Intertwined Roles of Reactive Oxygen Species and Salicylic Acid Signaling Are Crucial for the Plant Response to Biotic Stress

Abstract

One of the earliest hallmarks of plant immune response is production of reactive oxygen species (ROS) in different subcellular compartments, which regulate plant immunity. A suitable equilibrium, which is crucial to prevent ROS overaccumulation leading to oxidative stress, is maintained by salicylic acid (SA), a chief regulator of ROS. However, ROS not only act downstream of SA signaling, but are also proposed to be a central component of a self-amplifying loop that regulates SA signaling as well as the interaction balance between different phytohormones. The exact role of this crosstalk, the position where SA interferes with ROS signaling and ROS interferes with SA signaling and the outcome of this regulation, depend on the origin of ROS but also on the pathosystem. The precise spatiotemporal regulation of organelle-specific ROS and SA levels determine the effectiveness of pathogen arrest and is therefore crucial for a successful immune response. However, the regulatory interplay behind still remains poorly understood, as up until now, the role of organelle-specific ROS and SA in hypersensitive response (HR)-conferred resistance has mostly been studied by altering the level of a single component. In order to address these aspects, a sophisticated combination of research methods for monitoring the spatiotemporal dynamics of key players and transcriptional activity in plants is needed and will most probably consist of biosensors and precision transcriptomics.

Integration of Electrical Signals and Phytohormones in the Control of Systemic Response

“…The SA regulates the expression of various protective genes, primarily those responsible for the redox balance [169][170][171], which occurs not only upon pathogen attacks, but also probably during local heat and light stimuli [33,170,172].…”

Salicylic Acid in Plant Symbioses: Beyond Plant Pathogen Interactions

“…These R proteins, which are generally located within the plant cell, may directly or indirectly recognize their related pathogen- encoded effectors activating ETI [ 1 , 2 ]. Both PTI and ETI are associated with the activation of defenses in the infected tissue, including the generation of reactive oxygen species (ROS) [ 3 ], increase in intracellular Ca 2+ concentrations, and activation of mitogen-activated protein kinases (MAPKs), to finally activate the expression of various defense-associated genes, synthesis of antimicrobial compounds, and accumulation of SA [ 4 , 5 , 6 ].…”

Decoding early stress signaling waves in living plants using nanosensor multiplexing

“…On the other hand, it has been reported that during defense responses against pathogens, increase in SA levels are preceded by apoplastic H 2 O 2 bursts 12 . Recent studies suggest that during plant response to biotic stress, the position where SA interacts with ROS signaling and ROS with SA signaling depends on the pathosystem and the origin of ROS 109 . In our study using pak choi plants, the multiplexed sensors reveal that both high heat and high light stimuli resulted in production of SA but at an earlier time point than the infection-triggered SA generation in pak choi.…”