The growing story of (ARABIDOPSIS) CRINKLY 4

Abstract

Receptor kinases play important roles in plant growth and development, but only few of them have been functionally characterized in depth. Over the past decade CRINKLY 4 (CR4)-related research has peaked as a result of a newly discovered role of ARABIDOPSIS CR4 (ACR4) in the root. Here, we comprehensively review the available (A)CR4 literature and describe its role in embryo, seed, shoot, and root development, but we also flag an unexpected role in plant defence. In addition, we discuss ACR4 domains and protein structure, describe known ACR4-interacting proteins and substrates, and elaborate on the transcriptional regulation of ACR4 Finally, we address the missing knowledge in our understanding of ACR4 signalling.

Redox-Mediated Endocytosis of a Receptor-Like Kinase during Distal Stem Cell Differentiation Depends on Its Tumor Necrosis Factor Receptor Domain

“…DSC differentiation in the root meristem is strictly regulated by the CLE40-ACR4/CLV1 receptor kinase signaling pathway (Stahl et al, 2009(Stahl et al, , 2013Stahl and Simon, 2012;Czyzewicz et al, 2016). WOX5 is specifically expressed in the QC, where it represses the expression of CYCD3;3 and cell division, thereby maintaining DSCs (Sarkar et al, 2007;Forzani et al, 2014).…”

“…Plasma membrane receptors in plants usually undergo internalization prior to degradation after perceiving ligands, in order to attenuate signaling (Claus et al, 2018;Li, 2018). ACR4 follows the endocytotic pathway for protein internalization and degradation (Gifford et al, 2005;Stahl et al, 2013;Czyzewicz et al, 2016;Claus et al, 2018). ACR4 turnover is substantially accelerated under both negative and positive redox potentials imposed by the exogenous addition of H 2 O 2 or GSH or via endogenously produced redox.…”

“…Our analyses suggest that ACR4 is a key component involved in redox-mediated DSC differentiation. ACR4 becomes internalized and undergoes rapid turnover through the endocytotic pathway (Gifford et al, 2005;Stahl et al, 2013;Czyzewicz et al, 2016). We wanted to know whether the localization of ACR4 is modulated by ROS homeostasis.…”

“…The extracellular domain of ACR4 contains seven crinkly repeats, each with regularly spaced Cys residues, followed by the Cys-rich regions of the TNFR domain (Gifford et al, 2005;Czyzewicz et al, 2016). The kinase and TNFR domains are dispensable for the biological roles of ACR4 in ovule and seed development (Gifford et al, 2005).…”

“…turnover of ACR4-GFP are influenced by redox status, we reasoned that the Cys residues in the extracellular domain of this protein might contribute to its structural stability in a redox environment (Czyzewicz et al, 2016). We investigated the status of the extracellular domain with the transmembrane domain (ET) under treatment with a reductive or oxidative reagent in stably transgenic Pro-35S:ACR4 (ET)-HA-Flag plants (Fig.…”