Perception of root‐active CLE peptides requires CORYNE function in the phloem vasculature

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.

CLE25 peptide regulates phloem initiation in Arabidopsis through a CLERK‐CLV2 receptor complex

“…In this study, our cellular and biochemical studies show that CLERK and CLV2 interact with each other, providing support for a model in which CLERK and CLV2 function in a complex to perceive the CLE25 peptide. This is in agreement with previous findings that mutations in either CLERK or CLV2 lead to reduced sensitivity to at least l3 CLE peptides, in vitro (Hazak et al 2017; Anne et al 2018). The fact that the CLERK‐CLV2 complex is not able to discriminate these peptides, in these in vitro assays, indicates the potential redundancy among different peptides.…”

“…To analyze whether CLERK and CLV2 function in the known BRX and OPS signal pathways, assays were performed on double mutants of the related genes. These tests established that clv2–101 , but not clerk‐5 , could partially rescue the short‐root phenotype of brx‐2 (Figure C), as recently reported (Hazak et al 2017; Anne et al 2018). However, both clv2–101 and clerk‐5 were able to partially rescue the ops‐1 phenotype (Figure D).…”

“…In phloem development, in vitro treatment using a class of CLE peptides led to short‐root phenotypes, and perturbed protophloem development. The perception of these root‐active peptides requires CLE‐RESISTANT RECEPTOR KINASE (CLERK) (also called CLAVATA3 INSENSITIVE RECEPTOR KINASE2, CIK2), CLV2 and CORYNE (CRN) (Fiers et al 2005; Stahl et al 2009; Hazak et al 2017; Anne et al 2018). CLE45 as a negative regulator suppresses phloem differentiation through BARELY ANY MERISTEM 3 (BAM3)‐CLV2/CRN‐mediated signaling pathway (Depyte et al 2013; Hazak et al 2017).…”

“…The perception of these root‐active peptides requires CLE‐RESISTANT RECEPTOR KINASE (CLERK) (also called CLAVATA3 INSENSITIVE RECEPTOR KINASE2, CIK2), CLV2 and CORYNE (CRN) (Fiers et al 2005; Stahl et al 2009; Hazak et al 2017; Anne et al 2018). CLE45 as a negative regulator suppresses phloem differentiation through BARELY ANY MERISTEM 3 (BAM3)‐CLV2/CRN‐mediated signaling pathway (Depyte et al 2013; Hazak et al 2017). CLE25 and CLE26 , two closely homologous CLE genes expressed in phloem (Czyzewicz et al 2015; Anne et al 2018), deliver a long‐distance drought signal from root to shoot (Takahashi et al 2018) and regulate lateral root formation (Czyzewicz et al 2015), respectively.…”

Regulation of plant peptide hormones and growth factors by post‐translational modification

“…; Hazak et al . ). The closest homologue of CLV3 is CLE40 that is expressed in the differentiation zone of the root stele and in differentiating columella cells (Hobe et al .…”