Transgenic Arabidopsis Gene Expression System - Intracellular Signaling Architecture (APEX-03-2 TAGES-Isa) - 11.21.17

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
On Earth, plants use gravity, moisture and light to determine which way to grow, but the microgravity environment of space causes them to develop different growth habits. The Transgenic Arabidopsis Gene Expression System - Intracellular Signaling Architecture (APEX-03-2 TAGES-Isa) investigation studies thale cress (Arabidopsis thaliana) seedlings grown in microgravity, examining the molecular changes that affect their growth. Results provide new insight into how plants respond to extraterrestrial environments, which improves the research for growing food and producing oxygen on future space missions.
Science Results for Everyone
Scientists are getting to the root of plant growth in space. Auxin is a plant growth hormone that helps guide the direction of root growth. Two experiments on the International Space Station found normal distribution of auxin in the roots of space-grown plants, suggesting weightlessness does not affect this system. However, space-grown plants show differences in root-tip distribution of cytokinin, a plant hormone that often works in concert with auxin to regulate cell division and tissue growth. The effect of weightlessness on distribution of cytokinin in roots suggests that some of the spaceflight-induced features of root growth may be cytokinin-related. Spaceflight also causes changes in the expression of many genes that are regulated by auxin and other plant hormones, as well as genes that regulate the size and shapes of cells that influence root growth patterns. These results provided cell-specific visual markers of where spaceflight-related auxin and cytokinin signaling occur, and how these signals may help to guide root growth in an environment without gravity.

The following content was provided by Robert J. Ferl, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: APEX-03

Principal Investigator(s)
Robert J. Ferl, Ph.D., University of Florida, Gainesville, FL, United States

Anna-Lisa Paul, Ph.D., University of Florida, Gainesville, FL, United States

NASA Kennedy Space Center, Cape Canaveral, FL, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)

Research Benefits
Scientific Discovery, Space Exploration

ISS Expedition Duration
September 2014 - March 2015

Expeditions Assigned

Previous Missions
TAGES-ISA builds upon the previously flown Plant Growth Investigations in Microgravity (PGIM) experiment which flew on STS-93, the Biological Research in Canisters (BRIC)-16 experiment which flew on STS-131, and the Transgenic Arabidopsis Gene Expression System (TAGES) experiment which flew in ABRS during Increments 19-24.

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Experiment Description

Research Overview

  • Plants experiencing spaceflight are quite normal in appearance but can exhibit growth habits distinctly different from plants on earth. This research explores the molecular biology guiding the altered growth of plants in spaceflight.
  • TAGES-Isa specifically addresses the growth and molecular changes that occur in Arabidopsis thaliana plants during spaceflight. By using molecular and genetic tools, fundamental questions regarding root structure, growth and cell wall remodeling may be answered.
  • This investigation advances the fundamental understanding of the molecular biological responses to extraterrestrial environments. This understanding helps to further define the impacts of spaceflight on biological systems to better enable NASA’s future space exploration goals. 

Plants experiencing spaceflight are quite normal in appearance, but can exhibit growth habits distinctly different from plants on earth. Historically, the spaceflight-induced differences were difficult to dissect due to changing hardware and flight conditions. With the ABRS and a consistent ISS orbital environment, it is now possible to confidently approach a dissection of the molecular biology guiding the altered growth of plants in spaceflight. TAGES-ISA involves experiments that specifically address growth and molecular changes in Arabidopsis that occur during spaceflight, bringing the molecular and genetic tools of Arabidopsis to bear on fundamental questions of root morphology, growth, and cell wall remodeling. During the APEX-TAGES experiments, a remarkable number of gene expression changes during spaceflight were observed that are associated with cell wall restructuring, especially in roots. It was also observed, with the ABRS/Green Fluorescent Protein (GFP) imaging system, genetically dependent changes in root growth direction, movement, and structure. The current experiments employ the ABRS and the GFP Imager to dissect, and better understand the molecular changes guiding growth restructuring on orbit. In particular it is hypothesized that spaceflight conditions engender a constant state of root cell wall modification during the cell file rotations that characterize spaceflight-induced root skewing. The specific experiments involve mutants in root growth and cell wall signaling pathways identified in previous spaceflight molecular studies, as well as new GFP biosensor lines also based on the genes identified in the previous flight experiments.

The overall goal of the program is to understand fundamental molecular biological responses to extraterrestrial environments. This goal aligns with fundamental space biology goals to understand the impact of spaceflight on biological systems to better enable the exploration imperative. The research team has used molecular biology and genetically tagged plants as biological monitors of spaceflight and space-related environments with great science return, leading to the development of new biological and hardware tools to study the spaceflight response with even higher fidelity in a wider variety of spaceflight-related environments. The focus of the current proposal is to build on these data and other insights gained from the execution of the APEX-TAGES experiments in the ABRS/GFP Imager, advancing science while also advancing the telemetric imaging hardware and biological experiment support for the ISS and future platforms. Gaining insight into such mechanisms is recognized as fundamental within the decadal study and underpin answers to some of the biggest questions in spaceflight plant biology.

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Space Applications
Plants grown in space are different from those grown on Earth, yet these differences have been hard to study, because each spaceflight is different and experimental hardware continually changes. Previous investigations by the TAGES-ISA team pioneered methods to harvest and preserve plant specimens in space, and the investigation builds on previous plant growth experiments, providing a stronger comparison for plant biologists. Results from this investigation improve scientists’ understanding of the cellular and molecular changes taking place in plants grown in space. This provides fundamental insight for future missions, including efforts to grow food for journeys beyond low-Earth orbit.

