Minisymposium 6: Intercellular Signaling

Abs # 16001: Functional analysis of the CLE gene family in Arabidopsis

Presenter:	Fletcher, Jennifer C, fletcher@nature.berkeley.edu
Authors	Fletcher, Jennifer C (A)   Sharma, Vijay K (A)   Baker, Catherine  (B)   Leasure, Colin D (A)   Meyerowitz, Elliot M (B)
Affiliations:	(A): USDA/UC Berkeley Plant Gene Expression Center (B): California Institute of Technology
Web Site:	http://www.pgec.usda.gov/Fletcher/fletchlab.html

Plants maintain a constant supply of stem cells throughout their life cycle. All the organs of the plant body develop from these pluripotent, self-renewing cells. Mainly there are two places in plants where stem cells are located: the shoot apical meristem (SAM) houses the stem cells for the development of the above-ground parts of the plant, while the root apical meristem produces the underground parts. A number of Arabidopsis thaliana mutants have been isolated that are defective in properly maintaining the stem cell population in the SAM. Plants with mutations at the CLAVATA (CLV)1-3 loci accumulate excess stem cells; conversely, plants with mutations in the WUSCHEL (WUS) gene arrest at very early stages of development because they failure to maintain stem cell identity. The CLV3 and WUS proteins govern the fate of stem cells by a negative feedback loop mechanism. WUS encodes a homeodomain transcription factor, while CLV3 encodes a small secreted polypeptide and CLV1 encodes a leucine-rich repeat receptor kinase (LRR-RLK). There are 216 predicted LRR-RLKs in the Arabidopsis genome, but for only a few is there evidence for ligands and the vast majority of the LRR-RLKs are orphan receptors. We are characterizing a family of CLV3/ESR-related (CLE) genes that have been identified in Arabidopsis and other plants. We have analyzed the expression patterns of 25 Arabidopsis CLE genes by RT-PCR, and have also determined that several encode secreted proteins that could act as potential ligands for other LRR-RLKs. Current experiments combine higher resolution expression analysis by in situ hybridization with functional analysis of loss and gain of function alleles. We have identified loss of function alleles of five CLE genes. Preliminary analyses indicate that, unlike the clv3 mutants, most of these cle mutants do not have dramatic developmental phenotypes, suggesting that they may be redundant and/or play roles in other plant processes. However, over-expression of several other CLE genes under the CaMV 35S promoter is sufficient to perturb SAM and/or flower formation. We have also observed that several CLE genes can, when ectopically expressed, partially compensate for the lack of CLV3 activity. Thus these genes may have partially overlapping functions, or their products may interact with LRR-RLKs that have very similar extracellular ligand binding domains to that of CLV1.