Influence of Coat Protein Transgene Copy Number on Resistance in Transgenic Line 63-1 against Papaya Ringspot Virus Isolates

in HortScience

Line 63-1 is a `Sunset'-derived transgenic papaya expressing the coat protein (CP) gene from a mild mutant of a Hawaiian isolate of Papaya ringspot virus (PRSV). Previous work showed that line 63-1 R1 plants exhibited a range of resistance to severe PRSV isolates from Hawaii (HA), Jamaica (JA), Thailand (TH), and Brazil (BR). Genetic and molecular data obtained in this study confirm that line 63-1 has two CP transgene insertion sites; segregation analysis shows that the CP and the npt II genes are present at both loci. To study the potential effect of gene dosage on resistance, various populations of R1, R2, and R3 seedlings were challenged by PRSV HA, BR, and TH. A R1 population obtained by self-pollination of line 63-1 hermaphrodite R0 plant exhibited resistance to all three isolates. The percentage of plants resistant to all three PRSV isolates increased in 63-1-derived populations as a result of recurrent selection. Additional genetic studies demonstrate that the number of resistant plants in a 63-1-derived population is directly correlated with the number of plants with multiple transgene copies. We conclude that transgene dosage plays a major role in affecting the resistance of 63-1 to PRSV isolates from various geographical locations.

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Contributor Notes

Corresponding author. Current mailing address: Embrapa Genetic Resources and Biotechnology, Parque Estação Biológica, CP 02372, Final Av. W5 Norte, Brasília, DF 70770-900, Brazil; e-mail msouza@cenargen.embrapa.br.

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