DCL3 (Dicer-like 3) is a plant gene that encodes a ribonuclease III enzyme involved in the RNA-directed DNA methylation (RdDM) pathway, a plant-specific mechanism of transcriptional gene silencing.[1][2] DCL3 processes double-stranded RNA (dsRNA) precursors into 24-nucleotide small interfering RNAs (siRNAs) that guide epigenetic modification of target genomic loci.[1]
DCL3 is one of several Dicer-like (DCL) proteins encoded in plant genomes. Unlike DCL1, which primarily generates microRNAs, and DCL4, which produces 21-nucleotide siRNAs, DCL3 is specialized for the biogenesis of 24-nucleotide siRNAs that function in heterochromatic silencing and transposon repression.[2]
Function
In plants, the RNA-directed DNA methylation (RdDM) pathway mediates transcriptional silencing of repetitive elements and transposable elements through small RNA–guided epigenetic modification. DCL3 plays a central role in this pathway by generating 24-nucleotide siRNAs from endogenous dsRNA substrates.[3]
These dsRNA precursors are derived primarily from transcripts produced by RNA polymerase IV at heterochromatic loci. The single-stranded RNA products of Pol IV are converted into double-stranded RNA by RNA-dependent RNA polymerase 2 (RDR2). DCL3 then cleaves these dsRNA molecules into 24-nt siRNAs.[3]
The resulting siRNAs are incorporated into the Argonaute 4 (AGO4) protein. AGO4-associated siRNAs base-pair with scaffold transcripts generated by RNA polymerase V, facilitating recruitment of domains-rearranged methylase 2 (DRM2). This process results in cytosine DNA methylation and transcriptional repression of the target locus.[3]
Evolutionary history
DCL3 arose as a specialized paralog within the plant Dicer-like (DCL) gene family during early land plant evolution.[1][2][4] Phylogenetic analyses indicate that DCL3 is present in bryophytes and vascular plants, consistent with the early establishment of RNA-directed DNA methylation (RdDM) pathways in terrestrial plant lineages.[2][4] In contrast to animal Dicer proteins, which primarily generate microRNAs and siRNAs involved in post-transcriptional regulation, plant DCL3 became functionally specialized for the production of 24-nucleotide siRNAs associated with transcriptional gene silencing and heterochromatin formation.[1]
The emergence of DCL3 coincided with the evolution of plant-specific RNA polymerases, including RNA polymerase IV and RNA polymerase V, which are central to the RdDM pathway.[4] This coordinated expansion of silencing machinery enabled plants to establish robust epigenetic regulation of transposable elements and repetitive DNA. Comparative genomic studies suggest that the 24-nucleotide siRNA pathway is broadly conserved across land plants, reflecting an early and stable integration of DCL3-mediated silencing into plant genome defense and epigenetic regulation systems.[1]
References
- ^ a b c d e Law JA, Jacobsen SE (2010). “Establishing, maintaining and modifying DNA methylation patterns in plants and animals”. Nature Reviews Genetics. 11 (3): 204–220. doi:10.1038/nrg2719. PMID 20142834.
- ^ a b c d Matzke MA, Mosher RA (2014). “RNA-directed DNA methylation: an epigenetic pathway of increasing complexity”. Nature Reviews Genetics. 15 (6): 394–408. doi:10.1038/nrg3683. PMID 24805120.
- ^ a b c Wang Q, Xue Y, Zhang L, Zhong Z, Feng S, Wang C, et al. (November 2021). “Mechanism of siRNA production by a plant Dicer-RNA complex in dicing-competent conformation”. Science. 374 (6571): 1152–1157. Bibcode:2021Sci…374.1152W. doi:10.1126/science.abl4546. PMC 8682726. PMID 34648373.
- ^ a b c Huang Y, Kendall T, Forsythe ES, Dorantes-Acosta A, Li S, Caballero-Pérez J, et al. (2015). “Ancient Origin and Recent Innovations of RNA Polymerase IV and V”. Molecular Biology and Evolution. 32 (7): 1788–1799. doi:10.1093/molbev/msv060. PMC 4476159. PMID 25767205.