Global Plant Stress Signaling: Reactive Oxygen Species at the Cross-Road

Abstract

Current technologies have changed biology into a data-intensive field and significantly increased our understanding of signal transduction pathways in plants. However, global defense signaling networks in plants have not been established yet. Considering the apparent intricate nature of signaling mechanisms in plants (due to their sessile nature), studying the points at which different signaling pathways converge, rather than the branches, represents a good start to unravel global plant signaling networks. In this regard, growing evidence shows that the generation of reactive oxygen species (ROS) is one of the most common plant responses to different stresses, representing a point at which various signaling pathways come together. In this review, the complex nature of plant stress signaling networks will be discussed. An emphasis on different signaling players with a specific attention to ROS as the primary source of the signaling battery in plants will be presented. The interactions between ROS and other signaling components, e.g., calcium, redox homeostasis, membranes, G-proteins, MAPKs, plant hormones, and transcription factors will be assessed. A better understanding of the vital roles ROS are playing in plant signaling would help innovate new strategies to improve plant productivity under the circumstances of the increasing severity of environmental conditions and the high demand of food and energy worldwide.

Keywords: abiotic stress; biotic stress; oxidative stress; plant defense; plant stress signaling; reactive oxygen species.

FIGURE 1

A model illustrating how different stresses or stimuli could activate overlapping receptors/sensors but produce distinct final outputs which are specific to each stimulus. In the model, stress A activates different receptors, e.g., 1, 2, 3, 4 and 5, while stress B is perceived by receptors 2, 3, 4, 5, and 6. Receptor 1 is activated only by stress A, while receptor 6 is activated only by stress B. The other receptors are shared between both stimuli representing the cross-talk between stress A and B. With stress A, the interaction between the downstream signaling events led by the receptor combination of 1, 2, 3, 4, and 5 produce a final output which can be completely different from the outcome of the receptor combination of 2, 3, 4, 5, and 6 with stress B.

FIGURE 2

Examples of aspects that have to be taken into consideration while studying signaling networks.

FIGURE 3

Schematic presentation showing that ROS are versatile signaling molecules during plant response to different stresses.

FIGURE 4

Hydroxyl radical (OH^∙) as an example for ROS.

FIGURE 5

A scheme explaining how ROS function at the cross-road of various key signaling events. ROS work upstream and downstream of the other signaling components, e.g., membranes, NADPH oxidases, G-proteins, calcium, redox homeostasis, photosynthesis, MAPKs, plant hormones [such as salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), and ethylene] and transcription factors. Solid arrows for direct ROS interactions with other signaling components, dashed arrows for expected indirect interactions.