Ringspot virus resistant papaya

Plant Disease: Davis, M. State Hort. Resistance to Papaya ringspot virus in transgenic papaya breeding lines. Sponsoring Institution. Project Director Davis, M. Non Technical Summary Papaya ringspot virus is the major limiting factor in papaya production in Florida and some other areas of the Caribbean region This project will develop papaya varieties for the region that have foreign genes conferring resistance to ringspot virus.

Animal Health Component. Research Effort Categories Basic. We now seek to enhance commercial papaya production in the Caribbean region by developing papaya varieties with transgenic resistance to PRV. Prior to initiation of this proposed project, we will have selected several lines of transgenic PRV-resistant papaya for continued development. The lines will have been derived from initial crosses of transgenic female parents with elite papaya genotypes followed by self-fertilization and selection for three generations.

Limited attempts have been made in the world to evolve superior varieties of papaya. Our long-term goal is to develop true-breeding papaya varieties from our transgenic lines. With PRV controlled, our main breeding objective is aimed at producing high yielding gynodioecious varieties with good quality fruit. The specific objectives of this project will be to: 1. Develop transgenic, PRV-resistant papaya varieties by selection within inbred lines to stabilize desired phenotypes; 2.

Evaluate performance of advanced breeding selections compared to non-transgenic counterparts; 3. Evaluate effects of hemizygous versus homozygous transgenes and the combination of different transgenic constructs for additive resistance to PRV. Project Methods Transgenic, PRV-resistant, papaya varieties will be developed by selection within inbred lines to stabilize desired phenotypes.

Breeding lines will be established that are homozygous for the transgenes. R3 seedlings will have been screened for homozygousity of transgenes by examining segregation of kanamycin resistance. The adoption of PRSV-resistant transgenic papaya is still slow and it depends upon the demand for papaya, biosafety regulations, and social acceptance of the technology. Recent studies indicate that PRSV-resistant transgenic papaya is environmentally safe and has no adverse effects on human health.

This review suggests that papaya producing countries should develop PRSV-resistant transgenic papaya using their own PRSV isolates through posttranscriptional gene silencing technology. National Center for Biotechnology Information , U. Journal List ScientificWorldJournal v. Published online Mar Abul Kalam Azad. Author information Article notes Copyright and License information Disclaimer.

Abul Kalam Azad: moc. Received Dec 19; Accepted Feb 1. Abul Kalam Azad et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This article has been cited by other articles in PMC. Introduction Papaya Carica papaya L belongs to the family Caricaceaeand is one of the most economically important fruit crops in many tropical and subtropical countries.

Open in a separate window. Figure 1. Name Biotype Origin Gene Bank accession no. Host Range Determinants and Vector Transmission Plant viruses spread from cell to cell with the interaction of virus and host factors. Gene Technology for the Development of PRSV-Resistant Transgenic Papaya Generally crops with resistance to viral disease may be developed through genes derived from viral sequences providing pathogen derived resistance PDR , genes from various other sources that can interfere with target virus, and natural resistance genes.

Coat Protein CP Mediated Resistance 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.

Table 2 Transgenic papaya developed by various research groups through gene technology. Replicase Gene-Mediated Resistance The resistance mechanism is protein-based because the resistance phenotype is influenced by mutations affecting the primary structure of the protein encoded by the transgene. Factors to Be Considered for the Adoption of Transgenic Papaya Despite the potential and benefits of transgenic papaya, the adoption rate of transgenic papaya is extremely low.

Environment Issues and Food Safety Transgenic crops are subject biosafety rules due to possibly negative impacts of the plants on the environment, human, and animal health. Current Challenges and Future Prospects Transgenic papaya is the most advanced technology extant for plant disease management [ 95 ].

Conclusion PRSV is the major threat for papaya production. Conflict of Interests The authors declare that there is no conflict of interests. References 1. DeCandolle A. Origin of Cultivated Plants. Breaking the intergeneric hybridization barrier in Carica papaya and Vasconcellea cauliflora.

Scientia Horticulturae. Plant regeneration and somatic embryogenesis from immature embryos derived through interspecific hybridization among different Carica species. International Journal of Molecular Science. Traditional and medicinal uses of Carica papaya. Journal of Medicinal Plants Studies. Evaluation of selected transgenic papaya Carica papaya L lines for inheritance of resistance to papaya ringspot virus and horticultural traits.

