Title: Partially Redundant Functions of Arabidopsis DICER-like Enzymes and a Role for DCL4 in Producing trans-Acting siRNAs
Abstract: Arabidopsis encodes four DICER-like (DCL) proteins [1Schauer S.E. Jacobsen S.E. Meinke D.W. Ray A. DICER-LIKE1: Blind men and elephants in Arabidopsis development.Trends Plant Sci. 2002; 7: 487-491Abstract Full Text Full Text PDF PubMed Scopus (375) Google Scholar]. DCL1 produces miRNAs [2Park W. Li J. Song R. Messing J. Chen X. CARPEL FACTORY, a Dicer homolog, and HEN1, a novel protein, act in microRNA metabolism in Arabidopsis thaliana.Curr. Biol. 2002; 12: 1484-1495Abstract Full Text Full Text PDF PubMed Scopus (913) Google Scholar, 3Reinhart B.J. Weinstein E.G. Rhoades M.W. Bartel B. Bartel D.P. MicroRNAs in plants.Genes Dev. 2002; 16: 1616-1626Crossref PubMed Scopus (1582) Google Scholar, 4Kurihara Y. Watanabe Y. Arabidopsis micro-RNA biogenesis through Dicer-like 1 protein functions.Proc. Natl. Acad. Sci. USA. 2004; 101: 12753-12758Crossref PubMed Scopus (711) Google Scholar], DCL2 produces some virus-derived siRNAs, and DCL3 produces endogenous RDR2-dependent siRNAs [5Xie Z. Johansen L.K. Gustafson A.M. Kasschau K.D. Lellis A.D. Zilberman D. Jacobsen S.E. Carrington J.C. Genetic and functional diversification of small RNA pathways in plants.PLoS Biol. 2004; 2: 642-652Crossref Scopus (1119) Google Scholar], but the role of DCL4 is unknown. We show that DCL4 is the primary processor of endogenous RDR6-dependent trans-acting siRNAs (tasiRNAs). Molecular and phenotypic analyses of all dcl double mutants also revealed partially compensatory functions among DCL proteins. In the absence of DCL4, some RDR6-dependent siRNAs were produced by DCL2 and DCL3, and in the absence of DCL3, some RDR2-dependent siRNAs were produced by DCL2 and DCL4. Consistent with partial redundancies, dcl2 and dcl3 mutants developed normally, whereas dcl4 and dcl3 dcl4 mutants had weak and severe rdr6 phenotypes, respectively, and increased tasiRNA target mRNA accumulation. After three generations, dcl3 dcl4 and dcl2 dcl3 mutants exhibited stochastic developmental phenotypes, some of which were lethal, likely owing to the accumulated loss of heterochromatic siRNA-directed marks. dcl1 dcl3 and dcl1 dcl4, but not dcl1 dcl2 mutants, had phenotypes more severe than dcl1 mutants, consistent with DCL1, DCL3, and DCL4 acting as the primary processors of the three respective classes of endogenous silencing RNAs and DCL2 acting to produce viral-derived siRNAs and as an alternative DCL for endogenous siRNA production.