yellow leaf curl Sardinia virus (TYLCSV) were subjected to severe drought stress, followed by recovery. Morphological traits, water potential, and hormone contents were measured in leaves together with molecular analysis of stress-responsive and hormone metabolism-related genes. Wilting symptoms appeared three days later in TYLCSV-infected plants compared to healthy controls and post-rehydration recovery was faster (2 vs. 4 days, respectively). Our study contributes new insights into the impact of viruses on the plant's adaptability to environmental stresses. On a broader perspective, such information could have important practical implications for managing the effects of climate change on agroecosystems.

The C4 protein of tomato yellow leaf curl Sardinia virus primes drought tolerance in tomato through morphological adjustments.

Viruses can interfere with the ability of plants to overcome abiotic stresses, indicating the existence of common molecular networks that regulate stress responses. A begomovirus causing the tomato yellow leaf curl disease was recently shown to enhance heat tolerance in tomato and drought tolerance in tomato and Nicotiana benthamiana and experimental evidence suggested that the virus-encoded protein C4 is the main trigger of drought responses. However, the physiological and molecular events underlying C4-induced drought tolerance need further elucidation. In this study, transgenic tomato plants expressing the tomato yellow leaf curl Sardinia virus (TYLCSV) C4 protein were subjected to severe drought stress, followed by recovery. Morphometric parameters, water potential, gas exchanges, and hormone contents in leaves were measured, in combination with molecular analysis of candidate genes involved in stress response and hormone metabolism. Collected data proved that the expression of TYLCSV C4 positively affected the ability of transgenic plants to tolerate water stress, by delaying the onset of stress-related features, improving the plant water use efficiency and facilitating a rapid post-rehydration recovery. In addition, we demonstrated that specific anatomical and hydraulic traits, rather than biochemical signals, are the keynote of the C4-associated stress resilience. Our results provide novel insights into the biology underpinning drought tolerance in TYLCSV C4-expressing tomato plants, paving the way for further deepening the mechanism through which such proteins tune the plant-virus interaction.

Raman Spectroscopy Applications in Grapevine: Metabolic Analysis of Plants Infected by Two Different Viruses.

Grapevine is one of the most cultivated fruit plant among economically relevant species in the world. It is vegetatively propagated and can be attacked by more than 80 viruses with possible detrimental effects on crop yield and wine quality. Preventive measures relying on extensive and robust diagnosis are fundamental to guarantee the use of virus-free grapevine plants and to manage its diseases. New phenotyping techniques for non-invasive identification of biochemical changes occurring during virus infection can be used for rapid diagnostic purposes. Here, we have investigated the potential of Raman spectroscopy (RS) to identify the presence of two different viruses, grapevine fan leaf virus (GFLV) and grapevine rupestris stem pitting-associated virus (GRSPaV) in Vitis vinifera cv. Chardonnay. We showed that RS can discriminate healthy plants from those infected by each of the two viruses, even in the absence of visible symptoms, with accuracy up to 100% and 80% for GFLV and GRSPaV, respectively. Chemometric analyses of the Raman spectra followed by chemical measurements showed that RS could probe a decrease in the carotenoid content in infected leaves, more profoundly altered by GFLV infection. Transcriptional analysis of genes involved in the carotenoid pathway confirmed that this biosynthetic process is altered during infection. These results indicate that RS is a cutting-edge alternative for a real-time dynamic monitoring of pathogens in grapevine plants and can be useful for studying the metabolic changes ensuing from plant stresses.

Phylogenetic Marker Selection and Protein Sequence Analysis of the ORF5 Gene Product of Grapevine Virus A.

