CLAVATA3, a multimeric ligand for the CLAVATA1 receptor-kinase

The CLAVATA1 (CLV1) and CLAVATA3 (CLV3) proteins form a potential receptor and ligand pair that regulates the balance between cell proliferation and differentiation at the shoot meristem of Arabidopsis. CLV1 encodes a receptor-kinase, and CLV3 encodes a predicted small, secreted polypeptide. We demonstrate that the CLV3 and CLV1 proteins coimmunoprecipitate in vivo, that yeast cells expressing CLV1 and CLV2 bind to CLV3 from plant extracts, and that binding requires CLV1 kinase activity. CLV3 only associates with the presumed active CLV1 protein complex in vivo. More than 75% of CLV3 in cauliflower extracts is bound with CLV1, consistent with hypotheses of ligand sequestration. Soluble CLV3 was found in an approximately 25-kilodalton multimeric complex.