Modulation of ABA responses by the protein kinase WNK8

Abstract

Abscisic acid (ABA) regulates growth and developmental processes in response to limiting water conditions. ABA functions through a core signaling pathway consisting of PYR1/PYL/RCAR ABA receptors, type 2C protein phosphatases (PP2Cs), and SnRK2‐type protein kinases. Other signaling modules might converge with ABA signals through the modulation of core ABA signaling components. We have investigated the role of the protein kinase WNK8 in ABA signaling. WNK8 interacted with PP2CA and PYR1, phosphorylated PYR1 in vitro, and was dephosphorylated by PP2CA. A hypermorphic wnk8‐ct Arabidopsis mutant allele suppressed ABA and glucose hypersensitivities of pp2ca‐1 mutants during young seedling development, and WNK8 expression in protoplasts suppressed ABA‐induced reporter gene expression. We conclude that WNK8 functions as a negative modulator of ABA signaling.

Upstream Open Reading Frame Mediated Translation of WNK8 Is Required for ABA Response in Arabidopsis

“…The expression of the two ABA response genes was also induced in plants transformed with pWNK8m : WNK8 but was lower than their expression in Col-0 and wnk8 mutant plants. This suggested that WNK8 negatively affected the expression of ABA response genes, which is consistent with a previous study [ 28 ].…”

“…A previous study showed that different T-DNA insertion mutants of WNK8 led to opposite ABA responses during seed germination [ 28 ]. To learn more about the roles of WNK8 in response to ABA, two T-DNA insertion mutants, SALK_206987C ( wnk8-1 ) and SALK_103318C ( wnk8-2 ), were used in this study ( Figure 1 A).…”

“…Studies have shown that AtWNK8 expression is enhanced under salt and sorbitol treatments and that the wnk8 mutant lines have higher proline content and exhibit significant catalase (CAT) and peroxidase (POD) activities, which lead to in high salinity and osmotic stress tolerance [ 23 ]. Furthermore, AtWNK8 has been proposed to negatively modulate ABA signaling by interacting with ABA-signaling core components, including the ABA receptor, PYR1, and type 2C protein phosphatase (PP2CA) [ 28 ]. In contrast, AtWNK9 positively regulates ABA signaling and enhances drought tolerance in transgenic plants [ 24 ].…”

The flip side of phospho‐signalling: Regulation of protein dephosphorylation and the protein phosphatase 2Cs

“…PP2C regulation of Ca2+/calmodulin‐dependent protein kinase has been observed in rice (Ni et al, ; Shi et al, ). Interaction of with‐no‐lysine kinase 8 (WNK8) with the Clade A PP2C ABA‐hypersensitive germination 3 (PP2CA/AHG3) reduced WNK8 autophosphorylation activity (Waadt et al, ). Based on the data from other organisms, we can also speculate that other types of kinases are regulated by PP2Cs even though such regulation has not yet been characterized in plants.…”

Distinct Roles of N-Terminal Fatty Acid Acylation of the Salinity-Sensor Protein SOS3

“…To express these SOS3 variants with C-terminal GFP fusions in Nicotiana benthamiana , the corresponding SOS3 cDNAs were transferred to vector pGreen-II with the CaMV35S promoter (John Innes Centre). For co-localization with subcellular markers, the nucleo-cytoplasmic mCherry protein in plasmid pGGZ-YL038 ( Waadt et al, 2019 ), and the mRFP-tagged plasma membrane protein LTI6b (plasmid pUBN-mRFP-LTI6b) were used. To generate pUBN-mRFP-LTI6b, an entry clone encoding LTI6b ( At3g05890 ) was constructed by PCR amplification of the LTI6b coding sequence from PM-YC3.6-Lti6b ( Krebs et al, 2012 ) using primers 5'-AAAAAGCAGGCTGTATGAGTACAGCCAC-3' and 5'-AGAAAGCTGGGTTCACTTGGTGATG-3' that contained attB1 and attB2 sites, respectively.…”