Phosphorylation of Arabidopsis MAP Kinase Phosphatase 1 (MKP1) Is Required for PAMP Responses and Resistance against Bacteria

Abstract

Plants perceive potential pathogens via the recognition of pathogen-associated molecular patterns (PAMPs) by surface-localized pattern recognition receptors, which initiates a series of intracellular responses that ultimately limit bacterial growth. PAMP responses include changes in intracellular protein phosphorylation, including the activation of mitogen-activated protein kinase (MAPK) cascades. MAP kinase phosphatases (MKPs), such as Arabidopsis (Arabidopsis thaliana) MKP1, are important negative regulators of MAPKs and play a crucial role in controlling the intensity and duration of MAPK activation during innate immune signaling. As such, the mkp1 mutant lacking MKP1 displays enhanced PAMP responses and resistance against the virulent bacterium Pseudomonas syringae pv tomato DC3000. Previous in vitro studies showed that MKP1 can be phosphorylated and activated by MPK6, suggesting that phosphorylation may be an important mechanism for regulating MKP1. We found that MKP1 was phosphorylated during PAMP elicitation and that phosphorylation stabilized the protein, resulting in protein accumulation after elicitation. MKP1 also can be stabilized by the proteasome inhibitor MG132, suggesting that MKP1 is constitutively degraded through the proteasome in the resting state. In addition, we investigated the role of MKP1 posttranslational regulation in plant defense by testing whether phenotypes of the mkp1 Arabidopsis mutant could be complemented by expressing phosphorylation site mutations of MKP1. The phosphorylation of MKP1 was found to be required for some, but not all, of MKP1's functions in PAMP responses and defense against bacteria. Together, our results provide insight into the roles of phosphorylation in the regulation of MKP1 during PAMP signaling and resistance to bacteria.

The C-terminal non-catalytic domain of Mkp-1 phosphatase harbors a complex signal for rapid proteasome degradation in enterocytes

“…Previous studies in non-enterocyte cell lines implicated ERK-dependent phosphorylation at the non-catalytic C-terminal domain of Mkp-1 as a modulator of its degradation. As some studies found ERK phosphorylation accelerating 14, 18, 20, 21 , and others delaying Mkp-1 degradation 12, 13, 23, 24, 26, 27 , the role of phosphorylation remains controversial. In the epithelium of rat small intestine, both Mkp-1 and activated ERK localize to crypts (Fig.…”

Post-Translational Modifications of Proteins Have Versatile Roles in Regulating Plant Immune Responses

“…In addition to the PTMs of MAPK cascades mediated by effectors, several phosphatases that negatively regulate these MAPK cascades have been reported. Dual-specificity MAP kinase phosphatases (MKPs), such as MKP1 and MKP2, dephosphorylate both conserved Thr and Tyr residues of the MAPK activation loop, leading to the full inactivation of the MAPKs [95,96,97]. Furthermore, it is suggested that an efficient negative feedback loop exists between MKPs and MAPKs during PAMP responses and bacterial resistance [96].…”

Central Roles and Regulatory Mechanisms of Dual-Specificity MAPK Phosphatases in Developmental and Stress Signaling

“…Interestingly, different expression patterns of wheat TMKP1 were observed between different wheat cultivars with induced expression in sensitive cultivars and repressed in tolerant ones (Zaïdi et al, 2010 ). In contrast, the expression of Arabidopsis MKP1 does not appear to be significantly altered after exposure to either UV-B treatment or pathogen infection (González Besteiro and Ulm, 2013 ; Jiang et al, 2017a ), suggesting that MKP1 is mainly under post-translational regulation. Although the regulation of the IBR5 's transcription has not been reported, it has been shown that IBR5 is post-transcriptionally regulated, generating two transcripts, AT2G004550.1 and AT2G04550.3 , by alternative splicing to produce two IBR5 isoforms IBR5.1 and IBR5.3 (Jayaweera et al, 2014 ).…”

“…For instance, the phosphatase activity of tobacco NtMKP1 is also increased by co-incubation of its substrates such as SIPK (Katou et al, 2005 ), and the catalytic activity of wheat TMKP1 is significantly enhanced by co-incubation of TMPK3 (Zaïdi et al, 2010 ). In addition to in vitro studies, in vivo studies using Arabidopsis transgenic lines expressing MKP1 protein have also shown that MKP1 is phosphorylated in response to both UV-B treatment and pathogen challenges (González Besteiro and Ulm, 2013 ; Jiang et al, 2017a ). The phosphorylation of MKP1 contributes to its stability and is required for its biological function during both UV-B stresses and pathogen infection (González Besteiro and Ulm, 2013 ; Jiang et al, 2017a ).…”

“…In addition to in vitro studies, in vivo studies using Arabidopsis transgenic lines expressing MKP1 protein have also shown that MKP1 is phosphorylated in response to both UV-B treatment and pathogen challenges (González Besteiro and Ulm, 2013 ; Jiang et al, 2017a ). The phosphorylation of MKP1 contributes to its stability and is required for its biological function during both UV-B stresses and pathogen infection (González Besteiro and Ulm, 2013 ; Jiang et al, 2017a ).…”