Twenty years ago Hawaiian papaya farmers were in trouble. Fig. A. Garcia, “RNA helicase: a novel activity associated with a protein encoded by a positive strand RNA virus,”, P. F. Tennant, C. Gonsalves, K. S. Ling et al., “Differential protection against papaya ringspot virus isolates in coat protein gene transgenic papaya and classically cross-protected Papaya,”, M. F. Bateson, J. Henderson, W. Chaleeprom, A. J. Gibbs, and J. L. Dale, “Papaya ringspot potyvirus: isolate variability and the origin of PRSV type P (Australia),”, H. Quemada, B. L'Hostis, D. Gonsalves et al., “The nucleotide sequences of the 3'-terminal regions of papaya ringspot virus strains W and P,”, R. K. Jain, J. Sharma, A. S. Sivakumar et al., “Variability in the coat protein gene of Papaya ringspot virus isolates from multiple locations in India,”, L. Silva-Rosales, N. Becerra-Leor, S. Ruiz-Castro, D. Téliz-Ortiz, and J. C. Noa-Carrazana, “Coat protein sequence comparisons of three Mexican isolates of papaya ringspot virus with other geographical isolates reveal a close relationship to American and Australian isolates,”, M. F. Bateson, R. E. Lines, P. Revill et al., “On the evolution and molecular epidemiology of the potyvirus Papaya ringspot virus,”, X. The most important step is identification of virus for effective PRSV control. This resistance was still evident up to termination of the trials in early 1998. Picture taken in 1999. The VPg is required for priming RNA synthesis. 1. PRSV inoculum source existed in a nearby infected block of nontransgenic Sunrise as well as selected Sunrise plants in the border rows that were mechanically inoculated with PRSV. Transgenic Virus Resistant Papaya: From Hope to Reality for Controlling Papaya Ringspot Virus in Hawaii, The American Phytopathological Society (APS), Gonsalves, D., Gonsalves, C., Ferreira, S., Pitz, K., Fitch, M, Manshardt, R. and Slightom, J. So far, we have not observed breakdown of resistance of Rainbow in Puna or on Oahu. Yeh and Gonsalves [90] reported that there were no ill effects after the consumption of PRSV-resistant transgenic papaya. Transgenic flow is a major concern amongst growers, exporters, and consumers. PRSV might have been transported from India to America in the early 18th century and spread in 19th and 20th centuries [40]. The geographical origin of papaya is Southern Mexico and Costa Rica [1]. This is a voluntary program. This approach also has the advantage that it allows the grower to produce transgenic and nontransgenic papaya in relatively close proximity. Yen, “Efficient transformation of papaya by coat protein gene of papaya ringspot virus mediated by, R. E. Lines, D. Persley, J. L. Dale, R. Drew, and M. F. Bateson, “Genetically engineered immunity to Papaya ringspot virus in Australian papaya cultivars,”, P. Tennant, M. H. Ahmad, and D. Gonsalves, “Transformation of, M. A. K. Azad, M. G. Rabbani, L. Amin, and N. M. Sidik, “Development of transgenic papaya through, M. J. Davis and Z. Ying, “Genetic diversity of the Papaya ringspot virus in Florida,”, M. M. M. Fitch, “Carica papaya Papaya,” in, C. Gonsalves, W. Cai, P. F. Tennant, and D. Gonsalves, “Effective development of papaya ringspot virus resistant papaya with untranslatable coat protein gene using a modified microprojectile transformation method,”, H. J. Bau, Y. H. Cheng, T. A. Yu et al., “Field evaluation of transgenic papaya lines carrying the coat protein gene of Papaya ringspot virus in Taiwan,”, P. M. Magdalita, L. D. Valencia, A. T. I. D. Ocampo et al., “Towards development of PRSV resistant papaya by genetic engineering. The development of transgenic papaya to prevent infection by PRSV has been employed after the successful development of transgenic tobacco, expressing the CP gene of the tobacco mosaic virus, which showed disease resistance. The GMO papaya, called the Rainbow papaya, is an example of a GMO crop developed to be resistant to a virus. PRSV isolates and the sequence for PRSV CP genes have been presented in Table 1. 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. First, the initial large-scale planting of transgenic papaya in established farms along with the elimination of abandoned virus-infected fields drastically reduced the amount of available virus inoculum. The CP gene can carry determinants for pathogenicity and the properties of the virus in transgenic plants might be changed. Jyoti Sharma; Jain RK; Ramiah M; Varma A, 2005. Resistance of Rainbow held up even under strong inoculum pressure of PRSV. Ann. 1. Fig. SunUp and Rainbow cultivars were developed from the initial field trial and showed excellent resistance and horticultural qualities in the large scale field trial in Puna. The “green” or unripe fruits can be used as vegetables. If approved by HDOA, fruit from these fields can be harvested. However, it is very likely that the process will take much more time than it did in Hawaii. Symptoms of PRSV manifest as a prominent mosaic pattern on the leaf lamina, wet-oily streaks on the petioles and upper part of the trunk, and the distortion of young leaves. Drew, “Greenhouse and field evaluations of coat-protein transgenic papaya resistant to papaya ringspot virus,”, M. Sreenivasulu and D. V. R. SaiGopal, “Development of recombinant coat protein antibody based IC-RT-PCR and comparison of its sensitivity with other immunoassays for the detection of papaya ringspot virus isolates from India,”, S. Ruiz-Castro and L. Silva-Rosales, “Use of RT-PCR for papaya ringspot virus detection in papaya (, F. D. Smith and E. E. Bantari, “Dot ELISA on nitrocellulose membrane for detection of potato leaf roll virus,”. It is an excellent source of beta carotene which may prevent cancer, diabetes, and heart disease [4]. The genetic diversity of PRSV was observed in different regions of the world [34]. Major challenges face the adoption of transgenic papaya which include the application of the biotechnological protocols for the development of transgenic papaya, its viability as a commercial product, biosafety regulatory issues, and trade regulations. 