It’s often easiest to put together a jigsaw puzzle by finding the corner pieces first, then working on the borders before moving on to what’s happening in the center. A similar approach to solving the transcriptional gene silencing (TGS) and RNA-directed DNA methylation (RdDM) mechanisms in Arabidopsis has identified a protein, RDM1, which seems to be a “corner piece” in the RdDM puzzle.
A team of scientists at UC Riverside came across RDM1 while screening for gene mutations that play a role in the DNA methylation of certain loci, and regulate TGS. A few experiments later, they found out a lot more about their new puzzle piece:
- RDM1 loss-of-funtion mutants lower siRNA accumulation, reduce DNA methylation and release TGS at RdDM targets.
- It binds single-stranded methylated DNA, suggesting a potential mechanism for RdDM complex targeting to methylated DNA via RDM1.
- It co-localizes with known RdDM effector complex members RNApolII, AGO4, and DRM2 in the nucleus.
- RDM1 may also function with RNA pol V at RdDM target sites, but only outside of the nucleus.
These findings could be a missing link between siRNA production and de novo DNA methylation in plants.
Still puzzled? Check out the details for yourself at Nature, April 2010.