Grapevine virus A (GVA), the type species of the Vitivirus genus, is one of the causal agents of the Kober stem grooving disease of the rugose wood complex and one of the most frequently detected viruses in grapevine. There is little information on GVA gene(s) marker useful for phylogenetic analysis. To this aim, a total of 403 leaf samples were collected from vineyards of East and West Azarbaijan provinces in the Northwestern provinces of Iran during 2014-2016 and tested by DAS-ELISA and RT-PCR using ORF5-specific primers. GVA was detected in 56 symptomatic samples, corresponding to 14% of infection, while it was not detected in asymptomatic samples. The ORF5 (p10) protein sequence of eight Iranian isolates was compared to other vitiviruses, showing that the most conserved region resides in the N-terminus, carrying an arginine-rich motif followed by a zinc-finger motif. Next, to define a robust phylogenetic marker representative of the whole genome sequence suitable for phylogenetic and evolutionary studies, phylogenetic trees based on the full genome sequences of all the available GVA isolates and on individual genomic regions were constructed and compared. ORF1, which encodes the RNA-dependent RNA polymerase, was found to be the best phylogenetic marker for GVA classification and evolution studies. These results can be used for further research on phylogenetic analyses, evolution history, epidemiology, and etiology of rugose wood complex, and to identify control measures against GVA and other vitiviruses.

Development of a Real-Time Loop-Mediated Isothermal Amplification Assay for the Rapid Detection of Olea Europaea Geminivirus.

A real-time loop-mediated isothermal amplification (LAMP) assay was developed for simple, rapid and efficient detection of the Olea europaea geminivirus (OEGV), a virus recently reported in different olive cultivation areas worldwide. A preliminary screening by end-point PCR for OEGV detection was conducted to ascertain the presence of OEGV in Sicily. A set of six real-time LAMP primers, targeting a 209-nucleotide sequence elapsing the region encoding the coat protein (AV1) gene of OEGV, was designed for specific OEGV detection. The specificity, sensitivity, and accuracy of the diagnostic assay were determined. The LAMP assay showed no cross-reactivity with other geminiviruses and was allowed to detect OEGV with a 10-fold higher sensitivity than conventional end-point PCR. To enhance the potential of the LAMP assay for field diagnosis, a simplified sample preparation procedure was set up and used to monitor OEGV spread in different olive cultivars in Sicily. As a result of this survey, we observed that 30 out of 70 cultivars analyzed were positive to OEGV, demonstrating a relatively high OEGV incidence. The real-time LAMP assay developed in this study is suitable for phytopathological laboratories with limited facilities and resources, as well as for direct OEGV detection in the field, representing a reliable method for rapid screening of olive plant material.

No Evidence for Seed Transmission of Tomato Yellow Leaf Curl Sardinia Virus in Tomato.

Seed transmission is an important factor in the epidemiology of plant pathogens. Geminiviruses are serious pests spread in tropical and subtropical regions. They are transmitted by hemipteran insects, but a few cases of transmission through seeds were recently reported. Here, we investigated the tomato seed transmissibility of the begomovirus tomato yellow leaf curl Sardinia virus (TYLCSV), one of the agents inducing the tomato yellow leaf curl disease, heavily affecting tomato crops in the Mediterranean area. None of the 180 seedlings originating from TYLCSV-infected plants showed any phenotypic alteration typical of virus infection. Moreover, whole viral genomic molecules could not be detected in their cotyledons and true leaves, neither by membrane hybridization nor by rolling-circle amplification followed by PCR, indicating that TYLCSV is not a seed-transmissible pathogen for tomato. Examining the localization of TYLCSV DNA in progenitor plants, we detected the virus genome by PCR in all vegetative and reproductive tissues, but viral genomic and replicative forms were found only in leaves, flowers and fruit flesh, not in seeds and embryos. Closer investigations allowed us to discover for the first time that these embryos were superficially contaminated by TYLCSV DNA but whole genomic molecules were not detectable. Therefore, the inability of TYLCSV genomic molecules to colonize tomato embryos during infection justifies the lack of seed transmissibility observed in this host.

Survey of five major grapevine viruses infecting Blatina and Zilavka cultivars in Bosnia and Herzegovina.

