Reactive Oxygen Species and Cognate Redox Signaling System in Plant Innate Immunity

Abstract

PAMP elicitor signals trigger a rapid and transient production of reactive oxygen species (ROS) including hydrogen peroxide (H2O2), superoxide (O2 −), singlet oxygen (1O2), and hydroxyl radical (OH˚). The oxidative burst is often a very rapid response induced by elicitor, occurring within seconds to few minutes, suggesting that the process may not require de novo protein synthesis but involves the activation of pre-existing enzymes. Several enzymes including NADPH oxidases, peroxidases, xanthine oxidase, amine oxidases, oxalate oxidase, glycollate oxidase, urate oxidase and lipoxygenase have been implicated in the PAMP-induced ROS production. H2O2 is generated in apoplasts but accumulates to a greater extent in the cytoplasm than in the apoplast. It has been suggested that the apoplastic H2O2 is translocated to cytoplasm for participation in the pathogen defense. ROS plays a central role in launching the defense response against invading pathogens. ROS induces Ca2+ signaling system, reversible phosphorylation, ubiquitin-proteasome signaling pathway, NO signaling system, salicylic acid signaling system, ethylene-mediated signaling system, jasmonic acid signaling system, and abscisic acid-mediated signaling system. The ROS signal functions are manifested as a consequence of their ability to act as mobile carriers of an unpaired electron and are involved in redox signaling system. Redox signaling occurs when at least one step in a signaling event involves one of its components being specifically modified by a reactive oxygen species. Signaling through the redox active molecule H2O2 has been shown to be important in inducing plant defense responses. Expression of several transcription factors has been shown to be regulated by H2O2 and these transcription factors may be direct targets for redox modification by H2O2. ROS signaling system and cognate redox signaling have been shown to be involved in activation of several defense genes. Some pathogens could cause disease mostly by interfering with the H2O2 signaling pathway.