Plants continuously maintain pools of totipotent stem cells in their apical meristems from which elaborate root and shoot systems are produced. In Arabidopsis thaliana, stem cell fate in the shoot apical meristem is controlled by a regulatory network that includes the CLAVATA (CLV) ligand–receptor system and the homeodomain protein WUSCHEL (WUS)1,2. Phytohormones such as auxin and cytokinin are also important for meristem regulation3. Here we show a mechanistic link between the CLV/WUS network and hormonal control. WUS, a positive regulator of stem cells, directly represses the transcription of several two-component ARABIDOPSIS RESPONSE REGULATOR genes (ARR5, ARR6, ARR7 and ARR15), which act in the negative-feedback loop of cytokinin signalling4,5. These data indicate that ARR genes might negatively influence meristem size and that their repression by WUS might be necessary for proper meristem function. Consistent with this hypothesis is our observation that a mutant ARR7 allele, which mimics the active, phosphorylated form, causes the formation of aberrant shoot apical meristems. Conversely, a loss-of-function mutation in a maize ARR homologue was recently shown to cause enlarged meristems6.
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We thank A. Greenland for providing the AlcA system, J. Palatnik for sharing unpublished results, R. Schwab for establishing the in situ protocol, R. Chen for preparing the WUS antiserum, K. Harter and D. Weigel for discussion, and K. Bomblies, I. Lohmann, M. Schmid, J. Palatnik and D. Weigel for reading the manuscript critically. This work was supported by a Career Development Award of the International Human Frontier Science Program (HFSP) Organization (J.U.L.), a Ph.D. fellowship of the Cusanuswerk (W.B.), grants from the NSF and the NIH (J.J.K.) and the Max Planck Society (J.U.L).Author Contributions A.L. performed in situ hybridizations and qRT–PCRs, constructed reporter genes, the mutated alleles of ARR7 and performed electron microscopy; J.P.C.T. and J.J.K. generated and analysed the arr double and septuple mutants; W.B. performed the ChIP experiments; S.S. generated constructs and transgenic lines of ARR genes; A.K. generated AlcA::CLV3 plants; M.D. performed qRT–PCRs; and J.U.L. carried out the microarray experiment and analysis, performed gel-shifts and wrote the paper. All authors discussed the results and commented on the manuscript.
Expression patterns of ARR7 RNA. (PDF 105 kb)
Activity of ARR5, ARR6, ARR7 and ARR15 GUS reporter genes. (PDF 65 kb)
Direct interaction of WUS with regulatory sequences of ARR7. (PDF 81 kb)
Genes responsive to WUS induction. (PDF 57 kb)
Oligonucleotides used in Leibfried et al. (PDF 60 kb)
Additional information on mutants and ChIP. (PDF 68 kb)
About this article
Journal of Integrative Plant Biology (2019)
Current Opinion in Plant Biology (2019)
Plant Biotechnology Journal (2019)
Mitogen-activated protein kinases MPK3 and MPK6 are required for stem cell maintenance in the Arabidopsis shoot apical meristem
Plant Cell Reports (2019)
Current Opinion in Plant Biology (2019)