Patterns of Arabidopsis gene expression in the face of hypobaric stress [Experiment 2]

Extreme hypobaria is a novel abiotic stress that is outside the evolutionary experience of terrestrial plants. In natural environments, the practical limit of atmospheric pressure experienced by higher plants is about 50 kPa or ~.5 atmospheres; a limit that is primarily imposed by the combined stresses inherent to high altitude conditions of terrestrial mountains. However, in highly controlled chambers and within extra-terrestrial greenhouses the atmospheric pressure component can be isolated from other high altitude stresses such as temperature, desiccation, and even hypoxia. In addition, hypobaria can be carried to extremes beyond what is possible in terrestrial biomes, and explored as a single variable in the examination of plant responses to novel stress. Previous studies have shown that plants adjust to hypobaric stress by differentially expressing suites of genes in unique combinations that are not equal to the dissected components of hypobaric stress (such as hypoxia and desiccation). Here we examine the organ-specific progression of transcriptional strategies for physiological adaptation to hypobaric stress over time. An abrupt transition from a near-sea level pressure of 97 kPa to only 5 kPa is accompanied by the differential expression of hundreds of genes. However, the transcriptomic reaction to hypobaric conditions lying between these two extremes reveals complex, organ-specific responses that vary over a time course of hypobaric exposure, and that are also not linear with respect to a simple gradient of severity. It is also clear that plants adjust over time such that the gene expression patterns that are initially elicited to cope with hypobaria are mediated as plants adjust their metabolism to this environment. The patterns of genome-wide changes in gene expression across a gradient of atmospheric pressures, and over a time course of several days allows for the development of theories of how plant metabolisms may be adapting to changes in atmospheric pressures.

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