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

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

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.664926

DOI=10.3389/fmicb.2021.664926

ISSN=1664-302X

ABSTRACT=<p>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 <italic>Ralstonia solanacearum</italic> is poorly understood, particularly in pepper plants. Herein, <italic>CaMAPK7</italic> was identified from the pepper genome and functionally analyzed. The accumulations of <italic>CaMAPK7</italic> transcripts and promoter activities were both significantly induced in response to <italic>R. solanacearum</italic> 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 <italic>CaMAPK7</italic> significantly enhanced the susceptibility of pepper plants to infection by <italic>R. solanacearum</italic> and downregulated the defense-related marker genes, including <italic>CaDEF1</italic>, <italic>CaPO2</italic>, <italic>CaSAR82A</italic>, and <italic>CaWRKY40</italic>. In contrast, the ectopic overexpression of <italic>CaMAPK7</italic> in transgenic tobacco enhanced resistance to <italic>R. solanacearum</italic> and upregulated the defense-associated marker genes, including <italic>NtHSR201</italic>, <italic>NtHSR203</italic>, <italic>NtPR4</italic>, <italic>PR1a/c</italic>, <italic>NtPR1b</italic>, <italic>NtCAT1</italic>, and <italic>NtACC</italic>. Furthermore, transient overexpression of <italic>CaMAPK7</italic> in pepper leaves triggered intensive hypersensitive response (HR)-like cell death, H<sub>2</sub>O<sub>2</sub> accumulation, and enriched CaWRKY40 at the promoters of its target genes and drove their transcript accumulations, including <italic>CaDEF1</italic>, <italic>CaPO2</italic>, and <italic>CaSAR82A</italic>. Taken together, these data indicate that <italic>R. solanacearum</italic> infection induced the expression of <italic>CaMAPK7</italic>, which indirectly modifies the binding of CaWRKY40 to its downstream targets, including <italic>CaDEF1</italic>, <italic>CaPO2</italic>, and <italic>CaSAR82A</italic>, ultimately leading to the activation of pepper immunity against <italic>R. solanacearum</italic>. The protein that responds to CaMAPK7 in pepper plants should be isolated in the future to build a signaling bridge between CaMAPK7 and CaWRKY40.</p>