A novel function for a ubiquitous plant enzyme pectin methylesterase: the enhancer of RNA silencing.

Co-agroinjection of Nicotiana benthamiana leaves with the pectin methylesterase (proPME) gene and the TMV:GFP vector resulted in a stimulation of virus-induced RNA silencing (inhibition of GFP production, virus RNA degradation, stimulation of siRNAs production). Conversely, co-expression of TMV:GFP with either antisense PME construct or with enzymatically inactive proPME restored synthesis of viral RNA. Furthermore, expression of proPME enhanced the GFP transgene-induced gene silencing accompanied by relocation of the DCL1 protein from nucleus to the cytoplasm and activation of siRNAs and miRNAs production. It was hypothesized that DCL1 relocated to the cytoplasm may use as substrates both miRNA precursor and viral RNA. The capacity for enhancing the RNA silencing is a novel function for the polyfunctional PME.