Kumamoto University
[ Graduate School of Science and Technology]

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CLAVATA signal in Arabidopsis

Introduction

Meristem

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The term meristem was first defined by Carl Wilhelm von Na ̈ geli
in his book ‘‘Beitrage zur Wissenschaftlichen Botanik’’. Meristem is a formative plant tissue made up of cells capable of dividing and giving rise to new cells. Because of their essential role in higher plants, meristems have received much attention from plant scientists for more than 150 years. The shoot apical meristem (SAM) and the root apical meristem (RAM) are known to be two important meristems that provide cells for postembryonic growth and development.The SAM produces all aerial parts of postembryonic organs, and the RAM promotes the continuous growth of roots. Even though the structures of the SAM and RAM differ, the signaling components required for stem cell maintenance seem to be relatively conserved.

CLAVATA signal

The plant meristems, shoot apical meristem (SAM) and root apical meristem (RAM), are unique structures made up of a self-renewing population of undifferentiated pluripotent stem cells. Both meristems utilize cell-to-cell communication to maintain proper meristematic activities and meristem organization and to coordinate new organ formation. In SAM, an essential regulatory mechanism for meristem organization is a regulatory loop between WUSCHEL (WUS) and CLAVATA (CLV), which functions in a non-cell-autonomous manner. This intercellular sig- naling network coordinates the development of the organization center, organ boundaries and distant organs. The CLAVATA3/ESR (CLE)-related genes produce signal peptides, which act non-cell-autonomously in the meristem regulation in SAM.
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CLV3 peptide hormone function in a non-cell autonomous manner

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The downstream target of the CLV signaling pathway is the WUS transcription factor in Arabidopsis. WUS gene expression is negatively regulated by CLV signaling and promotes stem cell proliferation in Arabidopsis.

Synthetic peptides are also functional in vivo, and it can be used as a good material to isolate downstream gene mutants which show insensitivity against to synthetic CLV3 peptide.
(Ito et al., Science 2006: Kinoshita et al., Development 2010)






Analyses of CLV3 signaling pathway

Isolation of downstream genes of CLV3

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 In order to identify novel molecular components operating in the CLV3 signalling pathway, we have performed mutational screens for insensitivity to MCLV3 on ~10,000 M2 plants derived from EMS-mutagenised Arabidopsis seed pools. A total of 14 mutants, designated clv3 peptide insensitive (cli) mutants, were isolated for maintaining the SAM when grown on agar media containing 5uM CLV3 peptide. We identified that SOL2/CRN encodes receptor like kinase (Miwa et al., 2008), and CLI1/RPK2 encodes LRR-RLK (Kinoshita et al., 2010).

Peptidase, responsible for CLV3 peptide maturation.

 As is known before, peptidase function in peptide hormone maturation steps. We already identified one peptidase which catalyze CLE pre-protein.

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Next generation sequencer

 We have many peptide resistant mutants. In order to identify the mutation point, next generation sequencer is used. By using it, we can easily identify the causal genes.