Cytokinin stabilizes WUSCHEL by acting on the protein domains required for nuclear enrichment and transcription

PLoS Genet. 2018 Apr 16;14(4):e1007351. doi: 10.1371/journal.pgen.1007351. eCollection 2018 Apr.

Abstract

Concentration-dependent transcriptional regulation and the spatial regulation of transcription factor levels are poorly studied in plant development. WUSCHEL, a stem cell-promoting homeodomain transcription factor, accumulates at a higher level in the rib meristem than in the overlying central zone, which harbors stem cells in the shoot apical meristems of Arabidopsis thaliana. The differential accumulation of WUSCHEL in adjacent cells is critical for the spatial regulation and levels of CLAVATA3, a negative regulator of WUSCHEL transcription. Earlier studies have revealed that DNA-dependent dimerization, subcellular partitioning and protein destabilization control WUSCHEL protein levels and spatial accumulation. Moreover, the destabilization of WUSCHEL may also depend on the protein concentration. However, the roles of extrinsic spatial cues in maintaining differential accumulation of WUS are not understood. Through transient manipulation of hormone levels, hormone response patterns and analysis of the receptor mutants, we show that cytokinin signaling in the rib meristem acts through the transcriptional regulatory domains, the acidic domain and the WUSCHEL-box, to stabilize the WUS protein. Furthermore, we show that the same WUSCHEL-box functions as a degron sequence in cytokinin deficient regions in the central zone, leading to the destabilization of WUSCHEL. The coupled functions of the WUSCHEL-box in nuclear retention as described earlier, together with cytokinin sensing, reinforce higher nuclear accumulation of WUSCHEL in the rib meristem. In contrast a sub-threshold level may expose the WUSCHEL-box to destabilizing signals in the central zone. Thus, the cytokinin signaling acts as an asymmetric spatial cue in stabilizing the WUSCHEL protein to lead to its differential accumulation in neighboring cells, which is critical for concentration-dependent spatial regulation of CLAVATA3 transcription and meristem maintenance. Furthermore, our work shows that cytokinin response is regulated independently of the WUSCHEL function which may provide robustness to the regulation of WUSCHEL concentration.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / cytology
  • Arabidopsis / genetics*
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / chemistry
  • Arabidopsis Proteins / genetics*
  • Arabidopsis Proteins / metabolism*
  • Cell Nucleus / metabolism
  • Cytokinins / metabolism*
  • Gene Expression Regulation, Plant
  • Genes, Plant
  • Homeodomain Proteins / chemistry
  • Homeodomain Proteins / genetics*
  • Homeodomain Proteins / metabolism*
  • Meristem / metabolism
  • Models, Biological
  • Mutation
  • Plant Growth Regulators / metabolism*
  • Plants, Genetically Modified
  • Protein Domains
  • Protein Stability
  • Signal Transduction
  • Stem Cells / metabolism
  • Transcription, Genetic

Substances

  • AT2G27250 protein, Arabidopsis
  • Arabidopsis Proteins
  • Cytokinins
  • Homeodomain Proteins
  • Plant Growth Regulators
  • WUSCHEL protein, Arabidopsis

Grants and funding

This work was supported by National Science Foundation grant (IOS-1456725) to GVR, Agricultural Experiment Station Mission Funding Program, UCR to GVR, and JSPS Postdoctoral Fellowships for Research Abroad to KNM. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.