Our research interests are focused in the role of RNA interference (RNAi) mechanism in which small interfering RNAs (siRNAs) induce gene silencing as part of RNA-induced silencing complexes (RISCs). This silencing mechanism is remarkably conserved within organisms and in Arabidopsis thaliana a nuclear siRNA-dependent pathway directing DNA methylation and histone methylation transcriptionally silences repetitive DNA sequences. This pathway involves two nuclear RNA polymerase, pol IV and pol V, RNADEPENDENT RNA POLYMERASE 2 (RDR2), DICER-LIKE 3 (DCL3), ARGONAUTE 4 (AGO4), the chromatin remodeler, DRD1, the de novo cytosine methyltransferase, DRM2. Previous cytological and biochemical analysis strongly suggests a stepwise model for nuclear siRNA biogenesis and target locus chromatin modifications that involves multiple sub-nuclear domains. In the model, effector complex assembly appears to take place within a nuclear domain distant from the site of effector action at target loci, indicating that sub-nuclear trafficking is critical for siRNA-mediated heterochromatin formation. A major emphasis in our research is to determine the subnuclear compartmentalization, assembly and mode of action of RNAi-mediated effector complexes that direct chromatin modifications to specific target loci. Molecular and biochemical techniques are being used in combination with advanced live-cell imaging methods to address those specific goals. Our long-term goal is aimed at understanding whether A. thaliana RNAi-effector complexes work independently or in cooperation with chromatin-modifier proteins in mediating target locus chromatin modifications and gene silencing.

• Selected Publications

Arabidopsis thaliana interphase nucleus showing the spatial distribution of RDR2 (in red) and AGO4 (in green).