Allergenicity assessment of the papaya ringspot virus coat protein expressed in transgenic rainbow papaya

DsRNA-mediated protection against two isolates of Papaya ringspot virus through topical application of dsRNA in papaya

Papaya ringspot virus (PRSV) infections in papaya result in heavy yield losses, severely affecting the papaya industry worldwide, and hence warranting for effective control measures. In the past, transgenic papaya cultivars were developed that overexpressed parts of the PRSV genome and exhibited high levels of virus resistance. In the present study, a non-transgenic approach was employed, in which in vitro produced dsRNA molecules derived from a PRSV isolate from South India (PRSV-Tirupati) was tested for dsRNA-mediated protection against two isolates of PRSV through topical application of the dsRNA on papaya. The results showed that the dsRNA molecules from both the coat protein (CP) and helper component-proteinase (HC-Pro) genes of the PRSV-Tirupati isolate conferred 100 % resistance against PRSV-Tirupati infection. Further, the same dsRNA molecules were highly effective against the PRSV-Delhi isolate on the papaya cv. Pusa Nanha, conferring a resistance of 94 % and 81 %, respectively. Systemic papaya leaves of the dsRNA-treated plants were virus-free at 14 days post-inoculation, confirming the robustness of this non-transgenic virus control strategy. In contrast, the control TMV dsRNA did not protect against the PRSV infection. This study on the topical application of dsRNA opened up a new avenue for the control of papaya ringspot disease worldwide.

Spectrum of Allergens and Allergen Biology in India

The growing prevalence of allergy and asthma in India has become a major health concern with symptoms ranging from mild rhinitis to severe asthma and even life-threatening anaphylaxis. The "allergen repertoire" of this subcontinent is highly diverse due to the varied climate, flora, and food habits. The proper identification, purification, and molecular characterization of allergy-eliciting molecules are essential in order to facilitate an accurate diagnosis and to design immunotherapeutic vaccines. Although several reports on prevalent allergens are available, most of these studies were based on preliminary detection and identification of the allergens. Only a few of these allergen molecules have been characterized by recombinant technology and structural biology. The present review first describes the composition, distribution pattern, and natural sources of the predominant allergens in India along with the prevalence of sensitization to these allergens across the country. We go on to present a comprehensive report on the biochemical, immunological, and molecular information on the allergens reported so far from India. The review also covers the studies on allergy- related biosafety assessment of transgenic plants. Finally, we discuss the allergen-specific immunotherapy trials performed in India.

Subchronic Immunotoxicity Assessment of Genetically Modified Virus-Resistant Papaya in Rats

Papaya is an important fruit that provides a variety of vitamins with nutritional value and also holds some pharmacological properties, including immunomodulation. Genetically modified (GM) papaya plants resistant to Papaya ringspot virus (PRSV) infection have been generated by cloning the coat protein gene of the PRSV which can be used as a valuable strategy to fight PRSV infection and to increase papaya production. In order to assess the safety of GM papaya as a food, this subchronic study was conducted to assess the immunomodulatory responses of the GM papaya line 823-2210, when compared with its parent plant of non-GM papaya, Tainung-2 (TN-2), in Sprague-Dawley (SD) rats. Both non-GM and GM 823-2210 papaya fruits at low (1 g/kg bw) and high (2 g/kg bw) dosages were administered via daily oral gavage to male and female rats consecutively for 90 days. Immunophenotyping, mitogen-induced splenic cell proliferation, antigen-specific antibody response, and histopathology of the spleen and thymus were evaluated at the end of the experiment. Results of immunotoxicity assays revealed no consistent difference between rats fed for 90 days with GM 823-2210 papaya fruits, as opposed to those fed non-GM TN-2 papaya fruits, suggesting that with regard to immunomodulatory responses, GM 823-2210 papaya fruits maintain substantial equivalence to fruits of their non-GM TN-2 parent.

Using LC-MS Based Methods for Testing the Digestibility of a Nonpurified Transgenic Membrane Protein in Simulated Gastric Fluid

The digestibility of a nonpurified transgenic membrane protein was determined in pepsin, as part of the food safety evaluation of its resistance to digestion and allergenic potential. Delta-6-desaturase from Saprolegnia diclina, a transmembrane protein expressed in safflower for the production of gamma linolenic acid in the seed, could not be obtained in a pure, native form as normally required for this assay. As a novel approach, the endoplasmic reticulum isolated from immature seeds was digested in simulated gastric fluid (SGF) and the degradation of delta-6-desaturase was selectively followed by SDS-PAGE and targeted LC-MS/MS quantification using stable isotope-labeled peptides as internal standards. The digestion of delta-6-desaturase by SGF was shown to be both rapid and complete. Less than 10% of the initial amount of D6D remained intact after 30 s, and no fragments large enough (>3 kDa) to elicit a type I allergenic response remained after 60 min.