Plant Biotechnology. Yeh SD, Gonsalves D. Evaluation of induced mutants of papaya ringspot virus for control by cross protection. Gonsalves D. Control of papaya ringspot virus in papaya: a case study. Annual Review of Phytopathology. Papaya ringspot virus-P: characteristics, pathogenicity, sequence variability and control. Molecular Plant Pathology. Papaya ringspot virus. In: Coronel RE, editor.

Wageningen, The Netherlands: Wageningen University; Khurana SMP. Studies on three virus diseases of papaya in Gorakhpur, India. Compendium of Tropical Fruit Diseases. Alvizo HF, Rojkind C. Resistencia al virus mancha anular del papayo en Carica cauliflora.

The first record of papaya ringspot virus-p in Australia. Australian Plant Pathology. Occurrence of the P strain of papaya ringspot virus in Japan. Annals of the Phytopathological Society. Australasian Plant Pathology. Viruses infecting papaya Carica papaya L. Plant Viruses. Potyviral HC-Pro: a multifunctional protein. Journal of General Virology. Mutations in the HC-Pro gene of zucchini yellow mosaic potyvirus: effects on aphid transmission and binding to purified virions.

Pirone TP, Blanc S. Helper-dependent vector transmission of plant viruses. CP-transgenic and non-transgenic approaches for the control of papaya ringspot: current situation and challenges. Transgenic Plant Journal. Papaya Carica papaya L. Tree and Forestry Science and Biotechnology. Horovitz S, Jimenez H. Cruzamientos interspecificos y intergenericos in Carica ceas y sus implicaciones fitotecnicas.

Agronomia Tropical Maracay ; 17 — Fuchs M, Gonsalves D. Safety of virus-resistant transgenic plants two decades after their introduction: lessons from realistic field risk assessment studies. Baulcombe DC. RNA as a target and an initiator of post-transcriptional gene silencing in trangenic plants. Plant Molecular Biology. The Plant Health Instructor. Tecson Mendoza EM, C. Laurena A, Botella JR. Recent advances in the development of transgenic papaya technology.

Biotechnology Annual Review. Yeh S-D, Gonsalves D. Translation of papaya ringspot virus RNA in vitro: detection of a possible polyprotein that is processed for capsid protein, cylindrical-inclusion protein, and amorphous-inclusion protein. Potyvirus proteins: a wealth of functions. Virus Research. A viral suppressor of gene silencing in plants.

Long-distance movement and replication maintenance functions correlate with silencing suppression activity of potyviral HC-Pro. Plant viral synergism: the potyviral genome encodes a broad-range pathogenicity enhancer that transactivates replication of heterologous viruses.

Plant Cell. Mapping of an RNA binding domain. Nucleic Acids Research. With the decline in papaya production on Oahu due to both PRSV and encroaching urbanization, the Puna district on the island of Hawaii became the major production centre. In this buffer zone, only occasional backyard or homeowner plants were noted, and remained PRSV free. Within 3 years, commercial production in Puna was no longer possible Fig. In this way, papaya production on the island of Hawaii was partially spared the total impact of PRSV, as production declined from 23 tonnes to 11 tonnes from to As the PRSV epidemic played out in Puna, efforts to develop a solution were well underway, having been initiated about 6 years earlier.

The CP gene construct was originally designed with the concept that protein expression was required for resistance. Evaluation of transgenic papaya for PRSV resistance. The results of the field trial were excellent and clearly demonstrated the potential value of transgenic papaya Fig. Fruit production data of Rainbow and SunUp in field tests showed that the yields were at least three times higher than the industry average while maintaining the percentage soluble solids above the minimum requirement for commercial fruits Ferreira et al.

In each view the susceptible Sunrise variety is shown on the left and resistant transgenic Rainbow on the right. The deregulation of Hawaiian transgenic papaya has been previously reviewed Gonsalves, ; Gonsalves et al. At present, transgenic papaya is widely sold in Hawaii and exported to the mainland US and Canada. This is perhaps a good model of engineered resistance in papaya for disease control, and biotechnology and technology transfer to other regions.

