The Pepper Mitogen-Activated Protein Kinase CaMAPK7 Acts as a Positive Regulator in Response to Ralstonia solanacearum Infection.

Lanping Shi,Zhiqin Liu,Kan Zhang,Baixue Xie,Linjing Xie,Mingxing Yang,Shuilin He

doi:10.3389/fmicb.2021.664926

Lanping Shi, Zhiqin Liu + Show 5 more

Open Access

https://doi.org/10.3389/fmicb.2021.664926

Copy DOI

Abstract

Mitogen-activated protein kinase (MAPK) pathways play a vital role in multiple plant processes, including growth, development, and stress signaling, but their involvement in response to Ralstonia solanacearum is poorly understood, particularly in pepper plants. Herein, CaMAPK7 was identified from the pepper genome and functionally analyzed. The accumulations of CaMAPK7 transcripts and promoter activities were both significantly induced in response to R. solanacearum strain FJC100301 infection, and exogenously applied phytohormones, including methyl jasmonate (MeJA), brassinolide (BR), salicylic acid (SA), and ethephon (ETN), were decreased by abscisic acid (ABA) treatment. Virus-induced gene silencing (VIGS) of CaMAPK7 significantly enhanced the susceptibility of pepper plants to infection by R. solanacearum and downregulated the defense-related marker genes, including CaDEF1, CaPO2, CaSAR82A, and CaWRKY40. In contrast, the ectopic overexpression of CaMAPK7 in transgenic tobacco enhanced resistance to R. solanacearum and upregulated the defense-associated marker genes, including NtHSR201, NtHSR203, NtPR4, PR1a/c, NtPR1b, NtCAT1, and NtACC. Furthermore, transient overexpression of CaMAPK7 in pepper leaves triggered intensive hypersensitive response (HR)-like cell death, H2O2 accumulation, and enriched CaWRKY40 at the promoters of its target genes and drove their transcript accumulations, including CaDEF1, CaPO2, and CaSAR82A. Taken together, these data indicate that R. solanacearum infection induced the expression of CaMAPK7, which indirectly modifies the binding of CaWRKY40 to its downstream targets, including CaDEF1, CaPO2, and CaSAR82A, ultimately leading to the activation of pepper immunity against R. solanacearum. The protein that responds to CaMAPK7 in pepper plants should be isolated in the future to build a signaling bridge between CaMAPK7 and CaWRKY40.

Highlights

As sessile organisms, plants are frequently subjected to unfavorable environmental challenges, including biotic and abiotic stresses, and have to adapt their metabolism, growth, and development (Berriri et al, 2012)
The most extensively studied plant Mitogen-activated protein kinase (MAPK) are Arabidopsis AtMPK6, AtMPK3, and AtMPK4, all of which are activated by several stimuli, including biotic and abiotic stresses (Ichimura et al, 2000; Droillard et al, 2002; Pitzschke et al, 2009; Schikora et al, 2011; Dutilleul et al, 2012)
We found CaMAPK7 transcripts to be induced by inoculation with R. solanacearum

Summary

Introduction

Plants are frequently subjected to unfavorable environmental challenges, including biotic and abiotic stresses, and have to adapt their metabolism, growth, and development (Berriri et al, 2012). The recognition of PAMPs by membrane-targeted pattern recognition receptors (PRRs) in plants triggers an array of signaling pathways, such as calcium flux, the production of reactive oxygen species (ROS), and the activation of mitogenactivated protein kinases (MAPKs). These early events in turn activate the expression of downstream target proteins, such as transcription factors, and eventually lead to the activation of defense-related genes, cell wall strengthening, the biosynthesis of camalexin and other phytoalexins, hypersensitive response (HR)-like cell death mediated by ROS, and induced resistance against pathogens (Zhang and Zhou, 2010; Jiang et al, 2017; Kawasaki et al, 2017; Luo et al, 2017). ETI is often accompanied by the accumulation of phytohormones, such as salicylic acid (SA) and a local HRlike cell death

Methods

Results

Conclusion