The sanitary status of grapevines has not yet been considered sufficiently in vineyards throughout Bosnia and Herzegovina (BiH). An extensive survey of five major grapevine viruses in the country was carried out in 2019. A total of 630 samples from the two dominant autochthonous cultivars, named Zilavka and Blatina, were tested by DAS-ELISA for the presence of grapevine leafroll-associated viruses (GLRaV-1 and 3), grapevine fleck virus (GFkV), grapevine fanleaf virus (GFLV) and Arabis mosaic virus (ArMV). Eighty-eight % of the samples were positive for at least one virus, and all five viruses were detected, thought with different incidence, i.e. GLRaV-3 (84%), GFLV (43%), GLRaV-1 (14%), GFkV (10%) and ArMV (0.2%). The majority of infected plants (about 75%) were asymptomatic. Specific virus symptoms were observed in the remaining infected plants, together with the reported GLRaV vectors, Planococcus ficus and Parthenolecanium corni, while nematodes of the Xiphinema genus were not found in the GFLV- or ArMV-infected vineyards. The GLRaV-3 CP phylogenetic analyses showed 75-100% nucleotide identity between the BiH and reference isolates, and the BiH isolates clustered into the major group. The dNS/dS ratio indicated a negative selection of the virus population, and the lack of geographical structuring within the population was observed. In addition, putative GLRaV-3 recombinants with breakpoints in the 5' of the CP gene were detected, while no recombinant strains were identified for the other four viruses. The obtained results indicate a deteriorated sanitary status of the cultivated grapevines, the prevalence and intraspecies genetic diversity of GLRaV-3 throughout the country. The establishment of certified grapevine material and adequate virus vector control is therefore of primary importance to prevent further spread of these viruses. This study presents the results of the first molecular characterisation of grapevine viruses in Bosnia and Herzegovina.

The Induction of an Effective dsRNA-Mediated Resistance Against Tomato Spotted Wilt Virus by Exogenous Application of Double-Stranded RNA Largely Depends on the Selection of the Viral RNA Target Region.

Tomato spotted wilt virus (TSWV) is a devastating plant pathogen, causing huge crop losses worldwide. Unfortunately, due to its wide host range and emergence of resistance breaking strains, its management is challenging. Up to now, resistance to TSWV infection based on RNA interference (RNAi) has been achieved only in transgenic plants expressing parts of the viral genome or artificial microRNAs targeting it. Exogenous application of double-stranded RNAs (dsRNAs) for inducing virus resistance in plants, namely RNAi-based vaccination, represents an attractive and promising alternative, already shown to be effective against different positive-sense RNA viruses and viroids. In the present study, the protection efficacy of exogenous application of dsRNAs targeting the nucleocapsid (N) or the movement protein (NSm) coding genes of the negative-sense RNA virus TSWV was evaluated in Nicotiana benthamiana as model plant and in tomato as economically important crop. Most of the plants treated with N-targeting dsRNAs, but not with NSm-targeting dsRNAs, remained asymptomatic until 40 (N. benthamiana) and 63 (tomato) dpi, while the remaining ones showed a significant delay in systemic symptoms appearance. The different efficacy of N- and NSm-targeting dsRNAs in protecting plants is discussed in the light of their processing, mobility and biological role. These results indicate that the RNAi-based vaccination is effective also against negative-sense RNA viruses but emphasize that the choice of the target viral sequence in designing RNAi-based vaccines is crucial for its success.

Plant Molecular Farming as a Strategy Against COVID-19 - The Italian Perspective.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has killed more than 37,000 people in Italy and has caused widespread socioeconomic disruption. Urgent measures are needed to contain and control the virus, particularly diagnostic kits for detection and surveillance, therapeutics to reduce mortality among the severely affected, and vaccines to protect the remaining population. Here we discuss the potential role of plant molecular farming in the rapid and scalable supply of protein antigens as reagents and vaccine candidates, antibodies for virus detection and passive immunotherapy, other therapeutic proteins, and virus-like particles as novel vaccine platforms. We calculate the amount of infrastructure and production capacity needed to deal with predictable subsequent waves of COVID-19 in Italy by pooling expertise in plant molecular farming, epidemiology and the Italian health system. We calculate the investment required in molecular farming infrastructure that would enable us to capitalize on this technology, and provide a roadmap for the development of diagnostic reagents and biopharmaceuticals using molecular farming in plants to complement production methods based on the cultivation of microbes and mammalian cells.

