A bistable circuit involving SCARECROW-RETINOBLASTOMA integrates cues to inform asymmetric stem cell division

Molecular Genetics, Department of Biology, University of Utrecht, 3584 CH Utrecht, The Netherlands.
Cell (Impact Factor: 32.24). 08/2012; 150(5):1002-15. DOI: 10.1016/j.cell.2012.07.017
Source: PubMed


In plants, where cells cannot migrate, asymmetric cell divisions (ACDs) must be confined to the appropriate spatial context. We investigate tissue-generating asymmetric divisions in a stem cell daughter within the Arabidopsis root. Spatial restriction of these divisions requires physical binding of the stem cell regulator SCARECROW (SCR) by the RETINOBLASTOMA-RELATED (RBR) protein. In the stem cell niche, SCR activity is counteracted by phosphorylation of RBR through a cyclinD6;1-CDK complex. This cyclin is itself under transcriptional control of SCR and its partner SHORT ROOT (SHR), creating a robust bistable circuit with either high or low SHR-SCR complex activity. Auxin biases this circuit by promoting CYCD6;1 transcription. Mathematical modeling shows that ACDs are only switched on after integration of radial and longitudinal information, determined by SHR and auxin distribution, respectively. Coupling of cell-cycle progression to protein degradation resets the circuit, resulting in a "flip flop" that constrains asymmetric cell division to the stem cell region.


Available from: Ben Scheres
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    • "Auxin transport has not been described to occur during callus formation. However, callus cells organize in a similar fashion as a root meristem and auxin transport is required for root meristem organization and activity (Grieneisen et al., 2007; Cruz-Ramirez et al., 2012). Thus, it is tempting to speculate if callus organization, might also use auxin transport. "
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