Abstract
ABSTRACTCLAVATA3/EMBRYO SURROUNDING REGION (CLE) peptides are secreted endogenous plant ligands that are sensed by receptor kinases (RKs) to convey environmental and developmental inputs. Typically, this involves an RK with narrow ligand specificity that signals together with a more promiscuous co-receptor. For most CLEs, biologically relevant (co-)receptors are unknown. The dimer of the receptor-like protein CLAVATA 2 (CLV2) and the pseudokinase CORYNE (CRN) conditions perception of so-called root-active CLE peptides, the exogenous application of which suppresses root growth by preventing protophloem formation in the meristem. clv2 as well as crn null mutants are resistant to root-active CLE peptides, possibly because CLV2-CRN promotes expression of their cognate receptors. Here, we have identified the CLE-RESISTANT RECEPTOR KINASE (CLERK) gene, which is required for full sensing of root-active CLE peptides in early developing protophloem. CLERK protein can be replaced by its close homologs, SENESCENCE-ASSOCIATED RECEPTOR-LIKE KINASE (SARK) and NSP-INTERACTING KINASE 1 (NIK1). Yet neither CLERK nor NIK1 ectodomains interact biochemically with described CLE receptor ectodomains. Consistently, CLERK also acts genetically independently of CLV2-CRN. We, thus, have discovered a novel hub for redundant CLE sensing in the root.
Highlights
The endogenous CLAVATA3/EMBRYO SURROUNDING REGION (CLE) peptides of plants are secreted as propeptides and processed to yield bioactive 12-14 amino acid long ligands (Cock and McCormick, 2001; Ito et al, 2006; Kondo et al, 2006)
Ten lines that were substantially resistant to a RESULTS Identification of CLE26- and CLE45-responsive genes in the VISUAL assay In an attempt to isolate novel components of CLE peptide signaling in A. thaliana root protophloem development, we embarked on a combinatorial approach of transcriptomic analysis and forward genetics
A T-DNA insertion allele of CLE-RESISTANT RECEPTOR KINASE (CLERK) obtained from the Arabidopsis stock center displayed strong CLE26 resistance (Fig. 1E)
Summary
The endogenous CLAVATA3/EMBRYO SURROUNDING REGION (CLE) peptides of plants are secreted as propeptides and processed to yield bioactive 12-14 amino acid long ligands (Cock and McCormick, 2001; Ito et al, 2006; Kondo et al, 2006). The LRR-RK BARELY ANY MERISTEM 3 (BAM3) is necessary for CLE45-triggered suppression of protophloem sieve element differentiation (Depuydt et al, 2013; Hazak et al, 2017; Kang and Hardtke, 2016). Genetic analyses suggest that CLE45 and its cognate receptor BAM3 (Hazak et al, 2017) oppose the activity of positive regulators of protophloem sieve element differentiation, such as BREVIS RADIX (BRX) or OCTOPUS (OPS) (Depuydt et al, 2013; Rodriguez-Villalon et al, 2014, 2015). Because bam null mutants do not display a root phenotype (Depuydt et al, 2013; RodriguezVillalon et al, 2014, 2015), this might involve redundant pathways, for example signaling by CLE26 (Czyzewicz et al, 2015; Rodriguez-Villalon et al, 2015), the receptor for which is unknown
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