Grapevine Biotechnology

Induction of virus resistance by transgene-induced "genes silencing"

Plant-infecting viruses consist of a nucleic acid molecule - in most cases there are one or more single-stranded RNA molecules - packed in a coat protein. Viruses do not have their own metabolism and are thus dependent on the protein-synthesizing tools of the host organism. Investigations of mechanisms for virus resistance in plants led to the discovery of the phenomenon of 'gene silencing' or 'RNA silencing'. This mechanism, which is not limited to plants, has its biological meaning in the control of gene expression, in the control of transposon elements (jumping genes) and in the control and/or degradation of aberrant and penetrating RNA, and thus in resistance against viruses. The mechanism is sequence-specific. Within the framework of the research project at AlPlanta, isolates of viruses relevant to the Fanleaf disease (GFLV, ArMV and RpRSV) were collected from different viticulture regions of Europe and sequence comparisons of the viral RNA were carried out. In this way, highly conserved regions could be determined that exhibited an approx. 90% similarity in the nucleotide sequence within the virus isolates. Viral sequence-derived DNA fragments were produced, cloned into a gene construct and transferred by Agrobacteria into N. benthamiana as a test system as well as into grapevines. The intended strategy is to induce a sequence-specific defence mechanism in the plant, leading to the processing of transgene-derived RNA as well as of homologous sequences of appropriate viral RNA. Thus a defence mechanism is already specifically established against the appropriate viruses before possible infection.

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