Reevaluation of the CLV 3‐receptor interaction in the shoot apical meristem: dissection of the CLV 3 signaling pathway from a direct ligand‐binding point of view

Summary The CLAVATA signaling pathway is a key component of the network that controls stem cell renewal and differentiation in Arabidopsis thaliana . CLAVATA 3 ( CLV 3) is a post‐translationally arabinosylated secreted peptide signal that regulates WUSHEL (WUS) transcription to affect the balance of stem cell differentiation and proliferation in the shoot apical meristem ( SAM ). Known membrane‐localized receptors involved in the perception of CLV 3 signaling include CLV 1, the CLV 2/ CORYNE (CRN) complex and RPK 2. The CLV 3 peptide can directly bind to CLV 1; however, it is unclear whether the CLV 3 peptide directly binds to CLV 2 or RPK 2. In this study, we re‐evaluated the direct interaction between CLV 3 and its receptors by photoaffinity labeling with photoactivatable arabinosylated CLV 3. We showed that CLV 2 and RPK 2 exhibited no direct binding to the CLV 3 peptide. Further analysis showed that the receptor kinase BAM 1 directly binds the CLV 3 peptide. A loss‐of‐function clv1 bam1 double mutant exhibited a large number of stem cells that accumulated in the SAM and was insensitive to exogenous treatment with the arabinosylated CLV 3 peptide. WUS gene transcripts were up‐regulated, and the region of WUS expression was enlarged at the SAM in the clv1 bam1 double mutant. These results indicate that CLV 1 and BAM 1 are direct receptors that are sufficient to affect the regulatory network controlling stem cell number in the SAM . In contrast, the CLV 2/ CRN complex and RPK 2 are not involved in direct ligand interactions but may act as co‐receptors.