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Arg1 functions in the physiological adaptation of undifferentiated plant cells to spaceflight

ABSTRACT: Scientific access to spaceflight and especially the International Space Station has revealed that physiological adaptation to spaceflight is accompanied or enabled by changes in gene expression that significantly alter the transcriptome of cells in spaceflight. A wide range of experiments have shown that plant physiological adaptation to spaceflight involves gene expression changes that alter cell wall and other metabolisms. However, while transcriptome profiling aptly illuminates changes in gene expression that accompany spaceflight adaptation, mutation analysis is required to illuminate key elements required for that adaptation. In this study transcriptome profiling was used to gain insight into the spaceflight adaptation role of Altered response to gravity-1 (Arg1), a gene known to affect gravity responses in plants on Earth. The study compared expression profiles of cultured lines of Arabidopsis thaliana derived from wild type (WT) cultivar Col-0 to profiles from a knock-out line deficient in the gene encoding (ARG1 KO), both on the ground and in space. The cell lines were launched on SpaceX CRS-2 as part of the Cellular Expression Logic (CEL) experiment of the BRIC17 spaceflight mission. The cultured cell lines were grown within 60mm Petri plates in Petri Dish Fixation Units (PDFUs) that were housed within the Biological Research In Canisters (BRIC) hardware. Spaceflight samples were fixed on orbit. Differentially expressed genes were identified between the two environments (spaceflight and comparable ground controls) and the two genotypes (WT and ARG1 KO). Each genotype engaged unique genes during physiological adaptation to the spaceflight environment, with little overlap. Most of the genes altered in expression in spaceflight in WT cells were found to be Arg1-dependent, suggesting a major role for that gene in the physiological adaptation of undifferentiated cells to spaceflight.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE81442 | GEO | 2017/09/01

SECONDARY ACCESSION(S): PRJNA321540

REPOSITORIES: GEO

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Project description:The Heat Shock Factor A2 (HsfA2), as a part of the HSF network, is essential to the plant’s response to almost any environmental stress and to the cellular homeostatic control mechanisms. Plant cell cultures disabled in HsfA2 function were grown aboard the International Space Station (ISS) in order to ascertain whether or not they use the same terrestrially effective systems to adapt to the novel environment of spaceflight. Cultured lines of Arabidopsis thaliana derived from wild type (WT) cultivar Col-0 and from a knock-out line deficient in the gene encoding HSFA2 (HSFA2 KO) were launched to the ISS on SpaceX-2 as part of the Cellular Expression Logic (CEL) experiment of the BRIC17 spaceflight mission and were fixed in-flight after 10 days on orbit. Microarray gene expression data were analyzed using a two-part comparative approach. First, differentially expressed genes were identified between the environments (spaceflight to ground) within cells of the same genotype, which represented physiological adaptation to the spaceflight environment. Second, gene expression profiles were identified between the genotypes (HSFA2 KO to WT) within the same environment, defining genes uniquely required by the two genotypes in the ground and spaceflight adapted states. The physiological state of the cells as a result of disabling a gene has tremendous control over the mechanisms induced to adapt to the environment of spaceflight. The HsfA2 demonstrated a role in the physiological adaptation to the spaceflight environment since the cells disabled in the HsfA2 gene used substantially different genes to achieve the spaceflight adapted state than the WT cells. The endoplasmic reticulum (ER) stress and unfolded protein response (UPR) define the HSFA2 KO cells’ physiological state regardless of the environment and likely result from the deficiency in the chaperone-mediated protein folding machinery. HsfA2 seems to have a universal stress response role but also specific roles in the physiological adaptation to spaceflight through cell wall remodeling, signal perception and transduction and starch biosynthesis. Implementation of knock-out cells identified a set of genes with a required expression level in order for a cell to achieve a spaceflight-adapted state. The HSFA2 KO cells helped to unravel the HsfA2-dependent genes of the adaption of wild type cells to the environment of spaceflight.

Project description:Experimentation on the International Space Station has reached the stage where repeated and nuanced transcriptome studies are beginning to illuminate the structural and metabolic differences between plants grown in space compared to plants on the Earth. Genes that are important in setting up the spaceflight responses are being identified; their role in spaceflight physiological adaptation are increasingly understood, and the fact that different genotypes adapt differently is recognized. However, the basic question of whether these spaceflight responses are required for survival has yet to be posed, and the fundamental notion that spaceflight responses may be non-adaptive has yet to be explored. Therefore the experiments presented here were designed to ask if portions of the plant spaceflight response can be genetically removed without causing loss of spaceflight survival and without causing increased stress responses. The CARA experiment compared the spaceflight transcriptome responses of two Arabidopsis ecotypes, Col-0 and WS, as well as that of a PhyD mutant of Col-0. When grown with the ambient light of the ISS, phyD displayed a significantly reduced spaceflight transcriptome response compared to Col-0, suggesting that altering the activity of a single gene can actually improve spaceflight adaptation by reducing the transcriptome cost of physiological adaptation. The WS genotype showed and even simpler spaceflight transcriptome response in the ambient light of the ISS, more broadly indicating that the plant genotype can be manipulated to reduce the transcriptome cost of plant physiological adaptation to spaceflight and suggesting that genetic manipulation might further reduce, or perhaps eliminate the metabolic cost of spaceflight adaptation. When plants were germinated and then left in the dark on the ISS, the WS genotype actually mounted a larger transcriptome response than Col-0, suggesting that the in-space light environment affects physiological adaptation, which further implies that manipulating the local habitat can also substantially impact the metabolic cost of spaceflight adaptation.

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Arg1 functions in the physiological adaptation of undifferentiated plant cells to spaceflight

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