In some cases, their activity is amplified by post-translational modifications, such as proline hydroxylation and additional arabinosylation 5 6. CLE peptides are encoded endogenously and translated as prepropeptides, which are secreted and processed to yield mature 12–13 amino acid, bioactive peptides 2 3 4. There are ~180 Arabidopsis RKs with extracellular leucine-rich repeat (LRR) domains, many of which can perceive peptide ligands, including members of the CLAVATA3/EMBRYO SURROUNDING REGION (CLE) peptide family 1 2. Receptor kinases (RKs) are key regulators of growth and development in higher plants such as the model organism Arabidopsis thaliana ( Arabidopsis). Our work defines a genetic framework for dissecting CLE peptide signaling and CLV/BAM receptor activation in the root. Moreover, protophloem-specific CRN expression complements resistance of the crn mutant to root-active CLE peptides, suggesting that protophloem is their principal site of action.

CRN stabilizes BAM3 expression and thus is required for BAM3-mediated CLE45 signaling. In contrast to other plant peptide receptors, we found no evidence that SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) proteins act as co-receptor kinases in CLE45 perception.

We uncover BAM3 as the CLE45 receptor in the root and biochemically map its peptide binding surface. Here, we report that the receptor-like protein CLAVATA 2 (CLV2) and the pseudokinase CORYNE (CRN) are necessary to fully sense root-active CLE peptides. How and where different CLE peptides trigger specific morphological or physiological changes in the root is poorly understood. Arabidopsis root development is orchestrated by signaling pathways that consist of different CLAVATA3/EMBRYO SURROUNDING REGION (CLE) peptide ligands and their cognate CLAVATA (CLV) and BARELY ANY MERISTEM (BAM) receptors.

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