Plant Leucine-Rich Repeat Receptor Kinase (LRR-RK): Structure, Ligand Perception, and Activation Mechanism

Abstract

In recent years, secreted peptides have been recognized as essential mediators of intercellular communication which governs plant growth, development, environmental interactions, and other mediated biological responses, such as stem cell homeostasis, cell proliferation, wound healing, hormone sensation, immune defense, and symbiosis, among others. Many of the known secreted peptide ligand receptors belong to the leucine-rich repeat receptor kinase (LRR-RK) family of membrane integral receptors, which contain more than 200 members within Arabidopsis making it the largest family of plant receptor kinases (RKs). Genetic and biochemical studies have provided valuable data regarding peptide ligands and LRR-RKs, however, visualization of ligand/LRR-RK complex structures at the atomic level is vital to understand the functions of LRR-RKs and their mediated biological processes. The structures of many plant LRR-RK receptors in complex with corresponding ligands have been solved by X-ray crystallography, revealing new mechanisms of ligand-induced receptor kinase activation. In this review, we briefly elaborate the peptide ligands, and aim to detail the structures and mechanisms of LRR-RK activation as induced by secreted peptide ligands within plants.

Protein kinases in plant responses to drought, salt, and cold stress

“…Exploring the biological functions of these RLKs is paramount to our understanding of stress signaling and is drawing increasing interest from researchers (Becraft, 2002; De Smet et al, 2009; Chakraborty et al, 2019; Dievart et al, 2020; Wang et al, 2020d). A recent study indicates that the CLAVATA3/EMBRYO‐SURROUNDING REGION‐RELATED 25 (CLE25) peptide can be transported from root vascular tissues to leaves when roots sense decreasing water availability in the soil (Takahashi et al, 2018).…”

Leucine‐rich repeat receptor‐like kinase II phylogenetics reveals five main clades throughout the plant kingdom

“…De Smet et al, 2009). Receptor-like kinases (RLKs), for which the structural basis of ligand perception and signal activation was reviewed by Hohmann et al (2017) and Chakraborty et al (2019), represent the largest group of cell surface receptors in plants, and as such are considered the largest plant gene family, with more than 600 members and representing about 2.5% of protein-coding genes in Arabidopsis (Shiu and Bleecker, 2001;Torii, 2004;Aan den Toorn et al, 2015). Based on Arabidopsis thaliana kinase sequence comparisons using neighbour joining (Shiu and Bleecker, 2001) RLKs were found to be monophyletic, and appear to form one of the clades in the kinase superfamily.…”

Extension of the taxonomic coverage of the family GH126 outside Firmicutes and in silico characterization of its non-catalytic terminal domains

“…3 c) present in various receptor Ser/Thr-protein kinases from Arabidopsis thaliana , such as GSO1 (Okuda et al 2020 ), FLG22 (Sun et al 2013 ) and PEPR1 (Tang et al 2015 ), which are used to sense peptide hormones with diverse sequences at the cell surface. They belong to the LRR receptor kinase family of membrane integral receptors counting in Arabidopsis more than 200 members (Chakraborty et al 2019 ). A typical LRR was originally recognized as a structural motif consisting of repetitive regions of 20–30 amino acid residues rich in leucine, the tandem repeats being connected together forming a solenoid shape (Kobe and Deisenhofer 1994 ; Enkhbayar et al 2003 ).…”

“…Although the analysed N-terminal extension of the family GH126 protein from L. brevis seems to be long enough to adapt an active LRR fold (Fig. 3 c), the fact that its template LRR motifs are present in various members of plant LRR receptor kinase family (Chakraborty et al 2019 ) currently precludes to make a more conclusive prediction concerning its exact function. Finally, concerning the N-terminal extensions of the GH126 proteins from the remaining three lactobacilli (Table 2 ), approximately 100-residue long segment from those extensions could contain the N-terminal part of the homologue of LRR motif present in various virulence factors called internalins from Listeria monocytogenes (Ooi et al 2006 ; Bublitz et al 2008 ; Neves et al 2013 ).…”