2003. Production of papaya in Puna increased starting in 2000 and peaked at 40 million pounds in 2001 with 35 million pounds being produced in 2002. Some of these are penetrating the markets in Canada and Japan, growing nontransgenic papaya, and the durability of the resistance of transgenic papaya. Transgenic Virus-Resistant Papaya: From Hope to Reality in Controlling Papaya Ringspot Virus in Hawaii. In addition, initial hybrids that were made with Rainbow and nontransgenic Kamiya have been backcrossed four times to nontransgenic Kamiya. 6). Papaya Ringspot Virus (Potyvirus PRSV) infected leaves Papaya ringspot symptoms on fruit. An APSnet Feature published in 1998 described the ensuing damage caused by PRSV in Puna and the timely efforts to develop, evaluate, and deregulate the transgenic papaya (5). Therefore, country-specific varieties of PRSV-resistant transgenic papaya should be developed through PTGS technology using geographically distinct PRSV isolates. The effect of PRSV on papaya production in Puna can also be seen by the drop in the total percentage of Hawaii’s fresh papaya production that was produced in Puna. [91] observed that transgene derived PRSV CP did not pose any risk of food allergies. There remain challenges to the Hawaii papaya industry, mainly in getting the transgenic papaya approved for sale in Japan. Using the concept of pathogen-derived resistance, the coat protein gene of a mild mutant of a PRSV strain from Hawaii was used in biolistic transformation of embryogenic cultures of red-fleshed Sunset cultivar (2). [34] reported that R1 transgenic papaya of line 55-1 showed narrow resistance after inoculation in greenhouse. Funding to produce the seeds was obtained by PAC. Variation in the CP gene sequences of PRSV was observed in different parts of the world [35]. University of Hawaii College of Tropical Agriculture and Human Resources New Plants for Hawaii-1:2pp. Ruiz-Castro and Silva-Rosales [47] reported that reverse transcription and polymerase chain reaction (RT-PCR) showed reliable results for the detection of PRSV in papaya samples. This problem can be overcome by the silencing suppressor protein HcPro, through an RNA-silencing mechanism within transgenic papaya. Fortunately, our research had resulted in the development of a transgenic papaya that was resistant to PRSV; in fact, an initial field trial of the transgenic papaya was established on Oahu island at about the time PRSV was discovered in Puna (2,6). Meanwhile, it is critical that papaya shipments to Japan are not contaminated with transgenic papaya. 2001. There have been some studies upon the development of PRSV-resistant varieties of C. papaya through gene technology but no review article on PRSV disease management is available. Dot immune binding assay (DIBA) is useful for virus indexing, as it is a simple and cheap method for large scale virus detection [48]. Plant Health Progress doi:10.1094/PHP-2003-1113-03-RV. This research group has applied the concept of pathogen derived resistance which has stimulated research into obtaining virus resistance through gene technology. 107:645-653. Cheng et al. Front cover of a brochure distributed during the celebration on the inaugural seed distribution of transgenic Rainbow and SunUp to growers on May 1, 1998. The PRSV-W type affects cucurbits but not papaya while the PRSV-P type affects papaya and cucurbits. 10:1466-1472. 5. Common Name. Thus, Rainbow plantings are constantly being monitored for evidence of breakdown of resistance. Gonsalves, D., Ferreira, S., Manshardt, R., Fitch, M., and Slightom, J. So, vector nontransmissible virus in transgenic plants would be transformed into a transmissible virus through heteroencapsidation resulting in new viral epidemics. The breakdown of PRSV resistance is the main problem associated with PRSV-resistant papaya. Chen et al. Human assisted movement of infected papaya (pawpaw or papaw) plants and cucurbit seedlings could easily spread the virus and is the most likely way this disease could spread over long distances. The virus is transmitted by several species of aphids in a nonpersistent manner. The results were dramatic, all nontransgenic plants became infected within 11 months of starting the field trail while none of the transgenic test plants became infected (Fig. Transgenic papaya developed by various research groups through gene technology. It can affect the microRNA-mediated development pathway in plants and help in the establishment of the heterologous virus. Comparative infection of transgenic and nontransgenic papaya in the 1995 field trial in Kapoho (see Fig. [68] developed genetically engineered papaya using the CP gene of Philippine PRSV and regenerated putative transgenic R0 plantlets, which were moderately susceptible whilst R1 plantlets were completely resistant. Bau, Y.-H. Cheng, T.-A. Tennant, P., G. Fermin, M. M. Fitch, R. M. Manshardt, J. L. Slightom, and D. Gonsalves. Papaya is a dicotyledonous, polygamous, and diploid species. [66] used gene gun technology when transferring an untranslatable CP gene for the development of a PRSV-resistant papaya variety. Transgenic plants have potential allergenic properties due to the protein encoded by viral sequences [23]. Papaya crops are currently beset by disease problems especially those caused by the papaya ringspot virus (PRSV) [6, 7]. Unlike the other cases, the objective is to improve human health by making papaya readily available to the rural farmers or villagers who are often poor and show acute vitamin deficiency (especially vitamin A). HC-Pro is responsible for synergism between polyviruses and unrelated viruses that can cause severe symptoms and an accumulation of virus in infected leaves [31]. Wang, “Virus resistance and gene silencing in plants can be induced by simultaneous expression of sense and antisense RNA,”, A. Eamens, M.-B. This review focuses on the development of PRSV resistant transgenic papaya through gene technology. APS. The diversity at amino acid and nucleic acid levels was highest among the Asian population of PRSV isolates [37]. The latter will reduce the amount of available PRSV inoculum.
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