Transcriptinal profile of responses to ER and osmotic stress

Despite the potential of the endoplasmic reticulum (ER) stress response to accommodate adaptive pathways, its integration with other environmental-induced responses is poorly understood in plants. Here, we performed global expression profiling on soybean leaves exposed to polyethylene glycol treatment or to unfolded protein response (UPR) inducers to identify integrated networks between osmotic and ER stress-induced adaptive responses. The results unmasked the major branches of the ER-stress response, which includes enhancing protein folding and degradation in the ER, as well as specific osmotically regulated changes linked to cellular responses induced by dehydration. However, a small proportion (5.5%) of total up-regulated genes represented a shared response that seemed to integrate the two signaling pathways. These co-regulated genes were considered downstream targets based on similar induction kinetics and a synergistic response to the combination of osmotic- and ER-stress-inducing treatments. Genes in this integrated pathway with the strongest synergistic induction encoded proteins with diverse roles. Two of them contained a plant-specific development and cell death (DCD) domain while another had homology to proteins with an ubiquitin-associated (UBA) domain. A NAC domain-containing protein exhibited robust early kinetics of induction consistent with a role as a transfactor. This integrated pathway diverged further from characterized ER-specific branches of UPR as downstream targets were inversely regulated by osmotic stress. Collectively, our results describe a novel branch of the ER stress response that integrates the osmotic signal to potentiate transcription of shared target genes. Keywords: stress response In all experiments two independent biological replicates were used. For each biological replicate, two hybridizations were performed, with dye-swap.