Hydrogen peroxide and calcium ion form circuits that amplify plant stress responses
Torres and Berlanga propose in a recent Spotlight article published in Molecular Plant that hydrogen peroxide forms, together with the calcium ion, several loops/circuits that amplify the regulatory signals, allowing the generation of a magnified response to stress situations.
Plants produce hydrogen peroxide (H2O2) not to kill microbes or cells but to act as a signal that activates and amplifies responses to pathogen attack or various environmental stresses. To do this, plant cells have some enzymes in the plasma membrane, NADPH oxidases, which produce this hydrogen peroxide that oxidizes some amino acids of proteins, modifying their activity. Thus, a few minutes after the attack or stress situation, H2O2 is produced, which acts as a signaling molecule and interacts with other plant signals such as calcium ion (Ca2+) or phosphorylation that also modify the activity of regulatory proteins, to generate the appropriate response.
The authors comment on an investigation carried out by Wang
et al., who study the action of abscisic acid (ABA), a plant hormone that promotes, among other responses, resistance to drought and oxidative stress, and where they characterize two protein kinases that phosphorylate and activate the NADPH oxidase to produce H2O2. In the context of recent research in the field, Torres and Berlanga propose various pathways through which H2O2 amplifies the stress response. On the one hand, H2O2 can modify and inhibit negative regulators of the ABA response, such as phosphatases that keep the activating kinases inactivated, thus contributing to increasing the response to this hormone. On the other hand, H2O2 can modify and activate specific receptors that open Ca2+ channels, allowing Ca2+ entry into the cell to activate NADPH oxidases to produce more H2O2. This activation can be direct, by binding Ca2+ directly to the NADPH oxidase, or indirectly, through protein kinases that target this enzyme. The balance is that H2O2 interacts with other regulatory elements of the response to abscisic acid to augment the H2O2 level itself and increase the signaling of this hormone, contributing to improve the response to drought and other stress situations.
Figure 1. Various amplification circuits increase H2O2 production and Ca2+ signaling in response to ABA (from -Torres and Berlanga. 2023. Molecular Plant, 16, 968970 ).