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item Gonsalves, Dennis

Submitted to: Brazilian Journal of Agricultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2004
Publication Date: 5/20/2005
Citation: Souza, M., Gonsalves, D. 2005. Sequence similarity between the viral CP gene and the transgene in transgenic papayas. Pesc. Agrotech. Bras., Brasilia. 40(5):479-486.

Interpretive Summary: Transgenic ‘Rainbow’ contains the coat protein gene of papaya ringspot virus HA (PRSV HA), which was isolated from Hawaii. Rainbow is the most widely planted transgenic papaya in Hawaii and is highly resistant to PRSV HA. Research had shown that the sequence of the coat protein gene of PRSV plays an important role in breaking down resistance of ‘Rainbow’ papaya. A hybrid virus was constructed with genome of PRSV HA except that the coat protein gene of PRSV from Thailand was substituted for the coat protein gene of PRSV HA. The hybrid virus was able to overcome the resistance of ‘Rainbow’. These results reinforce the potential that the transgenic papaya in Hawaii could be overcome by strains of PRSV which may be introduced into Hawaii.

Technical Abstract: The Papaya ringspot virus (PRSV) coat protein transgene present in ‘Rainbow’ and ‘SunUp’ papayas disclose high sequence similarity (>89%) to the cp gene from PRSV BR and TH. Despite this, both isolates are able to break down the resistance in ‘Rainbow’, while only the latter is able to do so in ‘SunUp’. The objective of this work was to evaluate the degree of sequence similarity between the cp gene in the challenge isolate and the cp transgene in transgenic papayas resistant to PRSV. The production of a hybrid virus containing the genome backbone of PRSV HA up to the Apa I site in the NIb gene, and downstream from there, the sequence of PRSV TH was undertaken. This hybrid virus, PRSV HA/TH, was obtained and used to challenge ‘Rainbow’, ‘SunUp’, and an R2 population derived from line 63-1, all resistant to PRSV HA. PRSV HA/TH broke down the resistance in both papaya varieties and in the 63-1 population, demonstrating that sequence similarity is a major factor in the mechanism of resistance used by transgenic papayas expressing the cp gene. A comparative analysis of the cp gene present in line 55-1 and 63-1-derived transgenic plants and in PRSV HA, BR, and TH was also performed.