A winning two pair: Role of the redox pairs AsA/DHA and GSH/GSSG in signal transduction

Abstract

For a few decades after its identification, the AsA/GSH (Halliwell-Asada) cycle has been almost exclusively considered as a scavenging system, more or less efficiently removing reactive oxygen species (ROS). The whole issue was simplistically viewed as a fight between bad ROS and good antioxidants until recently, when ROS (and reactive nitrogen species, RNS) were identified as important signalling molecules, inducing an array of defensive responses in both animal and plant systems. In this framework, antioxidants take a completely different role, becoming part of complex signalling modules. AsA and GSH are connected in many ways, forming a functional entity. Still they have their own specificity and control different aspects of plant metabolism and growth. It is increasingly clear that AsA and GSH, together with their oxidized forms, have a pivotal, multi-level regulatory role in protein function and gene expression. Remarkable progress has been recently achieved in the identification of transcription factors and other proteins, whose activity is regulated by changes in the relative amount of redox components. Additionally, participation of AsA as a co-substrate of reactions catalysed by dioxygenases (a large class of enzymes involved in hormone synthesis and post-translational protein modification), also has a relevant regulatory role.