|Souza Junior, Manoel|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2005
Publication Date: 12/20/2005
Citation: Souza Junior, M.T., Tennant, P., Gonsalves, D. 2005. Influence of Coat Protein Transgene Copy Number on Resistance in Transgenic Line 63-1 Against Papaya Ringspot Virus Isolates. Hortscience. 40(7). P2083-2087. Interpretive Summary: Papaya ringspot virus (PRSV) causes the most important viral disease of papaya worldwide. A genetically engineered papaya (line 55-1) resistant to PRSV was developed and helped to save the papaya industry in Hawaii. In this report we analyzed the resistance of another genetically engineered line developed for Hawaii, line 63-1. Unlike line 55-1, line 63-1 has two coat protein gene inserts. This study shows that the number of coat protein inserts that are in the transgenic papaya influences the resistance against PRSV isolates from Hawaii, Brazil, and Thailand. Generally, plants with both inserts provided the best resistance against a range of PRSV isolates. This information will help breeders formulate a sound strategy for developing varieties from line 63-1 that have a wide range of resistance to PRSV isolates.
Technical Abstract: 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 confi rm 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.