S.07. Engineering transgenic resistance against tungro viruses in rice using multiple approaches

Rice tungro bacilliform virus (RTBV), a double-stranded DNA virus and Rice tungro spherical virus (RTSV), a single-stranded RNA virus, jointly infect rice to cause the tungro disease. RTBV and RTSV, often referred to as tungro viruses are transmitted as a complex by the specific insect vector, Green Leafhopper (GLH), Nephotettix virescens. To obtain transgenic resistance against the tungro viruses, multiple approaches, both protein-mediated as well as RNA-mediated were attempted. Protein-mediated approaches included expression of the coat proteins of RTBV or RTSV. Approaches using RNA to target the RTBV transcript used anti-sense as well as RNA-interference steps. Transgenic rice plants were raised with all the above constructs, using Agrobacterium-mediated transformation. A total of 20 independent transgenic events were characterized by Southern analysis, containing from 1–3 copies of the transgene. Majority of the transgenes were found to be expressing at moderate levels by northern and western analyses. The RNA-interference constructs were found to be lacking detectable transcripts of the transgene, at the same time, forming 22–24 nucleotide si-RNA. This indicated activation of the RNA-interference pathway. When the transgenic plants were challenged by viruliferous GLH, most of them showed either lower titers of RTBV/RTSV or delayed accumulation as compared to non-transgenic control plants, when monitored at regular intervals for 2–3 months post-inoculation. Many of the inoculated transgenic plants also showed little or no tungro symptoms, whereas non-transgenic control plants were fully symptomatic. Details of the results will be presented.