Development of broad spectrum virus resistance in plants

Viruses are widely accepted as the major class of plant pathogens responsible for significant crop losses that reduce the quality and quantity of product biomass. The objective of this study is to minimize yield losses by developing two efficient approaches based on (1) pathogen targeted resistance and (2) RNA interference (RNAi). In the first approach, the oligoadenylate synthetase (OAS), a mammalian antiviral pathway, was utilized to develop broad spectrum virus resistance in plants. It is composed of two enzymes - a 2,5A synthetase and a 2,5A-dependent RNase L. Suitability of the antiviral pathway was evaluated in transgenic tobacco (N. tabacum and N. benthamiana), soybeans and wheat plants. Tobacco plants expressing the OAS transgenes showed resistance to Tobacco mosaic virus (TMV), Tobacco etch virus (TEV) and Cucumber mosaic virus (CMV D and Y strains). Similarly, transgenic soybean carrying the OAS system was evaluated for resistance against Soybean mosaic virus (SMV) and Bean pod mosaic virus (BPMV), and transgenic wheat against Wheat streak mosaic virus (WSMV). These results showed that the system has the potential to provide broad spectrum resistance against different viruses and can confer resistance to different crops. The second approach utilizes RNA interference, a widely used method for down regulating targeted transcripts and developing disease-resistant plants. RNAi is a type of post-transcriptional gene silencing (PTGS) that relies on the presence of dsRNA to induce silencing complex leading to the degradation or inactivation of the target mRNA. A direct repeat induced gene silencing (DRIGS) system was used as a tool for developing broad spectrum virus resistance in plants. Short viral fragments from different viruses were fused in the silencing locus of the DRIGS vector and transformed into Arabidopsis, N. tabacum and N. benthamiana. Virus specific siRNAs were detected in the transgenic plants. TMV and TEV inoculated transformed plants remained symptomless and virus-free. These results show that the system simultaneously provides broad spectrum resistance to multiple viruses