Abstract
Mitogen-activated protein kinases (MAPKs) mediate plant immune responses to pathogenic bacteria. However, less is known about the cell autonomous negative regulatory mechanism controlling basal plant immunity. We report the biological role of Arabidopsis thaliana MAPK phosphatase AP2C1 as a negative regulator of plant basal resistance and defense responses to Pseudomonas syringae. AP2C2, a closely related MAPK phosphatase, also negatively controls plant resistance. Loss of AP2C1 leads to enhanced pathogen-induced MAPK activities, increased callose deposition in response to pathogen-associated molecular patterns or to P. syringae pv. tomato (Pto) DC3000, and enhanced resistance to bacterial infection with Pto. We also reveal the impact of AP2C1 on the global transcriptional reprogramming of transcription factors during Pto infection. Importantly, ap2c1 plants show salicylic acid-independent transcriptional reprogramming of several defense genes and enhanced ethylene production in response to Pto. This study pinpoints the specificity of MAPK regulation by the different MAPK phosphatases AP2C1 and MKP1, which control the same MAPK substrates, nevertheless leading to different downstream events. We suggest that precise and specific control of defined MAPKs by MAPK phosphatases during plant challenge with pathogenic bacteria can strongly influence plant resistance.
Highlights
The ability to grow in an environment full of potentially pathogenic microbes is very important for plant survival
We found that loss of AP2C1 leads to strongly enhanced resistance to pv. tomato (Pto) DC3000 that correlates with enhanced PAMPand Pto-induced Mitogen-activated protein kinases (MAPKs) activities displaying particular kinetics, specific transcriptional reprogramming after Pto inoculation, and enhanced accumulation of ET and callose in infected plant tissues
Our study pinpoint the specificity of MAPK regulation by the MAPK phosphatases AP2C1 and MKP1, which control the same substrate MAPKs, but differentially regulate the amplitude or timing of the kinase activities and related downstream events
Summary
The ability to grow in an environment full of potentially pathogenic microbes is very important for plant survival. Plants recognize pathogen-associated molecular patterns (PAMPs), such as flagellin or elongation factor Tu (EF-Tu), via plasma membrane-localized pattern recognition receptors (PRRs) (Macho and Zipfel, 2014) This recognition rapidly activates a signaling network of mitogen-activated protein kinases (MAPKs) (Meng and Zhang, 2013), which induces a 1170 | Shubchynskyy et al. Ser/Thr protein phosphatases of type 2C (PP2C) target pT in the ‘pTEpY’ loop (Meskiene et al, 2003; Fuchs et al, 2013) These types of phosphatases have been found to control MAPK signaling during plant defense. The alfalfa AP2C1 ortholog MP2C inactivates the MPK6 alfalfa ortholog SIMK by dephosphorylating pT in the ‘pTEpY’ motif (Meskiene et al, 2003)
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