ROS signaling loops — production, perception, regulation

• ROS production is strictly regulated and integrated with other signaling networks in plants.
• Calcium has a critical role in ROS signaling and the control of ROS production.
• Extracellular ROS production originates from different sources that have non-overlapping roles.
• Intracellular ROS perception is provided by parallel systems of oxidative protein modification and redox status monitoring.
• NPR1 serves as a central intracellular integrator of ROS, nitric oxide and salicylic acid signaling pathways.

Reactive oxygen species are recognized as important signaling components in a wide range of processes in plants and most other organisms. Reactive oxygen species are produced in different subcellular compartments in response to specific stimuli and the production is under tight control in order to avoid detrimental side-effects. Calcium signaling, protein phosphorylation and other signaling pathways are intimately involved in the control and coordination of reactive oxygen production. Any signal that should result in a specific response must eventually be perceived. Direct redox modification of transcription factors and other proteins are critical for the perception of intracellular reactive oxygen species; however, sensing of their extracellular counterparts awaits elucidation.