Sulfur metabolism-dependent retrograde signalling for oxidative stress acclimation

Plant sulfur metabolism is crucial to the plant acclimation response to abiotic stresses, providing the redox-active compounds cysteine and glutathione for redox buffering as well as the chloroplast-to-nucleus retrograde signal 3'-phosphoadenosine 5'-phosphate (PAP) for activation of gene expression changes. Whilst these processes have been conventionally considered separately, here we review chloroplast retrograde signalling in the context of plant sulfur metabolism, with focus on the biosynthesis and degradation of PAP in secondary sulfur metabolism. We outline mechanisms by which primary sulfur metabolism via cysteine and glutathione contribute to the modulation of chloroplast retrograde signalling. We examine emerging questions in how plant sulfur metabolism is coordinated in different cell types of a plant leaf for synthesis and accumulation of PAP. Finally, while the majority of chloroplast retrograde signalling research has focused on the model Brassicaceae plant species Arabidopsis thaliana, here we outline the opportunities for novel insights from non-Brassicaceae plants to enable an integrated understanding of the intersection of sulfur metabolism and retrograde signalling.