The CLE family of plant polypeptide signaling molecules

Cell. Mol. Life Sci. 65 (2008) 743 755 1420-682X/08/050743-13DOI 10.1007/s00018-007-7411-5 Birkh user Verlag, Basel, 2007

Cellular and Molecular Life Sciences

ReviewThe CLE family of plant polypeptide signaling molecules

J. H. Juna,b,, E. Fiumea,b, and J. C. Fletchera,b,*

a Plant Gene Expression Center, USDA/UC Berkeley, 800 Buchanan Street, Albany, California 94710 (USA)

b Department of Plant and Microbial Biology, University of California, Berkeley, California 94720 (USA), Fax: [phone], e-mail: [email protected]

Received 6 September 2007; received after revision 13 October 2007; accepted 23 October 2007 Online First 24 November 2007

Abstract. Polypeptide ligands have long been recognized as primary signaling molecules in diverse physiological processes in animal systems. Recent studies in plants have provided major breakthroughs with the discovery that small polypeptides are also involved in many plant biological processes, indicating that the use of polypeptides as signaling molecules in cell-to-cell communication is evolutionarily conserved. The CLAVATA3 (CLV3)/ENDOSPERM SURROUNDING REGION (ESR)-related (CLE) proteins are currently the best understood family of

small polypeptides in plants. The recent isolation of MCLV3 from Arabidopsis and TDIF from a Zinnia cell culture system indicates that biologically active CLE polypeptides are produced by post-translational proteolysis and modification, similar to peptide hormone production in animals and yeast. Here, we review exciting discoveries involving the identification of the CLE proteins and their functions in various aspects of plant development, including restriction of stem cell accumulation by CLV3 and inhibition of xylem differentiation by TDIF.

Keywords. Polypeptide ligand, Arabidopsis, signaling, CLAVATA3 (CLV3)/ENDOSPERM SURROUNDING REGION (ESR)-related (CLE), receptor-like kinase, meristem, xylem differentiation.

Introduction

Cells in multicellular organisms must communicate with one another in order to regulate their growth and division and to coordinate their functions. Since the discovery of insulin in 1922 [1] established the fact that polypeptides can be used as signaling molecules in a diverse range of physiological processes, extracellular peptide ligands have been found to be key mediators of cell-to-cell communication in animal systems [2, 3].For example, the transforming growth factor-beta (TGF-b) and epidermal growth factor (EGF) super-families consist of diverse groups of polypeptide growth factors that regulate cell duplication, migra-

tion, differentiation and survival [4, 5]. One feature of these polypeptide signals is that they are produced from larger pre-pro-proteins that undergo proteolytic cleavage of the signal peptide...