CARK1 mediates ABA signaling by phosphorylation of ABA receptors

Abstract

The function of abscisic acid (ABA) is mediated by its receptors termed RCARs/PYR1/PYLs. Modulation of ABA signaling is vital for plant growth and development. The RCAR-PP2C-SnRK2 regulatory modules have been defined as the core components in ABA signaling. However, it is still not clear whether and how the ABA receptors could be modified at the initial post-translational stage to fine-tune ABA transduction pathway. Here we identify and characterize the putative receptor-like cytoplasmic kinase (RLCK) in Arabidopsis named CARK1, which interacts with RCAR3 (PYL8) and RCAR11 (PYR1) in the manner of phosphorylation. Structural studies of CARK1 revealed the critical active site, N204, which accounts for the kinase activity and the direct interaction with RCAR3/RCAR11. CARK1 phosphorylates RCAR3/RCAR11 at one conserved threonine site, T77/T78. Our genetic analyses further demonstrated that CARK1 positively regulates ABA-mediated physiological responses and overexpression of CARK1 in Arabidopsis distinctly promotes the drought resistance. Moreover, the phosphor-mimic form of RCAR11 in the cark1 mutant is able to functionally complement the ABA sensitivity. CARK1 positively regulates ABA-responsive gene expression and enhances RCAR3/RCAR11’s inhibition to Clade A PP2C. Taken together, our studies strongly support the functional significance of CARK1 in positively regulating ABA signaling via phosphorylation on RCAR3/RCAR11 in Arabidopsis.

Abscisic acid dynamics, signaling, and functions in plants

“…The plasma membrane‐localized leucine‐rich receptor‐like kinase CEPR2 phosphorylates PYLs at a conserved site corresponding to PYL4 Ser54 and promotes degradation of PYLs (Yu et al 2019). A putative receptor‐like cytoplasmic kinase (RLCK) VIII subfamily kinase CARK1 phosphorylates PYR1 and PYL1/2/3/8 at a less conserved site corresponding to PYR1 Thr78 which enhances ABA responses, and the cark1 mutant is less sensitive to ABA (Zhang et al 2018b; Li et al 2019b). CARK1 is activated by ABA, but whether CARK1 be activated by environmental changes or other hormones is still unknown (Zhang et al 2018b).…”

“…A putative receptor‐like cytoplasmic kinase (RLCK) VIII subfamily kinase CARK1 phosphorylates PYR1 and PYL1/2/3/8 at a less conserved site corresponding to PYR1 Thr78 which enhances ABA responses, and the cark1 mutant is less sensitive to ABA (Zhang et al 2018b; Li et al 2019b). CARK1 is activated by ABA, but whether CARK1 be activated by environmental changes or other hormones is still unknown (Zhang et al 2018b). The degradation of PYLs is regulated by both the ubiquitin ligase substrate adaptor DDA1 and RING‐type E3 ligase RSL1 via the ubiquitin‐proteasome system, and by the ESCRT‐I components VPS23A and ALIX through the endosomal‐vacuole pathways (Bueso et al 2014; Irigoyen et al 2014; Yu et al 2016; García‐León et al 2019).…”

Transcriptome Profiling, Biochemical and Physiological Analyses Provide New Insights towards Drought Tolerance in Nicotiana tabacum L.

“…Abscisic acid (ABA) regulates key processes throughout the plant life cycle under both normal and adverse environmental conditions that lead to the expression of genes related to the specific condition by initiating the cell signaling pathways [80]. PYL, PP2C and SnRK2 are the key components of the ABA signaling pathway as PYL are the receptors; PP2C acts as a negative regulator, while SnRK2 acts as a positive regulator in ABA signaling [81]. Our findings showed that all the PYL gene were downregulated in response to drought stress, which are in line with [82].…”

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

“…4c and f) with AMP-PNP from the cocrystal structure of Cytosolic Aba Receptor Kinase 1 (CARK1) ( Fig. 4d and g) [50]. It is possible to observe in the image superimposition ( Fig.…”