Cold and salt stress responses are mediated by GCN2 through reactive oxygen species emanating from the chloroplast.

Philip Wayne Morgan
Ansul Lokdarshi, University of Tennessee, Knoxville
Albrecht G. vonArnim, University of Tennessee, Knoxville

Abstract

Cytosolic mRNA translation is subject to global and mRNA-specific control mechanisms in order to balance overall energy and metabolic resources with demand. Phosphorylation of eukaryotic translation initiation factor eIF2a is central to an immediate and reversible switch that represses translation globally. The GCN2 kinase (General Control Non-derepressible-2), is the only known kinase for eIF2a in plants. It can be activated by herbicides that inhibit amino acid biosynthesis. In the study presented here, we provide preliminary evidence of a novel signaling mechanism in Arabidopsis thaliana, where the GCN2-eIF2a paradigm may extend the narrow definition of retrograde signaling by the chloroplast from transcriptional effects in the nucleus to translational regulation in the cytosol. Specifically, conditions that generate reactive oxygen species (ROS) in the chloroplast, such as cold, salt and the herbicide paraquat all rapidly activated the GCN2 kinase. Furthermore, eIF2a phosphorylation was mitigated by photosynthetic inhibitors. Although the global translation profile of gcn2 mutants resembles that of wild type under stress conditions, gcn2 mutants were more sensitive to both cold and salt stress as compared to wild-type in a root elongation assay. This supports the notion that the GCN2-eIF2a pathway is important for ROS signaling during the acclimation to such environmental stressors.

 

Cold and salt stress responses are mediated by GCN2 through reactive oxygen species emanating from the chloroplast.

Cytosolic mRNA translation is subject to global and mRNA-specific control mechanisms in order to balance overall energy and metabolic resources with demand. Phosphorylation of eukaryotic translation initiation factor eIF2a is central to an immediate and reversible switch that represses translation globally. The GCN2 kinase (General Control Non-derepressible-2), is the only known kinase for eIF2a in plants. It can be activated by herbicides that inhibit amino acid biosynthesis. In the study presented here, we provide preliminary evidence of a novel signaling mechanism in Arabidopsis thaliana, where the GCN2-eIF2a paradigm may extend the narrow definition of retrograde signaling by the chloroplast from transcriptional effects in the nucleus to translational regulation in the cytosol. Specifically, conditions that generate reactive oxygen species (ROS) in the chloroplast, such as cold, salt and the herbicide paraquat all rapidly activated the GCN2 kinase. Furthermore, eIF2a phosphorylation was mitigated by photosynthetic inhibitors. Although the global translation profile of gcn2 mutants resembles that of wild type under stress conditions, gcn2 mutants were more sensitive to both cold and salt stress as compared to wild-type in a root elongation assay. This supports the notion that the GCN2-eIF2a pathway is important for ROS signaling during the acclimation to such environmental stressors.