BRIC-19: TOAST II & GeneLAB Experiment, 2014
The Gilroy Lab has been again fortunate to secure NASA funding for a second experiment studying the growth of Arabidopsis plants in microgravity on the International Space Station (ISS). This experiment is called BRIC-19: Test Of Arabidopsis Space Transcriptome II (TOAST II) and GeneLAB. Similar to BRIC-17, we will use the BRIC (Biological Research In Canisters) hardware with our plants growing in petri plates inside PDFU (Petri Dish Fixation Units) as we did for BRIC-17. Our experiment will launch on September 19, 2014, tucked inside SpaceX’s Dragon capsule as part of the CRS-4 (cargo resupply mission #4). The Dragon will berth with the ISS two days later on September 21, 2014, at which point the astronauts will unpack our BRICs into the ISS and our experiment will begin.
So, what exactly will we be investigating during our second foray to the ISS?
The first half of our BRIC-19 experiment is TOAST II. Just as the lack of weight on board the International Space Station causes astronauts to lose bone mass, the weightless environment causes plants to lose their supporting structures. For the plant this means they grow long and thin in space, lacking to some degree the thickened and strengthened cell walls that they use to hold themselves up on Earth. The reason the plants are stronger on Earth is that they sense the mechanical forces generated by their own weight and lay down support materials in response to these signals. In space, the signals are gone and so the plants don’t produce the support materials. As astronaut Don Pettit (who grew the famous Space Zucchini!) put it: Plants “get lazy” in space.
Part of the machinery that lets the plant sense and respond to these mechanical forces on Earth is a group of genes called the “TOUCH” genes, so named because they are switched on in response to touch. One of these genes, named TOUCH 2, or TCH2, looks to be an important hub for a lot of information processing in the plant and so we think that the product of the TCH2 gene, i.e., the TCH2 protein, is a key regulator of the plant’s ability to sense mechanical forces such as its own weight. Dr. Janet Braam’s research group in Rice University has been able to make mutant plants with forms of TCH2 that is either always “on” or always unable to trigger touch responses. Dr. Braam very generously shared these mutants with us and so we now have plants that have this master mechanical response trigger always on or off. The plan is to compare the ‘always on’ and ‘always off ‘ to a normal plant growing in space and see if activating the touch response pathway even in the mechanically “silent” world of spaceflight can help restore growth that is more like what we normally see on Earth. We will look not only at the plants’ growth but also at their transcriptomes (the expression level of every gene in the plant) to see if the growth and gene expression of have the hallmarks of being at 1 x gravity, even in the weightlessness of space.
The other half of our BRIC-19 experiment is called GeneLAB, an exciting new program in NASA where data from experiments on the International Space Station is rapidly released to the entire research community to allow as many people as possible to study the dataset for insight into how spaceflight affects biology. The Gilroy Lab has the honor of sending the first GeneLAB experiment to the ISS!
The idea behind our GeneLAB work is that many plant biologists use the “lab rat” of plant research, Arabidopsis thaliana (also known as Mouse Ear Cress), to perform their experiments in space. This is a small, extremely well studied plant which has an enormous range of tools to help dissect its functions down to the level of genes and chemicals. Arabidopsis grows naturally in many places around the world and although Arabidopsis thaliana from Poland or China is all ‘Arabidopsis’, the plants in each area have diverged a little bit from each other and so there are varieties of Arabidopsis local to each area. These varieties are called ‘ecotypes’ and each is a little different from the next. So the question we want to answer is, do the different ecotypes used by researchers respond differently to spaceflight? If they do, which ecotype you use for your experiment might be critically important! The way to test this possibility would be to grow different ecotypes on the Space Station and compare them to the same ecotypes grown under the same conditions on Earth. Our GeneLAB experiment is to investigate this idea using three commonly used ecotypes of Arabidopsis. The ecotypes are all named after where they were found and collected, so the ones we will use are named Ws (Wassilewskija, collected in Belarus), Cvi (from the Cape Verdi Islands) and Ler (Landsberg erecta, orginally from Poland). In addition we will be using the Columbia ecotype (from Columbia Missouri, USA) in our TOAST II experiment, giving us a 4-way comparison of ecotype responses. As with TOAST II, we will look at the growth of the plants and then look at the patterns of genes that are switched on and off in each ecotype in response to growing in space.
If all goes as planned, we should get our ISS-grown BRIC-19 samples for analysis following the Dragon splashdown when the capsule returns to earth from the ISS in late October, 2014.
BRIC-17: TOAST, 2013
The Gilroy Lab experiment growing plants in microgravity, called BRIC-17, flew via Space X’s Dragon/F9 to the International Space Station (ISS) in March 2013. A number of plant scientists interested in testing their hypotheses in microgravity submitted proposals to the National Aeronautics and Space Administration (NASA) in the spring of 2012, and in June 2012 we were fortunate to be selected for funding following review by a NASA grant panel.
It can be a challenge to design an ISS experiment with the highest chance of success, given the constraints of the container size to be flown and minimal level of astronaut involvement. This limited capacity necessitates careful planning to ensure the inclusion of proper controls and enough replicates for robust statistical analysis of results. Arabidopsis (thale cress, or mouse-ear cress) is the plant we will use for our experiment, due to its small size and our extensive knowledge of its physiology and genetics thanks to decades of Arabidopsis research by the plant biology community.
Low oxygen, also called hypoxia, can be a problem for life in space and is a focus of our research. Without gravity, there is no convection and so mixing of gasses can be reduced. This in turn can lead to local increases in carbon dioxide and decreases in oxygen directly next to a living plant or animal. For example, imagine if the air movement fans on the ISS stopped running. The astronaut’s exhaled air (with depleted oxygen and high carbon dioxide) could form a “balloon” around their head. Likewise, in the absence of air movement around the plant, gases could locally build up or become depleted. For the aerial portion of the plant this problem can be minimized with the use of fans, however, what about roots where forcing movement and mixing through substrate is much harder? When grown in microgravity, roots are thought to experience low oxygen stress. We wish to address two questions with our experiment. First, do plants in space really suffer from significant low oxygen stress? Secondly, can we alleviate this problem using biological counter-measures without having to resort to costly and difficult engineering-based solutions?
Gilroy Lab postdoc Won-Gyu Choi, in the course of doing other experiments, discovered that the Arabidopsis plant survives better at low oxygen levels if it lacks a particular protein. The protein is a calcium transporter, and it is involved in moving calcium ions across the membranes of a plant cell. How this missing protein enables survival of the plant at low oxygen is not well understood, and we are currently designing ground-based research to further investigate this question.
Our experiment on the ISS will compare the growth and gene expression (transcriptome) in microgravity of two varieties of wild type Arabidopsis and four varieties of Arabidopsis lacking particular calcium transport proteins. These six varieties will be grown on nutrient gel (phytagel) in small circular petri plates that fit into special containers called Petri Dish Fixation Units (PDFU); five PDFU will then be placed into NASA’s hardware called Biological Research In Canisters (BRIC). In addition to the seeds and phytagel, the PDFU also will hold the liquid “fixative” which will be added to the plants after 8 days of growth on the ISS to preserve them for analysis after return to Earth.
NASA calls our experiment BRIC-17, also known as the Test Of Arabidopsis Space Transcriptome (TOAST).
We are grateful to have the opportunity to put TOAST on the space station and hope to contribute to our knowledge and understanding of how plants cope with the challenges of growing in microgravity. It will be a interesting journey and I hope to convey the experience to you with regular blog updates about our efforts and other plant-related space science. Check back often to see our progress and results!