Isolation and Characterization of an Anti-viral RISC in Plants
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As a defense against viral infection, plants are only very recently thought to use an RNA-induced silencing complex (RISC) as part of the RNA interference (RNAi) pathway to target and cleave viral RNA. To counteract this, some viruses have evolved proteins to inhibit RISC-mediated activity, thus ensuring their continued virulence. This research focused on the elucidation and analysis of anti-viral RISC in plants, to gain an understanding of how both the plant defense and countering viral mechanisms operate at the molecular level. A virus-host model system was used to examine this; Nicotiana benthamiana plants were infected with Tomato bushy stunt virus (TBSV) and time was allowed for RISC to target and cleave the viral RNA. If the TBSV defense protein, called P19, was present, the virus was not degraded by RISC and infection culminated in the death of the plant. When the plants were instead inoculated with a mutant of the virus, in which P19 was not expressed, RISC cleared the viral RNA and the plant survived the infection. This agrees with the model that RISC can (be programmed to) act as an anti-TBSV complex. To examine the composition of the anti-TBSV RISC, plant proteins from both scenarios (with the presence or absence of P19) were subjected to various biochemical analyses and purification techniques. Proteins most closely associated with RISC activity in vitro (degradation of viral RNA in the test tube) were purified toward determining their identity. Future experiments are planned to examine if the antiviral RISC proteins are unique to TBSV infected plants or whether they are also associated with other virus infections.
Ciomperlik, Jessica (2006). Isolation and Characterization of an Anti-viral RISC in Plants. Available electronically from