Combined expression of p20 and p23 proteins from Citrus tristeza virus show enhanced local silencing suppressor activity
Viruses developed a strategy to counter-defence the posttranscriptional gene silencing mechanism (PTGS) based on the activity of silencing suppressor proteins. Citrus tristeza virus (CTV), a member of the genus Closterovirus, has two suppressor proteins (p20 and p23) that target the local RNA silencing response of the host. In GFP transient co-expression assays performed on Nicotiana benthamiana 16C plants, local suppressor activity of p23 and p20 was similar. Co-expression of both proteins from a mild or a stem pitting CTV isolate showed stronger local suppression activity than either suppressor alone, with an increased GFP transcript level six- (for Gp M) to nine-fold (for Gp 3a) higher than non-inoculated 16C plants, in parallel with low accumulation of siRNAs. Further, GFP brightness of leaves infiltrated with Agrobacterium cultures at an OD600 of 0.5 was comparable to those infiltrated with OD600 0.25. These findings indicate that combined action of p20 and p23 proteins results in enhanced suppressor activity.
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