Transcriptome Profiling Revealed Stress-Induced and Disease Resistance Genes Up-Regulated in PRSV Resistant Transgenic Papaya

Papaya is a productive and nutritious tropical fruit. Papaya Ringspot Virus (PRSV) is the most devastating pathogen threatening papaya production worldwide. Development of transgenic resistant varieties is the most effective strategy to control this disease. However, little is known about the genome-wide functional changes induced by particle bombardment transformation. We conducted transcriptome sequencing of PRSV resistant transgenic papaya SunUp and its PRSV susceptible progenitor Sunset to compare the transcriptional changes in young healthy leaves prior to infection with PRSV. In total, 20,700 transcripts were identified, and 842 differentially expressed genes (DEGs) randomly distributed among papaya chromosomes. Gene ontology (GO) category analysis revealed that microtubule-related categories were highly enriched among these DEGs. Numerous DEGs related to various transcription factors, transporters and hormone biosynthesis showed clear differences between the two cultivars, and most were up-regulated in transgenic papaya. Many known and novel stress-induced and disease-resistance genes were most highly expressed in SunUp, including MYB, WRKY, ERF, NAC, nitrate and zinc transporters, and genes involved in the abscisic acid, salicylic acid, and ethylene signaling pathways. We also identified 67,686 alternative splicing (AS) events in Sunset and 68,455 AS events in SunUp, mapping to 10,994 and 10,995 papaya annotated genes, respectively. GO enrichment for the genes displaying AS events exclusively in Sunset was significantly different from those in SunUp. Transcriptomes in Sunset and transgenic SunUp are very similar with noteworthy differences, which increased PRSV-resistance in transgenic papaya. No detrimental pathways and allergenic or toxic proteins were induced on a genome-wide scale in transgenic SunUp. Our results provide a foundation for unraveling the mechanism of PRSV resistance in transgenic papaya.

Repeated Dose 90-Day Feeding Study of Whole Fruits of Genetically Modified Papaya Resistant to Papaya Ringspot Virus in Rats

Genetically modified (GM) papaya plants resistant to infection by Papaya ringspot virus (PRSV) have been successfully generated by cloning the coat protein (CP) gene of PRSV to increase fruit production. In this study, the GM papaya line 823-2210 was used to conduct a 90-day feeding toxicity study and compared to its parent plant of non-GM papaya, Tainung-2 (TN-2) based on the experimental guidance reported by the European Food Safety Authority.1 Ten male and 10 female Sprague-Dawley albino rats were gavaged at low (1 g/kg bw) and high (2 g/kg bw) doses of non-GM and GM lyophilized papaya fruits for 90 days. Hematology, coagulation, biochemistry, urinalysis, and pathology were examined in all animals. Although some differences were found in feed consumption, hematology, and serum chemistry examinations between non-GM and GM papaya, the results were within historical control values and not considered biologically significant in rats. In addition, there were no treatment-related gross or microscopic lesions in male or female rats attributable to the non-GM or GM papaya fruit. This 90-day feeding study of GM papaya fruit did not reveal adverse effects in rats and indicates that GM papaya fruits may be substantially equivalent to their non-GM parent plants.

The wayward Hawaiian boy returns home

This chapter represents a travelog of my life and career and the philosophical points I acquired along the way. I was born on a sugar plantation on the island of Hawaii and early on had a stuttering problem. I attended the Kamehameha Schools and received my BS and MS degrees from the University of Hawaii and my Ph.D. from the University of California at Davis. I link my life and career to various principles and events, some of which are: the importance of positioning oneself; going for the big enchilada; music, the international language; the red zone of biotechnology; the human side of biotechnology; the transgenic papaya story; and my leadership time at USDA in Hawaii. The guiding light throughout my career were the words from Drs. Eduardo Trujillo and Robert Shepherd, respectively, "Dennis, don't just be a test tube scientist, do something to help people" and "Now tell me, what have you really accomplished?"

Gene technology for papaya ringspot virus disease management

Papaya (Carica papaya) is severely damaged by the papaya ringspot virus (PRSV). This review focuses on the development of PRSV resistant transgenic papaya through gene technology. The genetic diversity of PRSV depends upon geographical distribution and the influence of PRSV disease management on a sequence of PRSV isolates. The concept of pathogen-derived resistance has been employed for the development of transgenic papaya, using a coat protein-mediated, RNA-silencing mechanism and replicase gene-mediated transformation for effective PRSV disease management. The development of PRSV-resistant papaya via post-transcriptional gene silencing is a promising technology for PRSV disease management. PRSV-resistant transgenic papaya is environmentally safe and has no harmful effects on human health. Recent studies have revealed that the success of adoption of transgenic papaya depends upon the application, it being a commercially viable product, bio-safety regulatory issues, trade regulations, and the wider social acceptance of the technology. This review discusses the genome and the genetic diversity of PRSV, host range determinants, molecular diagnosis, disease management strategies, the development of transgenic papaya, environmental issues, issues in the adoption of transgenic papaya, and future directions for research.

