Evaluation of Plum Pox Virus (PPV) CP and P1 Constructs on Sharka Resistance in Plum (Prunus domestica)

Genetically engineered Plum pox virus (PPV) (sharka) resistance was studied in the woody perennial Prunus domestica plum using transgenic plants harbouring a combination PPV-P1+PPV-coat protein (CP) gene construct. Resistance was studied in genetically engineered (GE) and control scions grafted onto GF 8.1 Prunus mariana rootstocks that were graft-inoculated with PPV. Early responses of the GE scions to PPV infection were similar and ranged from symptomless, to very mild symptoms, to the appearance of a few necrotic spots on leaves closest to the graft areas. While susceptible GE and non-GE control plants with time displayed systemic sharka symptoms, some clones displayed a high level of resistance similar to that seen in 'HoneySweet' plum. Molecular studies demonstrated that small interfering RNAs (siRNAs) produced by these plants play an important role in host defence in response to PPV. Regardless of the PPV-derived transgene insert, our results indicate that expression of PPV resistance in these transgenic plums is correlated with the accumulation of PPV-specific siRNAs derived from the transgene transcripts engineered into the plum genome.