|Hily, Jean Michel|
Submitted to: Virus Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2007
Publication Date: 12/11/2007
Citation: Kundu, J., Briard, P., Hily, J., Ravelonandro, M., Scorza, R. 2007. Role of the 25-26 nt siRNA in the resistance of transgenic Prunus domestica graft inoculated with plum pox virus. Virus Genes. 36:215-220. Interpretive Summary: Plum pox virus is a serious exotic disease of plum that has recently been discovered in the U.S. Through genetic engineering, we have developed a plum variety ('HoneySweet') that is a highly resistant plum pox virus. We found that 'HoneySweet' is resistant to plum pox virus through the process of gene silencing and produces small RNA molecules that are responsible for resistance. In the work reported here, we show that a small RNA of a particular size (~26 nucleotides) is the small RNA responsible for plum pox virus resistance in 'HoneySweet'. This information will be useful in the future for developing additional genetically engineered virus resistant plants and also, give us new information on the natural mechanisms of virus resistance in plums.
Technical Abstract: The reaction of a genetically engineered plum clone (C5) resistant to plum pox virus (PPV) to graft inoculation with the virus was evaluated. The resistance in this clone has been demonstrated to be mediated through post-transcriptional gene silencing (PTGS). A single C5 plant out of 30 plants inoculated with PPV M strain by double chip-budding showed a mild diffuse mosaic 'Sharka' symptom at the bottom section of the scion. The upper leaves of this PPV infected C5 plant remained without symptoms and were confirmed as virus-free by DAS-ELISA and RT-PCR. RNA silencing associated small interfering RNA duplex, siRNA (21-26 nt) was detected in non-inoculated C5 plants and in the inoculated but virus free portion of the C5 plant under evaluation. In the PPV infected portion of the C5 plant and in C6 PPV susceptible plants, only the ~ 21-22 nt siRNAs were detected. Cytosine-methylation was confirmed in C5 plants, both uninfected and showing PPV symptoms. The 25-26 nt long class siRNA normally present in C5 was absent in PPV infected C5 tissues confirming the critical role of the 25-26 nt long siRNA in the resistance of clone C5 to PPV infection. We also show that this PPV infection was limited and transient. It was only detected in one plant at one of four post-dormancy sampling dates and did not appear to affect the overall PPV resistance of the C5 clone.