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. Here we report how 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 (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 BRIC-17 spaceflight mission. The cultured cell lines were grown within 60 mm 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. Key Words: ARG1-Spaceflight-Gene expression-Physiological adaptation-BRIC. Astrobiology 17, 1077-1111.

Test of Arabidopsis Space Transcriptome: A Discovery Environment to Explore Multiple Plant Biology Spaceflight Experiments

“…For these experiments, Arabidopsis seedlings were grown under a range of growth hardware and lighting conditions. Experiments in the Biological Research in Canisters (BRICs) produced darkgrown samples in cassettes (Petri dish fixation units, PDFUs) that are sealed prior to launch [e.g., (Kwon et al, 2015;Basu et al, 2017;Johnson et al, 2017;Zupanska et al, 2017;Choi et al, 2019)]. Light-grown material was produced in the European Modular Cultivation System [EMCS, with variable RGB lighting and atmospheric and temperature control, e.g., (Correll et al, 2013;Herranz et al, 2019;Vandenbrink et al, 2019)], in SIMBOX [Science in Microgravity Box, LED lighting, e.g., (Fengler et al, 2015)], and in Petri dishes under 24 h LED light in the Veggie hardware [e.g., (Beisel et al, 2019)] or in the Advanced Biological Research System [ABRS, LED lighting; (Paul et al, 2013b)].…”

“…Thus, Zupanska et al (2013) compared Arabidopsis seedlings and wild type cell cultures grown in the dark within the BRIC. Subsequent spaceflight experiments saw comparisons between wild-type Arabidopsis cell cultures and those with mutations in the genes for ALTERED RESPONSE TO GRAVITY 1 (ARG1; a well-studied Arabidopsis gene related to gravity sensing) and HEAT SHOCK FACTOR 2a [HSF2a; a key heat shock response-related transcriptional regulator; (Zupanska et al, 2017;Zupanska et al, 2019)]. Fengler et al (2015) also flew Arabidopsis and rice cell cultures in the SIMBOX hardware on the Shenzhou-8 spacecraft.…”

Root Skewing-Associated Genes Impact the Spaceflight Response of Arabidopsis thaliana

“…Several classes of stress response genes have been identified as consistently involved in the response to spaceflight across ecotypes of Arabidopsis via analyses of gene expression. Heat shock genes are often induced by spaceflight (Paul et al, 2005(Paul et al, , 2012bSalmi and Roux, 2008;Shagimardanova et al, 2010;Zupanska et al, 2013Zupanska et al, , 2017Zupanska et al, , 2019Johnson et al, 2017;Choi et al, 2019). Reactive oxygen species (ROS) signaling and scavenging processes are also common in the spaceflight response, though ROS-associated genes have been observed as both up-and downregulated in spaceflight Abbreviations: d, day; DEG, differentially expressed gene; FLT, spaceflight; GC, ground control; GO, gene ontology; GPI-AP, glycosylphosphatidylinositolanchored protein.…”

“…Mutations in genes associated with stress response and signaling pathways can significantly alter the differential gene expression profiles of spaceflight physiological adaptation. Single gene mutations in heat shock transcription factors, gravity perception genes, and light signaling genes in Arabidopsis seedlings and cultures exhibit altered spaceflight responses Zupanska et al, 2017Zupanska et al, , 2019. Therefore, we sought to understand better the relationships among spaceflight responses, root morphology, and spaceflight adaptation by exploring the spaceflight responses of two single gene skewing-related mutant lines: spiral1 and sku5.…”

Root Tropisms: Investigations on Earth and in Space to Unravel Plant Growth Direction

“…Complicating the investigation of tropisms in a microgravity environment such as the ISS, are the changes in plant growth caused by the absence of gravity, that are not related to gravitropism. These changes have for instance been revealed at the cellular and molecular level in biological systems in which tropisms cannot be defined, such as cultured cells in vitro (Zupanska et al, 2017;Kamal et al, 2018). Apart from changes in fundamental processes such as cell cycle regulation, ribosome biogenesis, and epigenetics, levels of cytokinin were also altered in microgravity (Ferl and Paul, 2016;Kamal et al, 2018).…”