WUSCHEL controls meristem function by direct regulation of cytokinin-inducible response regulators

Abstract

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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Figure 1: Expression profiles of ARR5, ARR6, ARR7 and ARR15.
Figure 2: Expression patterns of ARR7 and WUS in response to meristematic signals.
Figure 3: Direct interaction of WUS with regulatory sequences of ARR7.
Figure 4: Phenotypes of type-A ARR mutant plants.

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Acknowledgements

We thank A. Greenland for providing the AlcA system, J. Palatnik for sharing unpublished results, R. Schwab for establishing the in situ protocol, R. Chen for preparing the WUS antiserum, K. Harter and D. Weigel for discussion, and K. Bomblies, I.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.

Author information

Correspondence to Jan U. Lohmann.

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Competing interests

Microarray data have been deposited at ArrayExpress (http://www.ebi.ac.uk/arrayexpress/) under accession number E-MEXP-432. Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Supplementary information

Supplementary Figure 1

Expression patterns of ARR7 RNA. (PDF 105 kb)

Supplementary Figure 2

Activity of ARR5, ARR6, ARR7 and ARR15 GUS reporter genes. (PDF 65 kb)

Supplementary Figure 3

Direct interaction of WUS with regulatory sequences of ARR7. (PDF 81 kb)

Supplementary Table 1

Genes responsive to WUS induction. (PDF 57 kb)

Supplementary Table 2

Oligonucleotides used in Leibfried et al. (PDF 60 kb)

Supplementary Methods

Additional information on mutants and ChIP. (PDF 68 kb)

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