TRANSGENIC SWEET ORANGE IMMUNE TO CITRUS PSOROSIS VIRUS

REYES CA; DE FRANCESCO A; COSTA N; PLATA MI; GARCIA ML

Campinas, Brazil

Conferencia; XVIII Conference of the International Organization of Citrus Virologists (IOCV); 2010

IOCV

 Psorosis is an important disease causing significant economic losses in the citrus region of Argentina. There is no natural resistance cultivar against its causal agent, Citrus psorosis virus (CPsV). In order to obtain resistant plants, several transgenic lines were selected after transformation with fragments of the CPsV genome (pathogen derived resistance). We have applied the Agrobacterium transformation and the mechanism of post- transcriptional gene silencing (PTGS) as the strategy to make the plant resistant to the virus. The construct used for transformation generates in the plant cell an RNA transcript which adopts a hairpin RNA structure (intron hairpin RNA, ihpRNA). This transcript is the inducer of the PTGS, degrading the viral RNAs into the cell by a specific recognition. Different fragments of CPsV genome were used for transformation, generating ihp54K and ihp24K lines, which were susceptible, and the ihpCP lines resulting highly resistance. All the lines were challenge with the virus by graft-transmission, and symptoms observation was done during 4 months, and more than one year in some cases. Molecular analyses were carrying out by RT-PCR and TAS-ELISA for virus multiplication and Northern blot to detect viral RNA and presence of the siRNA generated by PTGS mechanism. In lines ihpCP did not show any symptoms, the virus was not detected and siRNA were present. These immune lines will be challenged under field conditions in order to observe the resistance stability in front of this long and severe disease.