However, because the PRSV population in Hawaii is relatively homogeneous, the papaya industry in Hawaii is in a precarious position should resistance breakdown occur due to the emergence or arrival of divergent PRSV strains. Greenhouse inoculation studies by Tennant et al. R 1 plants were resistant to isolates from Hawaii but susceptible to PRSV strains occurring in other countries.

These results suggest that doubling transgene dosage will broaden transgenic resistance Tennant et al. Table is modified from Tennant et al. Comparison of the CP gene sequences from the various PRSV isolates suggested that resistance is positively correlated with the degree of homology between the CP of the infecting virus and the transgene. CP expression data from tested transgenic papaya plants were consistently lower in homozygous SunUp than hemizygous Rainbow.

These results showed clearly and consistently higher transcription in homozygous SunUp than in hemizygous Rainbow plants. In another study by Souza et al.

This requirement for transgene homology limits the applicability of transgenic resistance in different geographical regions that may harbour PRSV strains which are molecularly diverse. Although there appears to be a strong relationship between transgene and challenge virus CP gene homology for resistance to be expressed, other factors also influence the host's response.

Other studies have shown that the absence of transgene homology with the challenge virus CP gene does not always correlate with ability of a PRSV strain to breakdown resistance in transgenic papaya Chen et al.

This observation suggests that the breakdown of the transgenic resistance was not correlated with the sequence divergence between the infecting virus and the transgene. It would therefore be important to develop transgenic papaya that could mitigate against the impact of these PRSV strains. Papaya ringspot virus belongs to one of the largest and most economically important plant virus groups.

This potential for resistance breakdown suggests that it is important to monitor the PRSV population for its diversity and the arrival or emergence of new and more virulent strains in nature. The recent increase in cumulative data on PRSV gene sequences, including analyses on isolate variability and phylogenetic relationships between different geographical isolates will be helpful for devising effective PRSV management strategies such as design for the most effective transgene for specific regions.

In fact, evidence that transgenes could only protect against closely related virus strains stimulated the development of a next generation of transgenics that used a new approach of combining different transgene sequences to produce plants that are resistant to multiple viruses or virus isolates. Advances in our basic knowledge of pathogenicity and infectivity determinants of PRSV, the mechanism of gene silencing and gene silencing suppression in relation to transgenic resistance and its breakdown should also contribute to transgene design and other viral resistance strategies.

However, observations soon showed that the resistance of transgenic papaya, which was nearly all Rainbow, held up under conditions of very high PRSV inoculation pressure. The resistance of the transgenic papaya under rather strong disease pressure allowed farmers to directly reclaim their farms without first clearing their land of all infected papaya trees.

Common scenarios were to grow transgenic plants next to mature papaya plants, which were subsequently cut after the transgenic plants were established Fig. In all cases, the transgenic papaya remained virus-free.

Within a year after the release of the seeds, it was rather common to see many fields of healthy Rainbow Fig. PRSV infected papaya that were cut down in the foreground and healthy transgenic Rainbow papaya in the background. Picture taken in Green healthy transgenic Rainbow papaya growing among PRSV-infected trees in an abandoned papaya field.

By healthy fields of transgenic papaya were commonly seen as opposed to the period of where it was very difficult to find healthy papaya fields in Puna see Fig. Controlling PRSV. The field resistance of the transgenic papaya in Puna proved to be durable, a result that was not necessarily predictable given that greenhouse tests had shown Rainbow to be resistant to the several PRSV isolates from Hawaii but susceptible to a range of isolates from outside of Hawaii 9.

For example, isolates from Guam, Taiwan, and Thailand overcame the resistance of Rainbow. Recent studies in our laboratories and others have shown that the pathogen-derived resistance to plant viruses is due to the mechanism of post-transcriptional gene silencing or RNA-interference 8.

A practical consequence is that increasing the transgene dosage can lead to increased resistance. Thus, transgene dosage is the likely reason that SunUp shows broader resistance than Rainbow, in that SunUp is homozygous for the inserted coat protein gene, while Rainbow is hemizygous or has half the gene dosage of SunUp because it is an F1 hybrid between SunUp and the nontransgenic Kapoho.

