Reactive oxygen species (ROS) are highly reactive molecules containing oxygen. These compounds, that are common byproducts of biological processes in all living things akin to aerobic respiration and photosynthesis, are highly toxic. In most cases, ROS damage the cellular machinery and might trigger a deleterious stress response if their levels should not kept in strict check. This is why antioxidants are such a vital a part of our weight loss program.
However, in the previous couple of many years, scientists have discovered that ROS are sometimes produced in cells intentionally for various purposes. Tokyo University of Science (TUS) professor Kazuki Kachetsu has long been a proponent of the idea that ROS act as a double-edged sword. Over the course of several studies, Prof. Kachitsu and his colleagues have demonstrated that plants contain quite a lot of enzymes that generate ROS under different conditions, akin to when fighting fungal or bacterial infections, during growth, development and reproduction. During. As fertilization, and when adjusting internal or external stress.
In a few of these studies, researchers investigated the mechanisms by which plants activate the ROS-generating enzymes NADPH oxidases (also referred to as RBOHs). They play vital roles not only in plants but in addition in animals including humans and fungi. However, many features of the biological significance of this process remain to be explored. Furthermore, the activity of those enzymes should be tightly regulated in all organisms. The study of the evolution of regulatory mechanisms and the function of RBOHs is a vital topic in various research fields, including medical and pharmaceutical sciences and microbiology.
So far, two activation mechanisms have been identified for RBOHs. One involves the binding of calcium ions (Ca2+) on two small structures called EF-hands. Others require a chemical modification called phosphorylation on specific amino acids. This modification is carried out by protein kinases. However, the precise relationship between these two mechanisms and the way they regulate ROS generation is unclear.
Against this background, a research team led by Prof. Kachetsu and including Mr. Takafumi Hashimoto, Ph.D. Students, Assistant Professor Kenji Hashimoto, Dr. Shuko Tsuboyama, and Mr. Hiroki Shindo, all from TUS, together with Dr. Takuya Miyakawa and Professor Masaru Tanukura set out to deal with this information gap. They previously published a study elucidating the function and regulatory mechanisms of plant RBOHs. Now, of their latest article, published on December 12, 2023 within the journal Physiologia Planetarium, the team revealed the underlying mechanism by which MPRBOHB, the ROS-generating RBOH, is activated. Interestingly, these mechanisms appear to be conserved in RBOHs in all land plants.
Through experiments within the liverwort model Marchantia polymorpha and genetically modified cell lines, the researchers were the primary to exhibit that activation of MPRBOHB requires not only a rise in intracellular Ca.2+ concentration but in addition binding with Ca2+ Ions span roughly 200 amino acids in two regions within the EF hands. In these tests, they used fragments of chitin to stimulate an immune response in cells because chitin is an integral part of the cell partitions of microorganisms akin to molds and fungi.
Then, through detailed examination of specific regions around highly conserved EF-hands in all land plants, the researchers identified two serine amino acid residues that, when phosphorylated, increase Ca.2+ Binding Affiliation of MPRBOHB. “Our results show that the binding of calcium ions acts as a molecular switch that activates MPRBOHB, and that phosphorylation of two specific serine residues plays a role in facilitating this binding,” Professor Kachitsu explains. “We believe that these mechanisms, orchestrated by a conserved regulatory domain, constitute the primary regulatory process controlling all land plant RBOHs.”
Understanding how plants regulate ROS-generating enzymes could have tremendous implications for humanity. The insights gained may result in tools to artificially manipulate ROS production in plants. In turn, this ability may be used to extend crop yields, make plants more resilient to pollutants or invasive microorganisms, and even clean plants of environmental pollutants.
“ROS production plays a very wide range of important functions in plants, including growth, reproduction, immunity, and stress response. Proper control of this production helps us improve agriculture and food quality. together can help in environmental remediation,” highlighted Professor Kochitsu. “It is hoped that this work will help to address a wide range of plant-related social issues, serving as a critical foundation for future research.”