Plant Stem Cell Signaling Involves Ligand-Dependent Trafficking of the CLAVATA1 Receptor Kinase

Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA.
Current biology: CB (Impact Factor: 9.57). 02/2011; 21(5):345-52. DOI: 10.1016/j.cub.2011.01.039
Source: PubMed


Cell numbers in above-ground meristems of plants are thought to be maintained by a feedback loop driven by perception of the glycopeptide ligand CLAVATA3 (CLV3) by the CLAVATA1 (CLV1) receptor kinase and the CLV2/CORYNE (CRN) receptor-like complex. CLV3 produced in the stem cells at the meristem apex limits the expression level of the stem cell-promoting homeodomain protein WUSCHEL (WUS) in the cells beneath, where CLV1 and WUS RNA are localized. WUS downregulation nonautonomously reduces stem cell proliferation. Overexpression of CLV3 eliminates the stem cells, causing meristem termination, and loss of CLV3 function allows meristem overproliferation. There are many questions regarding the CLV3/CLV1 interaction, including where in the meristem it occurs, how it is regulated, and how it is that a large range of CLV3 concentrations gives no meristem size phenotype.
Here we use genetics and live imaging to examine the cell biology of CLV1 in Arabidopsis meristematic tissue. We demonstrate that plasma membrane-localized CLV1 is reduced in concentration by CLV3, which causes trafficking of CLV1 to lytic vacuoles. We find that changes in CLV2 activity have no detectable effects on CLV1 levels. We also find that CLV3 appears to diffuse broadly in meristems, contrary to a recent sequestration model.
This study provides a new model for CLV1 function in plant stem cell maintenance and suggests that downregulation of plasma membrane-localized CLV1 by its CLV3 ligand can account for the buffering of CLV3 signaling in the maintenance of stem cell pools in plants.

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Available from: Paul T Tarr, Jul 08, 2014
    • "Shoot meristem tissue was kept in the feedback loop of CLV-WUS to come true. WUS positively regulates CLV3 expression in overlying cells of the CZ through a non-cell autonomous mechanism, whereas CLV3 is expressed in stem cells of the CZ and delimits the stem cell domain by repressing WUS by binding to CLV1 or CRN/CLV2 receptor-like kinases.[1213] CLV2 which lacks the kinase domain has shown to contribute to the stability of CLV1. "
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    • "Attenuation of signalling has also been suggested to play a role in CLAVATA 3 (CLV3) responses in the maintenance of stem cells. CLV3 triggers vacuolar trafficking of its cognate receptor CLAVATA 1 (CLV1), thereby reducing the plasma membrane levels of the LRR-RLK (Nimchuk et al. 2011). In addition to these LRR-RLKs, trafficking to the recycling and late endosomal pathway was also reported for PRRs as discussed below as well as Arabidopsis CRINKLY 4 (ACR4) and the S-locus RECEPTOR KINASE 3 ( SRK3), respectively , which are both non - LRR - type RLKs ( Tian et al. 2007 ; Ivanov and Gaude 2009 ) . "
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    • "LRR receptor-like kinase, CLAVATA1 (CLV1), which plays crucial roles in the maintenance of the shoot apical meristem, is transported from the plasma membrane to the vacuole upon binding a small peptide hormone, CLV3, in a VTI11-dependent manner (Nimchuk et al. 2011). This vacuolar traffic is required for CLV3-dependent degradation of CLV1 to attenuate CLV signaling. "
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