The continued popularity of Rainbow points out that factors other than resistance play a large role in the commercial adoption of the transgenic papaya. While it would seem prudent that SunUp should be the cultivar of choice for ensuring the resistance to PRSV in Hawaii, the demand for Rainbow has grown because the industry and market prefer that cultivar.

Thus, Rainbow plantings are constantly being monitored for evidence of breakdown of resistance. Fortunately, in Puna and Oahu, the resistance has held up well under diverse conditions of plantings and disease pressure. Increased production of papaya.

The release of the transgenic papaya resulted in an increase of papaya production in Hawaii and Puna. The following observations were made for Puna up to the year Table 1. The production remained high for two years following the discovery of PRSV in Puna due to massive efforts to control the spread of the virus.

However, by papaya production in Puna had dropped to 39 million pounds and was down to 26 million pounds in when transgenic seeds of cultivars were released to farmers. Production of papaya in Puna increased starting in and peaked at 40 million pounds in with 35 million pounds being produced in The impact of the transgenic papaya in increasing papaya production in Puna is also seen by analyzing the relative bearing acres of Rainbow and the nontransgenic Kapoho Table 2.

In , Puna production was 26 million pounds from 1, acres of bearing Kapoho, since Rainbow had not yet produced mature fruit. Production dropped from 40 million pounds in to 36 million pounds in These data suggest that Rainbow accounts for at least half of the fresh fruit production in Puna.

Furthermore, production of similar amounts of papaya can be obtained with less acreage. This latter observation is attributed to the higher level of production of Rainbow compared to nontransgenic Kapoho. Table 2. Help in production of nontransgenic Kapoho in Puna. In fact, it is critical that Hawaii continues to produce nontransgenic papaya to supply the market in Japan, as will be discussed below.

Arguably, one of the major contributions that the transgenic papaya has made to the papaya industry is that of helping in the economical production of nontransgenic papaya 4. This has occurred in several ways.

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 reduction in virus inoculum allowed for strategic planting of nontransgenic papaya in areas that were free of infected plants and were not surrounded by areas of infected plants, such as had been present in In fact, the Hawaii Department of Agriculture HDOA instituted a plan in to ensure the production of nontransgenic papaya in the Kahuwai area of Puna by taking advantage of the natural reduction in inoculum pressure due to the large-scale plantings of Rainbow in Puna, the isolation of the proposed area from established papaya fields, and the fact that the prevailing winds in Kahuwai come from the ocean which borders the area 4.

Furthermore, growers were to monitor for infection and rogue infected plants quickly. This program successfully helped growers who followed the recommended practices to economically produce Kapoho without major losses from PRSV. Although definitive experiments have not been carried out, it seems that transgenic papaya can provide a buffer zone to protect nontransgenic papaya that are planted within the confines of the buffer.

The reasoning is that viruliferous aphids will feed on transgenic plants and thus be purged of virus before traveling to the nontransgenic plantings within the buffer. This approach also has the advantage that it allows the grower to produce transgenic and nontransgenic papaya in relatively close proximity.

Timely elimination of infected trees would need to be practiced to delay large-scale infection of the nontransgenic plants. Expanding papaya production areas and the diversification of cultivars available for Hawaii. Prior to the release of transgenic papaya, Oahu growers farmed only small plots of papaya due to the effect of PRSV on production.

Growers on Oahu enjoy a niche market, growing Rainbow papaya for residents in Honolulu and other urban areas of the island. The transgenic papaya has also allowed for the development of new cultivars to meet niche market needs on Oahu island. The new transgenic cultivar Laie Gold, which is a hybrid between Rainbow F2 and the nontransgenic Kamiya papaya also serves a niche market on Oahu island.

Since Rainbow F2 is not homozygous for the coat protein gene, Laie Gold needs to be micropropagated to achieve uniformity of production. The micropropagation of the papaya also has the added benefits of ensuring the production of only hermaphrodite plants demanded by the market, earlier and lower bearing trees with initially higher yields, and providing selected, superior clones that could result in improved quality and yield.

Since the introduction of transgenic papaya, the number of cultivars available to papaya growers in Hawaii has actually increased.