The CLAVATA3/ESR motif of CLAVATA3 is functionally independent from the nonconserved flanking sequences

It is believed that CLAVATA3 ( CLV3) encodes a peptide ligand that interacts with the CLV1/CLV2 receptor complex to limit the number of stem cells in the shoot apical meristem of Arabidopsis thaliana; however, the exact composition of the functional CLV3 product remains a mystery. A recent study on CLV3 shows that the CLV3/ESR (CLE) motif, together with the adjacent C-terminal sequence, is sufficient to execute CLV3 function when fused behind an N-terminal sequence of ERECTA. Here we show that most of the sequences flanking the CLE motif of CLV3 can be deleted without affecting CLV3 function. Using a liquid culture assay, we demonstrate that CLV3p, a synthetic peptide corresponding to the CLE motif of CLV3, is able to restrict the size of the shoot apical meristem in clv3 seedlings but not in clv1 seedlings. In accordance with this decrease in meristem size, application of CLV3p to in vitro-grown clv3 seedlings restricts the expression of the stem cell-promoting transcription factor WUSCHEL. Thus, we propose that the CLE motif is the functional region of CLV3 and that this region acts independently of its adjacent sequences.