Multiple resistance to PVY [potato virus Y] by transformation of Solanaceous crops with engineered viral genes : final report covering period October 1993-February 1998

In particular, moderate to heavy yield losses are caused in these species by potato virus Y (PVY). The overall aim of this project was to engineer resistance to PVY in these crops by introducing viral sequences that would potentially interfere with PVY replication. Two complementary strategies were attempted, as described below. The first strategy was to integrate a defective viral replicase gene in the plant host genome. This approach capitalizes on the currently available information regarding the genomic composition of PVY. A self-processing protease- replicase-coat protein gene complex of PVY was cloned and its putative active site (the GDD motif) was modified by site- directed mutagenesis of the cloned gene complex. Subsequently, the modified replicase gene with its authentic flanking sequences was introduced into Solanaceous plants, as part of a self- catalytic complex that also contains a viral proteolytic peptide that is responsible for the in-vivo processing of the PVY polyprotein. Transgenic tobacco plants harboring these constructs were evaluated for viral resistance. The results do not support evidence for substantial resistance. Full evaluation of this approach awaits future work. In the second approach, antisense oligonucleotide sequences (AsO) to untranslated regions (UTR) of the PVY genome were synthesized and tested for their inhibitory effects on the in-vitro translation of the viral genome. AsO that proved effective were subsequently introduced into Solanaceous species. Promising levels of resistance were detected in transgenic tobacco harboring these constructs. Future work is aimed at confirming and expanding these results. The intensive training of young Kazakh scientists in the participating Israeli laboratories was considered an additional goal and an imperative component of this program. Three staff members of the Kazakh group spent a total of 20 months in the Israeli counterpart groups. The trainees extensively practiced techniques for isolation and cloning of viral genes and their transformation into plants. The capabilities of the Kazakh laboratory were substantially enhanced in the field of transgenic breeding for viral resistance, as well as in managerial aspects related to the participation in international research programs. (Author abstract)