Shared and distinct functions of the pseudokinase CORYNE (CRN) in shoot and root stem cell maintenance of Arabidopsis

Stem cell maintenance in plants depends on the activity of small secreted signaling peptides of the CLAVATA3/EMBRYO SURROUNDING REGION (CLE) family, which, in the shoot, act through at least three kinds of receptor complexes, CLAVATA1 (CLV1) homomers, CLAVATA2 (CLV2) / CORYNE (CRN) heteromers, and CLV1/CLV2/CRN multimers. In the root, the CLV2/CRN receptor complexes function in the proximal meristem to transmit signals from the CLE peptide CLE40. While CLV1 consists of an extracellular receptor domain and an intracellular kinase domain, CLV2, a leucine-rich repeat (LRR) receptor-like protein, and CRN, a protein kinase, have to interact to form a receptor-kinase complex. The kinase domain of CRN has been reported to be catalytically inactive, and it is not yet known how the CLV2/CRN complex can relay the perceived signal into the cells, and whether the kinase domain is necessary for signal transduction at all. In this study we show that the kinase domain of CRN is actively involved in CLV3 signal transduction in the shoot apical meristem of Arabidopsis, but it is dispensable for CRN protein function in root meristem maintenance. Hence, we provide an example of a catalytically inactive pseudokinase that is involved in two homologous pathways, but functions in distinctively different ways in each of them.