Plants provide a complete and economical means for human life support for long-term space exploration and habitation. However, since the space environment is not optimal for plant growth, an understanding of how plants sense and respond to changes in their environment is of fundamental importance. The phosphoinositide (PI) pathway is highly conserved among eukaryotes and functions in the regulation of a multitude of cellular pathways. The lipid-derived second messenger inositol 1,4,5-trisphosphate (InsP3) increases in response to many different stresses. We have shown that InsP3 levels increase with gravistimulation prior to visible bending in both monocot and dicot systems. We have generated transgenic Arabidopsis plants expressing the mammalian type I inositol polyphosphate 5-phosphatase (InsP 5-ptase), an enzyme that specifically hydrolyzes InsP3 and terminates the signal. The transgenic plants have normal growth and morphology; however, they exhibit altered responses to many environmental stimuli including gravity, drought, and cold. While rapid changes in transcript levels occur in wild type Arabidopsis within 5 min of gravistimulation, the expression of several of the fastest responding genes does not change in the InsP 5-ptase roots in response to reorientation.
Our hypothesis is that InsP3 is an important second messenger in the sensing and signaling of stimuli (including gravity). The plants with compromised InsP3 signaling therefore provide a valuable tool for dissecting the role of the InsP3 pathway in plant responses to the microgravity environment encountered on the International Space Station.
The long term goal is to understand the molecular mechanisms plants use to sense and respond to changes in their environment. This knowledge will help design plants which are better able to withstand space flight and microgravity conditions on long-term missions.
Plant Signaling will study the effects of various gravity levels on the growth responses of plants seedlings (roots and shoots; wild type and genetically modified). The objective of this experiment is to identify the molecular changes that are specifically mediated by InsP3 in the space environment. Transcript and protein profiles of wild type and transgenic plants that are grown in both microgravity and 1g in space as well as on the ground will be compared.
Images of seedlings will be captured and downlinked. Plant samples will be harvested and preserved on orbit for analysis on Earth.
In summary, our spaceflight results have demonstrated that significant transcriptional changes occur in microgravity in both wild type and InsP 5-ptase transgenic Arabidopsis seedlings and have uncovered regulatory mechanisms that are involved in plant adaptations to the microgravity environment. We are currently carrying out additional analysis and validation prior to preparation of manuscripts for publication. Based on these results, we were successful in obtaining funding in November 2014 for a subsequent flight opportunity to investigate the role of small RNAs in microgravity (NASA solicitation NNH14ZTT001N). We anticipate that these experiments will provide a comprehensive dataset that will be a valuable resource for other researchers in the field.
Data is available through GeneLab's Data Repository at https://genelab-data.ndc.nasa.gov/genelab/
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