Sulfur metabolism-dependent retrograde signaling 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 signaling in the context of plant sulfur metabolism, with a 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 signaling. 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 signaling 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 signaling.