Complete genome of Hainan papaya ringspot virus using small RNA deep sequencing

Small RNA deep sequencing allows for virus identification, virus genome assembly, and strain differentiation. In this study, papaya plants with virus-like symptoms collected in Hainan province were used for deep sequencing and small RNA library construction. After in silicon subtraction of the papaya sRNAs, small RNA reads were used to in the viral genome assembly using a reference-guided, iterative assembly approach. A nearly complete genome was assembled for a Hainan isolate of papaya ringspot virus (PRSV-HN-2). The complete PRSV-HN-2 genome (accession no.: KF734962) was obtained after a 15-nucleotide gap was filled by direct sequencing of the amplified genomic region. Direct sequencing of several random genomic regions of the PRSV isolate did not find any sequence discrepancy with the sRNA-assembled genome. The newly sequenced PRSV-HN-2 genome shared a nucleotide identity of 96 and 94 % to that of the PRSV-HN (EF183499) and PRSV-HN-1 (HQ424465) isolates, and together with these two isolates formed a new PRSV clade. These data demonstrate that the small RNA deep sequencing technology provides a viable and rapid mean to assemble complete viral genomes in plants.

Progress towards the 'Golden Age' of biotechnology

Biotechnology uses substances, materials or extracts derived from living cells, employing 22 million Europeans in a € 1.5 Tn endeavour, being the premier global economic growth opportunity this century. Significant advances have been made in red biotechnology using pharmaceutically and medically relevant applications, green biotechnology developing agricultural and environmental tools and white biotechnology serving industrial scale uses, frequently as process feedstocks. Red biotechnology has delivered dramatic improvements in controlling human disease, from antibiotics to overcome bacterial infections to anti-HIV/AIDS pharmaceuticals such as azidothymidine (AZT), anti-malarial compounds and novel vaccines saving millions of lives. Green biotechnology has dramatically increased food production through Agrobacterium and biolistic genetic modifications for the development of 'Golden Rice', pathogen resistant crops expressing crystal toxin genes, drought resistance and cold tolerance to extend growth range. The burgeoning area of white biotechnology has delivered bio-plastics, low temperature enzyme detergents and a host of feedstock materials for industrial processes such as modified starches, without which our everyday lives would be much more complex. Biotechnological applications can bridge these categories, by modifying energy crops properties, or analysing circulating nucleic acid elements, bringing benefits for all, through increased food production, supporting climate change adaptation and the low carbon economy, or novel diagnostics impacting on personalized medicine and genetic disease. Cross-cutting technologies such as PCR, novel sequencing tools, bioinformatics, transcriptomics and epigenetics are in the vanguard of biotechnological progress leading to an ever-increasing breadth of applications. Biotechnology will deliver solutions to unimagined problems, providing food security, health and well-being to mankind for centuries to come.

Toxicity assessment of transgenic papaya ringspot virus of 823-2210 line papaya fruits

The transgenic papaya is a valuable strategy for creating plants resistant to papaya ringspot virus (PRSV) infection and increasing production. This study was further performed to evaluate the comparative toxicity effects of the newly developed transgenic line of the fruits of two backcross transgenic papaya lines (2210 and 823) and one hybrid line (823-2210) and compare to their parent non-transgenic (TN-2) counterparts. The stability analysis of coat protein (CP) of PRSV was investigated using the digestion stability assays in simulated gastric fluid (SGF), simulated intestinal fluid (SIF), and bile salts to detect the CP fragments. Results revealed that the CP fragments were rapidly hydrolyzed in SGF and were undetectable in organs and gastrointestinal contents in rats. For the genotoxicity, three in vitro assays were conducted and exhibited that non-transgenic and backcross transgenic papaya fruits were negative. Moreover, a repeated animal feeding study was conducted by feeding 2 g/kg of body weight (bw) of non-transgenic and backcross transgenic papaya fruits for 28 days in rats. There were no biological or toxicological significances between non-transgenic and backcross transgenic papaya fruits in rats. The results demonstrated that the backcross transgenic papaya fruit can be recognized as an equivalent substitution for traditional papaya in food safety.

Application of a qualitative and quantitative real-time polymerase chain reaction method for detecting genetically modified papaya line 55-1 in papaya products

Genetically modified (GM) papaya (Carica papaya L.) line 55-1 (55-1), which is resistant to papaya ringspot virus infection, has been marketed internationally. Many countries have mandatory labeling regulations for GM foods, and there is a need for specific methods for detecting 55-1. Here, an event- and construct-specific real-time polymerase chain reaction (PCR) method was developed for detecting 55-1 in papaya products. Quantitative detection was possible for fresh papaya fruit up to dilutions of 0.001% and 0.01% (weight per weight [w/w]) for homozygous SunUp and heterozygous Rainbow cultivars, respectively, in non-GM papaya. The limit of detection and quantification was as low as 250 copies of the haploid genome according to a standard reference plasmid. The method was applicable to qualitative detection of 55-1 in eight types of processed products (canned papaya, pickled papaya, dried fruit, papaya-leaf tea, jam, puree, juice, and frozen dessert) containing papaya as a main ingredient.