The role of radical burst via MAPK signaling in plant immunity

Abstract

Plants rely on the innate immune system to defend themselves from pathogen attacks. Reactive oxygen species (ROS) and nitric oxide (NO) play key roles in the activation of disease resistance mechanisms in plants. The evolutionarily conserved mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules in eukaryotes and have been implicated in the plant innate immunity. There have been many disputations about the relationship between the radicals (ROS and NO) and MAPK cascades. Recently, we found that MAPK cascades participate in the regulation of the radical burst. Here, we discuss the regulatory mechanisms of the oxidative and NO bursts in response to pathogen attacks, and crosstalk between MAPK signaling and the radical burst.

Keywords: MAPK; NADPH oxidase; NO burst; oxidative burst; plant immunity.

Figure 1

Proposed radical burst signaling pathways via MAPK cascades. After pathogen recognition, plants immediately provoke Ca²⁺ influxes into cytoplasm, activation of MAPK SIPK and NTF6, and oxidative and NO bursts. SIPK and NTF6 activate the RBOHs expression (regulation at the transcriptional level). The increase in Ca²⁺ concentration in the cytoplasm results in the activation of CDPKs that induce the oxidative burst by direct phosphorylation of RBOHs (regulation at the post-translational level). SIPK also regulates NO burst via unidentified NOS, NOA1 and NR. ROS and NO activate SIPK. Gray arrows indicate positive feedback regulation. The question mark indicates unidentified MAPKKK(s).