Relevance of Unfolded Protein Response to Spaceflight-Induced Transcriptional Reprogramming in Arabidopsis

Plants are primary producers of food and oxygen on Earth and will likewise be indispensable to the establishment of large-scale sustainable ecosystems and human survival in space. To contribute to the understanding of how plants respond to spaceflight stresses, we examined the relevance of the unfolded protein response (UPR), a conserved signaling cascade that responds to a number of unfavorable environmental stresses, in the model plant species Arabidopsis thaliana. To do so, we compared the transcriptional responses of wild type and UPR-defective seedlings to spaceflight during the SpaceX-CRS12 mission to the International Space Station. We established that orbital culture substantially altered the expression of hundreds of stress related genes compared to ground control conditions. Although many of these genes were differentially regulated in the UPR mutants in the ground control conditions compared to wild type, their expression was largely equalized in all genotypes by flight. Our results have yielded new information on how plants respond to growth in orbit and support the hypothesis that spaceflight induces the activation of signaling pathways that compensate for the loss of UPR regulators in the control of downstream transcriptional regulatory networks.