Arabidopsis Protein Kinase PKS5 Inhibits the Plasma Membrane H⁺-ATPase by Preventing Interaction with 14-3-3 Protein

Abstract

Regulation of the trans-plasma membrane pH gradient is an important part of plant responses to several hormonal and environmental cues, including auxin, blue light, and fungal elicitors. However, little is known about the signaling components that mediate this regulation. Here, we report that an Arabidopsis thaliana Ser/Thr protein kinase, PKS5, is a negative regulator of the plasma membrane proton pump (PM H+ -ATPase). Loss-of-function pks5 mutant plants are more tolerant of high external pH due to extrusion of protons to the extracellular space. PKS5 phosphorylates the PM H+ -ATPase AHA2 at a novel site, Ser-931, in the C-terminal regulatory domain. Phosphorylation at this site inhibits interaction between the PM H+ -ATPase and an activating 14-3-3 protein in a yeast expression system. We show that PKS5 interacts with the calcium binding protein SCaBP1 and that high external pH can trigger an increase in the concentration of cytosolic-free calcium. These results suggest that PKS5 is part of a calcium-signaling pathway mediating PM H+ -ATPase regulation.

Activation of the plasma membrane Na/H antiporter Salt-Overly-Sensitive 1 (SOS1) by phosphorylation of an auto-inhibitory C-terminal domain

“…PKS5, a SnRK3 kinase similar to SOS2, phosphorylates the H + -ATPase isoform AHA2 at S931 in the C-terminal regulatory domain. Phosphorylation at this site inhibits interaction between the H + -ATPase and an activating 14-3-3 protein binding the neighboring phosphorylated residue T947, thereby preventing the activation of the pump (21). The motif RIDSPSK within the recognition site of SOS2 is also a putative 14-3-3-binding site, but it remains to be determined whether SOS1 interacts with 14-3-3 proteins.…”

“…S2D). Like SOS1, the C terminus of the plasma membrane H + -ATPase includes an autoinhibitory domain to inhibit the activity of the pump (21). PKS5, a SnRK3 kinase similar to SOS2, phosphorylates the H + -ATPase isoform AHA2 at S931 in the C-terminal regulatory domain.…”

Dual Fatty Acyl Modification Determines the Localization and Plasma Membrane Targeting of CBL/CIPK Ca2+ Signaling Complexes in Arabidopsis

“…The resulting CBL/CIPK complexes exert important functions at the plasma membrane by regulating the activity of ion channels and H þ -ATPases (Xu et al, 2006;Fuglsang et al, 2007). The aims of this study were to investigate the potential dual lipid modification of CBL proteins by myristoylation and acylation and to unravel the influence of these lipid modifications on the functional regulation of processes decoding calcium signals.…”

Structural basis of the regulatory mechanism of the plant CIPK family of protein kinases controlling ion homeostasis and abiotic stress

“…Available data suggest a mechanism in which calcium mediates the formation of stable CIPK-CBL complexes that regulate the phosphorylation state and activity of various ion transporters involved in the maintenance of cell ion homeostasis and abiotic stress responses in plants. Among them, the Arabidopsis thaliana CIPK24/SOS2-CBL4/SOS3 complex activates the Na + /H + antiporter SOS1 to maintain intracellular levels of the toxic Na + low under salt stress (7)(8)(9), the CIPK11-CBL2 pair regulates the plasma membrane H + -ATPase AHA2 to control the transmembrane pH gradient (10), the CIPK23-CBL1/9 (11,12) regulates the activity of the K + transporter AKT1 to increase the plant K + uptake capability under limiting K + supply conditions (12,13), and CIPK23-CBL1 mediates nitrate sensing and uptake by phosphorylation of the nitrate transporter CHL1 (14). Together these findings show that understanding the molecular mechanisms underling CIPKs function provides opportunities to increase plant tolerance to abiotic stress and to improve plants for human benefit.…”