Title: Regulation of AUXIN RESPONSE FACTOR3 by TAS3 ta-siRNA Affects Developmental Timing and Patterning in Arabidopsis
Abstract: MicroRNAs (miRNAs) and trans-acting siRNAs (ta-siRNAs) in plants form through distinct pathways, although they function as negative regulators of mRNA targets by similar mechanisms [1Allen E. Xie Z. Gustafson A.M. Carrington J.C. microRNA-directed phasing during trans-acting siRNA biogenesis in plants.Cell. 2005; 121: 207-221Abstract Full Text Full Text PDF PubMed Scopus (1627) Google Scholar, 2Gasciolli V. Mallory A.C. Bartel D.P. Vaucheret H. Partially redundant functions of Arabidopsis DICER-like enzymes and a role for DCL4 in producing trans-acting siRNAs.Curr. Biol. 2005; 15: 1494-1500Abstract Full Text Full Text PDF PubMed Scopus (430) Google Scholar, 3Jones-Rhoades M.W. Bartel D.P. Bartel B. MicroRNAs and their regulatory roles in plants.Annu. Rev. Plant Biol. 2006; 57: 19-53Crossref PubMed Scopus (1930) Google Scholar, 4Peragine A. Yoshikawa M. Wu G. Albrecht H.L. Poethig R.S. SGS3 and SGS2/SDE1/RDR6 are required for juvenile development and the production of trans-acting siRNAs in Arabidopsis.Genes Dev. 2004; 18: 2368-2379Crossref PubMed Scopus (668) Google Scholar, 5Vazquez F. Vaucheret H. Rajagopalan R. Lepers C. Gasciolli V. Mallory A.C. Hilbert J.L. Bartel D.P. Crete P. Endogenous trans-acting siRNAs regulate the accumulation of Arabidopsis mRNAs.Mol. Cell. 2004; 16: 69-79Abstract Full Text Full Text PDF PubMed Scopus (599) Google Scholar, 6Xie Z. Allen E. Wilken A. Carrington J.C. DICER-LIKE 4 functions in trans-acting small interfering RNA biogenesis and vegetative phase change in Arabidopsis thaliana.Proc. Natl. Acad. Sci. USA. 2005; 102: 12984-12989Crossref PubMed Scopus (402) Google Scholar, 7Yoshikawa M. Peragine A. Park M.Y. Poethig R.S. A pathway for the biogenesis of trans-acting siRNAs in Arabidopsis.Genes Dev. 2005; 19: 2164-2175Crossref PubMed Scopus (526) Google Scholar]. Three ta-siRNA gene families (TAS1, TAS2, and TAS3) are known in Arabidopsis thaliana. Biogenesis of TAS3 ta-siRNAs, which target mRNAs encoding several AUXIN RESPONSE FACTORs (including ARF3/ETTIN and ARF4 [1Allen E. Xie Z. Gustafson A.M. Carrington J.C. microRNA-directed phasing during trans-acting siRNA biogenesis in plants.Cell. 2005; 121: 207-221Abstract Full Text Full Text PDF PubMed Scopus (1627) Google Scholar, 8Williams L. Carles C.C. Osmont K.S. Fletcher J.C. A database analysis method identifies an endogenous trans-acting short-interfering RNA that targets the Arabidopsis ARF2, ARF3, and ARF4 genes.Proc. Natl. Acad. Sci. USA. 2005; 102: 9703-9708Crossref PubMed Scopus (225) Google Scholar]) involves miR390-guided processing of primary transcripts, conversion of a precursor to dsRNA through RNA-DEPENDENT RNA POLYMERASE6 (RDR6) activity, and sequential DICER-LIKE4 (DCL4)-mediated cleavage events. We show that the juvenile-to-adult phase transition is normally suppressed by TAS3 ta-siRNAs, in an ARGONAUTE7-dependent manner, through negative regulation of ARF3 mRNA. Expression of a nontargeted ARF3 mutant (ARF3mut) in a wild-type background reproduced the phase-change phenotypes detected in rdr6-15 and dcl4-2 mutants, which lose all ta-siRNAs. Expression of either ARF3 or ARF3mut in rdr6-15 plants, in which both endogenous and transgenic copies of ARF3 were derepressed, resulted in further acceleration of phase change and severe morphological and patterning defects of leaves and floral organs. In light of the functions of ARF3 and ARF4 in organ asymmetry, these data reveal multiple roles for TAS3 ta-siRNA-mediated regulation of ARF genes in developmental timing and patterning.