Earth Applications
Understanding how plants change in response to their environments provides fundamental insight into plant biology. Results from this investigation have implications for improving agricultural and biomass production, benefiting people on Earth.

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Operational Requirements and Protocols

The time between launch and Run 1 installation into ABRS GFP Imager is 5-12 days. The experiment run duration is 10-12 days. The previous run harvest and next run installation should be scheduled on the same day. The time between harvest and MELFI insertion is 24 hours. Downlink of GFP images is required daily. Harvest photos are required; live video of harvest operations is requested when possible. Only the Water Refill Kit and KFTs return to Earth. KFTs return at -20°C in Cold Bag.

ABRS is prepared for the TAGES-ISA experiment by filling the ABRS water reservoir and installing the ABRS Air Filter Cartridge. To start Run 1 of the TAGES-Isa experiment, six petri plates are removed from a Nomex bag and transferred to the ABRS GFP Imager. GFP and white light images is downlinked on a daily basis. After an experiment duration of 10-12 days, the GFP Imager is removed from ABRS and transferred to the Maintenance Work Area for the harvest activity. Each petri plate is removed from the GFP Imager, photographed, and harvested. The harvest activity requires the crewmember to use forceps to pull the plants from the agar surface on the petri plate. The plants are placed into a KFT and actuated to deliver the RNALater chemical preservative to the plants. The harvest procedure is completed for each of the six petri plates. Upon completion of the harvest, the petri plates for the next run are inserted into the GFP Imager, and the GFP Imager is transferred back to ABRS. Twenty-four hours following the harvest, the KFTs are transferred to MELFI at -80°C. A total of three harvests are completed. At the conclusion of the final harvest, a desiccant pack is inserted into the GFP Imager, the ABRS water reservoir drained, ABRS is powered down, and the Water Refill Kit and APEX-03 Science Spares Kit are returned at ambient, and the KFTs return at -20°C.

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Decadal Survey Recommendations

Plant and Microbial Biology P2

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Results/More Information

On Earth, plant growth is primarily guided by light and gravity. Indeed, it has long been thought that for many of the growth patterns exhibited by plant roots, gravity was required. Research on the ISS has shown that many of these processes are in fact independent of gravity, but scientists are still learning about how plants “know” how to grow without it. Part of this research is investigating how well-characterized plant hormones that function in cell elongation and division – like auxin and cytokinin – work to guide plants in an environment without gravity to act as a cue for where these hormones should be synthesized or repressed. On Earth, auxin (which promotes cell elongation) plays a major role in guiding roots to maintain growth in the direction of the pull of gravity. When a root is growing perfectly vertical (with the tip “down” on Earth) auxin is distributed uniformly through the central region of the root tip, and cell elongation occurs evenly and the root continues its downward growth. However, if the gravity vector is disrupted, as by turning a vertically gown plant on its side, the distribution of auxin shifts so that cell elongation is promoted on the side of the root facing away from the pull of gravity. Those cells elongate until the tip is again pointing down, and the gradient of auxin is again uniformly vertical. Meanwhile, cytokinin is promoting cell division to keep renewing the cells of the root tip as it grows. This scenario describes what happens to the distribution of auxin when the direction of the gravity stimulus is changed on Earth, but what happens if the gravity stimulus is removed all together? Scientists were able to watch the distribution of auxin and cytokinin in roots grown on the ISS by following the distribution of fluorescent markers in real time, the objective being to determine whether gravity plays a direct role in establishing the auxin-mediated gravity-sensing system in primary roots. The current results are from two independent experiments: CARA (Characterizing Arabidopsis Root Attractions) and APEX-03-2 (Advanced Plant Experiment 03-2), which were each completed at different times aboard the International Space Station (ISS). The fluorescent markers were created by making a “reporter gene” composed of a green glowing gene from a jellyfish linked to either an auxin or cytokinin sensor, and then inserting the reporters into plants. Any cells which were actively using auxin or cytokinin would glow green. Scientists were able to view live the distribution of auxin and cytokinin in growing Arabidopsis thaliana plants on the ISS with the Light Microscopy Module (LMM), a specialized fluorescent microscope on the ISS built specifically to work with samples in microgravity. The images from the plant on orbit were compared with control plants imaged on the ground. In addition, spaceflight-grown plants and their ground controls were preserved and also examined post flight. Results showed that space grown plants displayed the normal ground “vertical” distribution of auxin in the primary root. These data suggest that the establishment of the auxin-gradient system, the primary guide for gravity signaling in the root, is not affected by weightlessness, but rather that auxin gradients in the primary root are fundamentally developmental, and those developmental auxin gradients were then coopted to be sensitive to gravity responses. However, the cytokinin distribution in the root tip differs between spaceflight and the ground controls, suggesting spaceflight-induced features of root growth may be cytokinin related. Thus, spaceflight appears benign to auxin and its role in the development of the primary root tip, whereas spaceflight may influence cytokinin-associated processes. The role of auxin in structures other than the root tip bears investigation, as auxin-regulated genes are seen to change in expression during spaceflight, when examining the root as a whole, and root appearance is also influenced by spaceflight. The value of the present study is in having cell-specific visual markers to identify where in the root potential spaceflight auxin-regulated changes do occur.

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Results Publications

    Ferl RJ, Paul AL.  The effect of spaceflight on the gravity-sensing auxin gradient of roots: GFP reporter gene microscopy on orbit. npj Microgravity. 2016 January 21; 2: 15023. DOI: 10.1038/npjmgrav.2015.23.

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Ground Based Results Publications

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ISS Patents

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Related Publications

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Related Websites

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