Abstract
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. How and where different CLE peptides trigger specific morphological or physiological changes in the root is poorly understood. 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. We uncover BAM3 as the CLE45 receptor in the root and biochemically map its peptide binding surface. 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. CRN stabilizes BAM3 expression and thus is required for BAM3‐mediated CLE45 signaling. 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. Our work defines a genetic framework for dissecting CLE peptide signaling and CLV/BAM receptor activation in the root.
Highlights
Receptor kinases (RKs) are key regulators of growth and development in higher plants such as the model organism Arabidopsis thaliana (Arabidopsis)
Root protophloem differentiation of bam3 loss-offunction mutants is not impaired by exogenously applied CLE45 levels that suppress this process in wild-type plants, suggesting that BARELY ANY MERISTEM 3 (BAM3) could act as a CLE45 receptor [9]
Many of the currently known leucine-rich repeat (LRR)-RKs require shape-complementary coreceptor kinases for receptor activation [46]
Summary
Receptor kinases (RKs) are key regulators of growth and development in higher plants such as the model organism Arabidopsis thaliana (Arabidopsis). 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] In some cases, their activity is amplified by post-translational modifications, such as proline hydroxylation and additional arabinosylation [5,6]. Arabidopsis contains 32 CLE genes, some of which encode redundant peptides, thereby giving rise to 27 distinct CLE peptides [3,7,8] Several of these peptides have been shown to play roles in root development, and chemically synthesized versions of many of them suppress Arabidopsis root growth in tissue culture when applied at nM to low lM concentrations (called root-active CLEs in the following) [9,10,11]. The perception mechanism for most CLE peptides in the root, including their receptors and co-receptors, remains unknown to date
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