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Science Signaling  10 Jun 2008:
Vol. 1, Issue 23, pp. ec215
DOI: 10.1126/scisignal.123ec215

Signaling by the CLE small peptide family member CLAVATA 3 (CLV3) restricts stem cell proliferation in the apical meristem of Arabidopsis. CLV3 signals through the transmembrane receptors CLV1 and CLV2 to repress transcription of wuschel (wus), which encodes a homeodomain transcription factor that promotes stem cell proliferation. Müller et al. have identified a new member of this signaling pathway, CORYNE (CRN). A loss-of-function mutation in crn was isolated from a screen for suppressors of a weak meristem-arrest phenotype induced by clv3 overexpression. crn mutants displayed a set of phenotypes shared with clv1 and clv2 loss-of-function mutants, including meristem enlargement due to overproliferation of stem cells, extra carpels, and an increase in the number of meristem cells expressing clv3 and wus. The phenotype of plants carrying loss-of-function mutations in both crn and clv2 was indistinguishable from that of plants carrying either mutation alone. In contrast, plants carrying both crn and clv1 mutations had an exacerbated phenotype that was more severe than with either mutation alone. These genetic interaction experiments indicated that CRN and CLV2 functioned together, whereas CRN and CLV1 acted in parallel. The authors identified the gene affected in the crn mutant and found that it encoded a membrane-associated Ser-Thr kinase expressed in meristems and young organs but not in fully differentiated tissues. The authors propose a model in which CLV signaling is transduced separately through two receptor complexes, one of CLV1 homodimers and one of CRN-CLV2 heterodimers. Whereas CLV1 has both ligand-binding and kinase domains, CLV2 has only a ligand-binding domain, and CRN has only a kinase domain. Together, CRN and CLV2 could thus create a fully functional transmembrane receptor kinase. Consistent with this hypothesis, the crn allele identified through the screen for suppressors of the clv overexpression phenotype had a point mutation that could potentially disrupt dimerization in the transmembrane domain. Both CLV1 and CLV2/CRN transduced the CLV3 signal to WUS through the phosphatases POLTERGEIST (POL) and POLTERGEIST-LIKE 1 (PLL1). Although CLV3 signaling through CLV1 and CLV2/CRN appears to be equivalent in the apical meristem, it is possible that these receptors might differ in their ability to transduce signals from other CLE peptides or confer tissue- or stage-specificity to signaling.

R. Müller, A. Bleckmann, R. Simon, The receptor kinase CORYNE of Arabidopsis transmits the stem cell-limiting signal CLAVATA3 independently of CLAVATA1. Plant Cell 20, 934-946 (2008). [Abstract] [Full Text]

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