The cell fate controlling CLE40 peptide requires CNGC9 to trigger highly localized Ca2+ transients in Arabidopsis thaliana root meristems

Abstract

Communication between plant cells and their biotic environment is largely dependent on the function of plasma membrane localized receptor-like kinases (RLKs). Major players in this communication within root meristems are secreted peptides, including CLAVATA3/EMBRYO SURROUNDING REGION40 (CLE40). In the distal root meristem, CLE40 acts through the receptor like kinase (RLK) ARABIDOPSIS CRINKLY4 (ACR4) and the leucine-rich repeat (LRR) RLK CLAVATA1 (CLV1) to promote cell differentiation. In the proximal meristem, CLE40 signalling requires the LRR receptor-like protein (RLP) CLAVATA2 (CLV2) and the membrane localized pseudokinase CORYNE (CRN), and serves to inhibit cell differentiation. The molecular components that act immediately downstream of the CLE40-activated receptors are not yet known. Here we show that active CLE40 signalling triggers the release of intracellular Ca2+ leading to increased cytosolic Ca2+ concentration ([Ca2+]cyt) in a subset of proximal root meristem cells. This rise in [Ca2+]cyt depends on the CYCLIC NUCLEOTIDE GATED CHANNEL 9 (CNGC9), CLV1, the CLV1-related BARELY ANY MERISTEM1 (BAM1), CLV2 and CRN. The precise function of changes in [Ca2+]cyt are not yet known, but might form a central part of a fine-tuned response to CLE40 peptide that serves to integrate root meristem growth with stem cell fate decisions and initiation of lateral root primordia.