EGR 2 phosphatase regulates OST 1 kinase activity and freezing tolerance in Arabidopsis

Abstract

OST1 (open stomata 1) protein kinase plays a central role in regulating freezing tolerance in Arabidopsis; however, the mechanism underlying cold activation of OST1 remains unknown. Here, we report that a plasma membrane-localized clade-E growth-regulating 2 (EGR2) phosphatase interacts with OST1 and inhibits OST1 activity under normal conditions. EGR2 is N-myristoylated by Nmyristoyltransferase NMT1 at 22°C, which is important for its interaction with OST1. Moreover, myristoylation of EGR2 is required for its function in plant freezing tolerance. Under cold stress, the interaction of EGR2 and NMT1 is attenuated, leading to the suppression of EGR2 myristoylation in plants. Plant newly synthesized unmyristoylated EGR2 has decreased binding ability to OST1 and also interferes with the EGR2-OST1 interaction under cold stress. Consequently, the EGR2-mediated inhibition of OST1 activity is released. Consistently, mutations of EGRs cause plant tolerance to freezing, whereas overexpression of EGR2 exhibits decreased freezing tolerance. This study thus unravels a molecular mechanism underlying cold activation of OST1 by membranelocalized EGR2 and suggests that a myristoyl switch on EGR2 helps plants to adapt to cold stress.

Abscisic acid dynamics, signaling, and functions in plants

“…Besides clade A PP2Cs, EGR1/2/3 suppress plant growth partially through dephosphorylating microtubule‐associated protein MASP1 at Ser670 and destabilizing microtubules which are required for appropriate levels of growth under osmotic stress (Bhaskara et al 2017). They also inhibit proline accumulation and suppress resistance responses to drought and cold stresses through suppressing SnRK2 activation (Bhaskara et al 2017; Ding et al 2019). Ancient PYL without ABA binding affinity has been reported in algae, while PP2Cs and SnRK2s from algae have conserved functions compared with those from higher plants (Lind et al 2015; de Vries et al 2018; Cheng et al 2019; Sun et al 2019).…”

“…The PR5 receptor‐like kinase 2 (PR5K2) may also repress ABA and stress signaling through phosphorylating ABI1/2 and enhancing their protein phosphatase activities (Baek et al 2019). Moreover, function of the clade E PP2C, EGR2 requires myristoylation by NMT1, which is suppressed by cold stress (Ding et al 2019).…”

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

“…Cytoplasmic PP2A dephosphorylates the receptor kinase BRI1 to inhibit BR response, but nuclear PP2A dephosphorylates and stabilizes BZR1 to activate BR response (Wang et al, ). Other examples where localization is likely to determine the substrates available to the phosphatase are Clade E PP2Cs that are localized along the plasma membrane and whose putative targets are predominantly membrane and cytoskeleton proteins (Bhaskara, Wen, Nguyen, & Verslues, ; Ding et al, ). Similarly, it was shown that plasma membrane‐associated Clade D PP2Cs affected cell expansion via regulation of plasma membrane AHA phosphorylation, whereas those localized in cytoplasm or other cellular compartments did not (Ren et al, ).…”

“…Recently reported functional characterization of the EGR PP2Cs and Clade A PP2C HAI1. Top: EGRs (Clade E PP2Cs) were shown to dephosphorylate and inactivate SnRK2.6 (also known as OST1 or SnRK2E; Ding et al, ). EGRs were also found to regulate the phosphorylation status of microtubule‐associated stress protein 1 (MASP1) as well as additional plasma membrane and cytoskeleton associated proteins (Bhaskara, Wen, et al, ).…”

Comparative transcriptomic analysis reveals the relationship between cold-acclimation and vernalization

“…LTI (LOW TEMPERATURE INDUCED) and RAB (RESPONSIVE TO ABSCISIC ACID) participate in freezing tolerance and osmotic stress [28]. Protein kinase OST1 (OPEN STOMATA 1) enhances freezing tolerance by regulating ICE1 phosphorylation [29,30]. BES1 (BRI1-EMS-SUPPRESSOR 1) played an essential role in BR signal transduction, positively regulating CBF expression [31].…”