Since 1992, Papaya ringspot virus (PRSV) destroyed nearly all of the papaya hectarage in the Puna district of Hawaii, where 95% of Hawaii's papayas are grown. Two field trials to evaluate transgenic resistance (TR) were established in Puna in October 1995. One trial included the following: SunUp, a newly named homozygous transformant of Sunset; Rainbow, a hybrid of SunUp, the nontransgenic Kapoho cultivar widely grown in Puna, and 63-1, another segregating transgenic line of Sunset. The second trial was a 0.4-ha block of Rainbow, simulating a near-commercial planting. Both trials were installed within a matrix of Sunrise, a PRSV-susceptible sibling line of Sunset. The matrix served to contain and trace pollen flow from TR plants, and as a secondary inoculum source. Virus infection was first observed 3.5 months after planting. At a year, 100% of the non-TR control and 91% of the matrix plants were infected, while PRSV infection was not observed on any of the TR plants. Fruit production data of SunUp and Rainbow show that yields were at least three times higher than the industry average, while maintaining percent soluble solids above the minimum of 11% required for commercial fruit. These data suggest that transgenic SunUp and Rainbow, homozygous and hemizygous for the coat protein transgene, respectively, offer a good solution to the PRSV problem in Hawaii.

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Inserts and insert sites in transgenic, papaya ringspot virus (PRSV)-resistant commercial papaya Rainbow and SunUp, were characterized as part of a petition to Japan to allow import of fresh fruit of these cultivars from the U.S. and to provide data for a larger study aimed at understanding the global impact of DNA transformation on whole genome structure. The number and types of inserts were determined by Southern analysis using probes spanning the entire transformation plasmid and their sequences determined from corresponding clones or se-HI 96701, USA quence reads from the whole-genome shotgun (WGS) sequence of SunUp papaya. All the functional transgenes, coding for the PRSV coat protein (CP), neophosphotransferase (nptII) and β-glucuronidase (uidA) were found in a single 9,789 basepair (bp) insert. Only two other inserts, one consisting of a 290 bp nonfunctional fragment of the nptII gene and a 1,533 bp plasmid-derived fragment containing a nonfunctional 222 bp segment of the tetA gene were detected in Rainbow and SunUp. Detection of the same three inserts in samples representing transgenic generations five to eight (R5 to R8) suggests that the three inserts are stably inherited. Five out of the six genomic DNA segments flanking the three inserts were nuclear plastid sequences (nupts). From the biosafety standpoint, no changes to endogenous gene function based on sequence structure of the transformation plasmid DNA insertion sites could be determined and no allergenic or toxic proteins were predicted from analysis of the insertion site and flanking genomic DNA.

The virus-resistant, transgenic commercial papaya Rainbow and SunUp (Carica papaya L.) have been consumed locally in Hawaii and elsewhere in the mainland United States and Canada since their release to planters in Hawaii in 1998. These papaya are derived from transgenic papaya line 55-1 and carry the coat protein (CP) gene of papaya ringspot virus (PRSV). The PRSV CP was evaluated for potential allergenicity, an important component in assessing the safety of food derived from transgenic plants. The transgene PRSV CP sequence of Rainbow papaya did not exhibit greater than 35% amino acid sequence homology to known allergens, nor did it have a stretch of eight amino acids found in known allergens which are known common bioinformatic methods used for assessing similarity to allergen proteins. PRSV CP was also tested for stability in simulated gastric fluid and simulated intestinal fluid and under various heat treatments. The results showed that PRSV CP was degraded under conditions for which allergenic proteins relative to nonallergens are purported to be stable. The potential human intake of transgene-derived PRSV CP was assessed by measuring CP levels in Rainbow and SunUp along with estimating the fruit consumption rates and was compared to potential intake estimates of PRSV CP from naturally infected nontransgenic papaya. Following accepted allergenicity assessment criteria, our results show that the transgene-derived PRSV CP does not pose a risk of food allergy.