All aerobic organisms produce the molecule hydrogen peroxide (H2O2). When present in low concentrations, it acts as a crucial secondary signal to control a variety of biological processes, including but not limited to plant-microbe interactions, abiotic stress tolerance, pollen tube growth, root hair formation, leaf cell expansion, and Casparian strip formation. When present in high concentrations, it causes oxidative stress.
It is yet unknown how plants perceive endogenous H2O2 to control biological processes since the quantities of endogenous H2O2 are too low to effectively oxidize most target proteins.
An illustration of a redox relay with peroxiredoxin B (PRXIIB) serving as a sensor for H2O2 and abscisic acid insensitive 2 (ABI2) serving as a target protein that mediated reactive oxygen species (ROS) signaling during plant immunity was recently published in Nature Plants by a research team led by Prof. Jianmin Zhou from the Institute of Genetics and Developmental Biology (IGDB) of the Chinese Academy of Sciences.
The synthesis of H2O2 is a distinguishing feature of the plant immune system and is essential to plant immunity, including stomatal closure to prevent pathogen invasion.
The study team used mass spectrometry-based analysis called SulfenQ to investigate the processes by which H2O2 modulates plant stomatal immunity. SulfenQ revealed that type II PRXIIB was directly oxidized by H2O2 generated upon immune activation at its peroxidatic cysteine.
Additionally, they demonstrated how PRXIIB and ABI2 can form disulfide conjugates, which can then transmit H2O2 signal to ABI2. This oxidation is necessary for stomatal immunity in plants and significantly increases sensitivity to H2O2-mediated suppression of the ABI2 phosphatase activity.
This study exemplifies the link between endogenous H2O2 sensing and biological processes, and the mechanisms it outlines could be used as a model for future studies on how plants adapt to and grow under stress.
Bi, G., et al. (2022). The cytosolic thiol peroxidase PRXIIB is an intracellular sensor for H2O2 that regulates plant immunity through a redox relay. Nature Plants. doi.org/10.1038/s41477-022-01252-5