The CLAVATA1 receptor-like kinase requires CLAVATA3 for its assembly into a signaling complex that includes KAPP and a Rho-related protein

The CLAVATA1 (CLV1) and CLAVATA3 (CLV3) genes are required to maintain the balance between cell proliferation and organ formation at the Arabidopsis s hoot and flower meristems. CLV1 encodes a receptor-like protein kinase. We have found that CLV1 is present in two protein complexes in vivo. One is si milar to 185 kD, and the other is similar to 450 kD. In each complex, CLV1 is part of a disulfide-linked multimer of similar to 185 kD. The 450-kD com plex contains the protein phosphatase KAPP, which is a negative regulator o f CLV1 signaling, and a Rho GTPase-related protein. In clv1 and clv3 mutant s, CLV1 is found primarily in the 185-kD complex. We propose that CLV1 is p resent as an inactive disulfide-linked heterodimer and that CLV3 functions to promote the assembly of the active 450-kD complex, which then relays sig nal transduction through a Rho GTPase.