Virus Resistance Mediated By Inverted Repeats Derived From 5' And 3' Ends Of The Coat Protein Gene Of Potato Virus Y

As a genome defense mechanism, RNA silencing has been termed as posttranscriptional gene silencing (PTGS) in plants, RNA interference in animals and quelling in fungi. Recent studies have revealed that this mechanism is conserved among various eukaryotic organisms to counter the proliferation of alien sequences, such as transposable elements, transgenes and viruses, by specifically degrading mRNAs homologous to the target genes. RNA-mediated virus resistance is induced by transgenes derived from genes of viral and regarded as a potential strategy with application value in plant resistance breeding against viruses, which has the advantages of extreme resistance (immune), high biosafety and long duration. Double-stranded RNA (dsRNA) from a variety of sources, (such as transgenes, RNA viruses, transposons, etc.) has been shown to be the key trigger molecules for RNA silencing in various organisms. In plants, transformation of IR to hosts is considered as a particularly effective way to induce gene silencing.In this study we constructed two shorter hpDNAs derived from 5' end of PVY~N-CP with the stem length of 98bp-stem and 50bp-stem (50bp-loop), and one from 3' ends of PVY~N-CP with the stem length of 50bp-stem (50bp-loop), respectively, to compare the effectiveness of the two hpDNAs on the induction of RNA-mediated virus resistance, especially to examine if the hpDNA with 50bp-stem is long enough to induce PTGS. The results of this study provided useful information for the shortest effective fragment of a given viral gene to induce viral resistance, and consequently might be valuable as a strategy to produce transgenic plants with multi-virus resistance. The main results presented in this thesis are as follows:1. Inverted repeats cDNA F1F2, F3F4 and F5F6 were cloned and inserted between the 35S promoter and nos tenninator sequences of the binary vector to form pROK-5'98IR, pROK-5'50IRå’ŒpROK-3'50IR.2. The three recombinant plasmids pROK-5'98IR, pROK-5'50IR, pROK-3'50IR together with recombinant plasmids pROK-3'98IR and pROKII...