Nondestructive Raman Spectroscopy as a Tool for Early Detection and Discrimination of the Infection of Tomato Plants by Two Economically Important Viruses.

Global population forecasts dictate a rapid adoption of multifaceted approaches to fulfill increasing food requirements, ameliorate food dietary value and security using sustainable and economically feasible agricultural processes. Plant pathogens induce up to 25% losses in vegetable crops and their early detection would contribute to limit their spread and economic impact. As an alternative to time-consuming, destructive, and expensive diagnostic procedures, such as immunological assays and nucleic acid-based techniques, Raman spectroscopy (RS) is a nondestructive rapid technique that generates a chemical fingerprinting of a sample, at low operating costs. Here, we assessed the suitability of RS combined to chemometric analysis to monitor the infection of an important vegetable crop plant, tomato, by two dangerous and peculiarly different viral pathogens, Tomato yellow leaf curl Sardinia virus (TYLCSV) and Tomato spotted wilt virus (TSWV). Experimentally inoculated plants were monitored over 28 days for symptom occurrence and subjected to RS analysis, alongside with measuring the virus amount by quantitative real-time PCR. RS allowed to discriminate mock inoculated (healthy) from virus-infected specimens, reaching an accuracy of >70% after only 14 days after inoculation for TYLCSV and >85% only after 8 days for TSWV, demonstrating its suitability for early detection of virus infection. Importantly, RS also highlighted spectral differences induced by the two viruses, providing specific information on the infecting agent.

Engineering partial resistance to cucumber mosaic virus in tobacco using intrabodies specific for the viral polymerase.

A single-chain variable antibody fragment (scFv) library tested against the non-structural NSP5 protein of human rotavirus A was screened by a yeast two-hybrid system against three proteins derived from the RNA-dependent RNA polymerase (RdRp) of cucumber mosaic virus (CMV), with the aim of blocking their function and preventing viral infection once expressed in planta. The constructs tested were (i) '2a' consisting of the full-length 2a gene (839 amino acids, aa), (ii) 'Motifs' covering the conserved RdRp motifs (IV-VII) (132 aa) and (iii) 'GDD' located within the conserved RdRp motif VI (GDD, 22 aa). In yeast two-hybrid (Y2H) selection assays the '2a' and 'Motifs' constructs interacted with 96 and 25 library constructs, respectively, while the 'GDD' construct caused transactivation. Y2H-interacting scFvs were analyzed in vivo for their interaction with the 2a and Motifs proteins in a mammalian transient expression system. Eighteen tobacco lines stably transformed with four selected scFvs were produced and screened for resistance against two different CMV isolates. Different levels of resistance and rate of recovery were observed with CMV of both groups I and II, particularly in lines expressing intrabodies against the full-length 2a protein. This work describes for the first time the use of intrabodies against the RdRp of CMV to obtain plants that reduce infection of a pandemic virus, showing that the selected scFvs can modulate virus infection and induce premature recovery in tobacco plants.

Virus-mediated export of chromosomal DNA in plants.

The propensity of viruses to acquire genetic material from relatives and possibly from infected hosts makes them excellent candidates as vectors for horizontal gene transfer. However, virus-mediated acquisition of host genetic material, as deduced from historical events, appears to be rare. Here, we report spontaneous and surprisingly efficient generation of hybrid virus/host DNA molecules in the form of minicircles during infection of Beta vulgaris by Beet curly top Iran virus (BCTIV), a single-stranded DNA virus. The hybrid minicircles replicate, become encapsidated into viral particles, and spread systemically throughout infected plants in parallel with the viral infection. Importantly, when co-infected with BCTIV, B. vulgaris DNA captured in minicircles replicates and is transcribed in other plant species that are sensitive to BCTIV infection. Thus, we have likely documented in real time the initial steps of a possible path of virus-mediated horizontal transfer of chromosomal DNA between plant species.

