Activation of active oxygen-generating enzymes to support plant survival — Tokyo University of Science clarifies mechanism using liverwort

Graduate Students Takafumi Hashimoto and Hiroki Shindo of the Graduate School of Science and Technology, Assistant Professor Kenji Hashimoto, Postdoctoral Researcher Dr. Shoko Tsuboyama, and Professor Kazuyuki Kuchitsu of the Faculty of Science and technology of Tokyo University of Science, in collaboration with Associate Professor Takuya Miyakawa of the Graduate School of Biostudies at Kyoto University and Professor Emeritus Masaru Tanokura of the Graduate School of Agricultural and Life Sciences at the University of Tokyo, announced that they have clarified the activation mechanism of a reactive oxygen species (ROS)-generating enzyme (RBOH: Respiratory burst oxidase homolog) in the liverwort plant. The achievement was published in the international academic journal Physiologia Plantarum on December 12, 2023.

ROS, which include superoxide anion radicals and hydrogen peroxide, are a group of highly reactive molecules related to the redox states between oxygen molecules and water. Previously, these molecules were thought to be harmful byproducts generated during animal respiration and plant photosynthesis. However, it has become clear that many eukaryotes, especially plants, have developed enzyme systems that actively produce ROS and utilize them in various biological processes, including immune responses.

In this study, the research group used liverwort as a model plant to investigate the mechanism of ROS generation during the defense response to infection induced by microbial chitin. As a result, chitin was found to induce an increase in the intracellular calcium ion (Ca²⁺) concentration. Furthermore, RBOH is activated upon Ca²⁺ binding, and this binding is enhanced by the phosphorylation of two amino acid residues in the activation-controlling region that is widely conserved among land plants.

The researchers found that the phosphorylation of these two amino acid residues facilitates Ca²⁺ binding to activate RBOH. This activation mechanism may be common to all land plants and is expected to provide important basic knowledge for the future control of various plant functions (e.g., immunity to pathogens, growth, and reproduction) through ROS.

Kuchitsu said, "It is the fate of creatures that breathe oxygen to generate active oxygen (highly reactive and toxic) in the body, and it is also a well-known cause of human diseases and so is sometimes called the devil's substance. However, it has become increasingly clear that active oxygen actually acts as a double-edged sword, possessing both angel and devil aspects. I have been researching various significant aspects of plants actively producing active oxygen. If this mechanism goes out of control, it will produce toxic substances. I presume a strict control mechanism is present to produce only the required amount of active oxygen. In the present study, I clarified the basic control mechanism. In the future, using both the above results as a basis, as well as various engineering techniques, I will also take on the challenge of developing technology for regulating plant growth and environmental adaptability by properly controlling active oxygen."

Journal Information
Publication: Physiologia Plantarum
Title: Enhanced Ca²⁺ binding to EF-hands through phosphorylation of conserved serine residues activates MpRBOHB and chitin-triggered ROS production
DOI: 10.1111/ppl.14101