RNA interference-mediated gene knockdown within specific cell types.

In plants, RNA interference (RNAi)-induced gene silencing can spread from the initiation site to nearby cells. The silencing signal moves from cell-to-cell through plasmodesmata and, over long distances, through the phloem. In this study, we employed a nuclear-localized GFP fusion protein to visualize the pattern of gene silencing induced by three different transgenes expressing double-stranded RNA (dsRNA) in Arabidopsis root tips. In all cases, we found that dsRNA-induced silencing did not spread from the silencing initiation site to adjacent cells. In the first set of experiments, in a transgenic background expressing nuclear-localized GFP within a contiguous cell layer that included endodermis, cortex/endodermis (joint) initial (CEI) cells and the quiescent center (QC) cells, expression of the marker gene was silenced specifically in the QC cells without affecting gene expression in the adjacent CEI and endodermal cells. The next two sets of experiments examined the knockdown of two endogenous genes. We observed that silencing was completely restricted to the QC and endodermal cells within which the dsRNA transgenes were expressed. Overall, these results accentuate one important aspect of RNAi-induced gene silencing, that it can be cell autonomous, and demonstrated the feasibility of selective gene knockdown within specific cell types.