Self-Assembling Plant-Derived Vaccines Against Papillomaviruses.

Virus-like particles (VLPs) can be used as antiviral vaccines as they mimic the structure of virus particles, with preserved conformation and immunogenicity characteristics. L1, the major capsid protein of papillomaviruses (PV) can self-assemble into VLPs currently used as highly effective vaccines. VLPs can be produced in heterologous systems, including plants. Here, a method for the expression of the L1 protein of human papillomavirus 16 (HPV 16) and the production of highly purified preparations of HPV 16 L1 VLPs is described. The method relies on the transient expression of HPV 16 L1 in Nicotiana benthamiana plants using a nonreplicating vector and on the purification of VLPs by different centrifugation steps followed by a cesium sulfate gradient. Such a procedure has also been successfully applied to other HPVs and to bovine papillomavirus 1.

Deep Sequencing Data and Infectivity Assays Indicate that Chickpea Chlorotic Dwarf Virus is the Etiological Agent of the "Hard Fruit Syndrome" of Watermelon.

Chickpea chlorotic dwarf virus (CpCDV), a polyphagous mastrevirus, family Geminiviridae, has been recently linked to the onset of the "hard fruit syndrome" of watermelon, first described in Tunisia, that makes fruits unmarketable due to the presence of white hard portions in the flesh, chlorotic mottling on the rind, and an unpleasant taste. To investigate the etiological agent of this disease, total RNA extracted from symptomatic watermelon fruits was subjected to small RNA sequencing through next generation sequencing (NGS) techniques. Data obtained showed the presence of CpCDV and two other viral species. However, following validation through polymerase chain reaction (PCR), CpCDV was the only viral species consistently detected in all samples. Watermelon seedlings were then challenged by an agroinfectious CpCDV clone; several plants proved to be CpCDV-infected, and were able to produce fruits. CpCDV infected and replicated in watermelon fruits and leaves, leading to abnormality in fruits and in seed production, similar to those described in field. These results indicate that CpCDV is the etiological agent of the "hard fruit syndrome" of watermelon.

Cloning and Expression Analysis of Human Amelogenin in Nicotiana benthamiana Plants by Means of a Transient Expression System.

Enamel is the covering tissue of teeth, made of regularly arranged hydroxyapatite crystals deposited on an organic matrix composed of 90% amelogenin that is completely degraded at the end of the enamel formation process. Amelogenin has a biomineralizing activity, forming nanoparticles or nanoribbons that guide hydroxyapatite deposit, and regenerative functions in bone and vascular tissue and in wound healing. Biotechnological products containing amelogenin seem to facilitate these processes. Here, we describe the production of human amelogenin in plants by transient transformation of Nicotiana benthamiana with constructs carrying synthetic genes with optimized human or plant codons. Both genes yielded approximately 500 µg of total amelogenin per gram of fresh leaf tissue. Two purification procedures based on affinity chromatography or on intrinsic solubility properties of the protein were followed, yielding from 12 to 150 µg of amelogenin per gram of fresh leaf tissue, respectively, at different purity. The identity of the plant-made human amelogenin was confirmed by MALDI-TOF-MS analysis of peptides generated following chymotrypsin digestion. Using dynamic light scattering, we showed that plant extracts made in acetic acid containing human amelogenin have a bimodal distribution of agglomerates, with hydrodynamic diameters of 22.8 ± 3.8 and 389.5 ± 86.6 nm. To the best of our knowledge, this is the first report of expression of human amelogenin in plants, offering the possibility to use this plant-made protein for nanotechnological applications.