Arabidopsis thaliana RECEPTOR DEAD KINASE1 Functions as a Positive Regulator in Plant Responses to ABA

Abstract

Abscisic acid (ABA) is a major phytohormone involved in important stress-related and developmental plant processes. Membrane-delimited ABA signal transduction plays an important role in early ABA signaling, but the molecular mechanisms connecting core signaling components to the plasma membrane remain unclear. Plants have evolved a large number of receptor-like kinases (RLKs) to modulate diverse biological processes by perceiving extracellular stimuli and activating downstream signaling responses. In this study, a putative leucine-rich repeat-RLK gene named RECEPTOR DEAD KINASE1 (AtRDK1) was identified and characterized in Arabidopsis thaliana. RDK1 promoter-GUS analysis revealed that RDK1 is expressed ubiquitously in the various tissues in Arabidopsis, and its expression is mainly induced by ABA. In the presence of ABA, RDK1-deficient rdk1-1 and rdk1-2 lines showed significant resistance in cotyledon greening and root growth, whereas RDK1-overexpressing lines showed enhanced sensitivity. Consistently, the expression of ABA-responsive genes was significantly downregulated in rdk1 mutant seedlings, which were also hypersensitive to drought stress with increased water loss. Interestingly, RDK1 was found to be an atypical kinase localized to the plasma membrane and did not require its kinase activity during ABA-mediated inhibition of seedling development. Accordingly, RDK1 interacted in the plasma membrane with type 2C protein phosphatase ABSCISIC ACID INSENSITIVE1 (ABI1); this interaction was further enhanced by exogenous application of ABA, suggesting that RDK1-mediated recruitment of ABI1 onto the plasma membrane is important for ABA signaling. Taken together, these results reveal an important role for RDK1 in plant responses to abiotic stress conditions in an ABA-dependent manner.

Atypical Receptor Kinase RINRK1 Required for Rhizobial Infection But Not Nodule Development in Lotus japonicus

“…These proteins were proposed to have diverged to become signal transduction proteins despite their lack of kinase activity (Castells and Casacuberta, 2007). Typical examples are BIR2, which acts in BAK1-mediated plant immunity (Halter et al, 2014); STRUBBELIG (SUB), which acts in leaf and floral organ development (Chevalier et al, 2005); POLLEN-SPECIFIC RECEPTOR-LIKE KINASE 5 (PRK5), which acts in PAMP associated plant immunity (Wrzaczek et al, 2015); and RDK1, which acts in in abiotic stress signaling (Kumar et al, 2017). The mechanistic basis of signaling via atypical RLKs is not understood, but all these proteins are essential for signal transduction and are proposed to function via protein-protein interactions.…”

“…The mechanistic basis of signaling via atypical RLKs is not understood, but all these proteins are essential for signal transduction and are proposed to function via protein-protein interactions. For example, BIR2 interacts with BAK1 and RDK1 interacts with ABI1 in Arabidopsis (Halter et al, 2014;Kumar et al, 2017). Identification and characterization of proteins that interact with RINRK1 and RINRK2 will be needed to help us understand how these signaling kinase-like proteins promote formation and propagation of infection threads.…”

“…in NFR1, SYMRK, and AtBAK1). Inactive RLKs, such as STRUBBELIG, BAK1-Interacting Receptor-like Kinase 2 (BIR2), and Receptor Dead Kinase 1 (RDK1), also have Asn at this position (Halter et al, 2014;Kumar et al, 2017). Moreover, RINRK1 and RINRK2 have EYG residues instead of the DFG motif of subdomain VII, which is involved in cation binding and orientation of the ATP gamma phosphate for phosphate transfer (Hanks et al, 1988; Fig.…”

Abscisic acid dynamics, signaling, and functions in plants

“…In contrast, under stressed conditions or ABA treatment, activities of PP2Cs can be reduced by ABA receptor PYLs and several other regulators, such as the putative leucine‐rich repeat‐RLK, RECEPTOR DEAD KINASE1 (RDK1) that can promote ABA responses by interacting with ABI1 (Kumar et al 2017). PP2Cs are also degraded by the 26S proteasome pathway through the PUB12/13 U‐box, RGLG1/5 RING‐type and multimeric cullinc3 (CUL3)‐RING‐based E3 ligases by interacting with the adaptor BTB/POZ AND MATH DOMAIN proteins (BPMs), which is promoted by ABA (Figure 2) (Kong et al 2015; Wu et al 2016; Belda‐Palazon et al 2019; Julian et al 2019).…”

Crystal structure of DRIK1, a stress-responsive receptor-like pseudokinase, reveals the molecular basis for the absence of ATP binding

“…Pseudokinases can act as auxiliary proteins perturbing the conformation of the protein partner by allosteric regulation or acting as a scaffold recruiting a catalytically active kinase to trigger protein activation via phosphorylation. For example, the Arabidopsis pseudokinases Bak1-Interacting Receptor-Like Kinase2 (BIR2), Coryne (CRN) and Receptor Dead Kinase 1 mediate immune responses, stem cell homeostasis, and plant responses to ABA during seedling development, respectively [29][30][31][32][33]. Another example is the receptor-like pseudokinase Guard Cell Hydrogen Peroxide-Resistant 1 (GHR1), which acts as a scaffold interacting with Slow Anion Channel 1 (SLAC1) and with Calcium-Dependent Protein Kinase 3 (CPK3) to induce stomatal closure [26].…”