Research Article Patterns of Arabidopsis gene expression in the face of hypobaric stress Anna-Lisa Paul 1† , Mingqi Zhou 1† , Jordan B. Callaham 1 , Matthew Reyes 2 , Michael Stasiak 3 , Alberto Riva 4 , Agata K. Zupanska 1 , Mike A. Dixon 3 and Robert J. Ferl 1,4 * 1 Program in Plant Molecular and Cellular Biology, Department of Horticultural Sciences, University of Florida, Gainesville, FL 32611, USA 2 Exploration Solutions, Inc., Moffett Field, CA 94035, USA. 3 University of Guelph, Guelph, N1G 2W1 ON, Canada. 4 Interdisciplinary Centre for Biotechnology, University of Florida, Gainesville, FL 32610, USA. Received: 18 November 2016; Editorial decision: 19 June 2017; Accepted: 3 July 2017; Published: 7 July 2017 Associate Editor: Michael B. Jackson Citation: Paul A-L, Zhou M, Callaham JB, Reyes M, Stasiak M, Riva A, Zupanska AK, Dixon MA, Ferl RJ. 2017. Patterns of Arabidopsis gene expression in the face of hypobaric stress. AoB PLANTS 9: plx030; doi:10.1093/aobpla/plx030 † These authors share first authorship. Abstract. 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 about 0.5 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 projected extra-terrestrial greenhouses, the atmospheric pressure component can be isolated from the associated high altitude stresses such as temperature, desiccation and even hypoxia. Such chambers allow the exploration of hypobaria as a single variable that can be car- ried to extremes beyond what is possible in terrestrial biomes. Here, we examine the organ-specific progression of tran- scriptional strategies for the physiological adaptation to various degrees of hypobaric stress, as well as the response to severe hypobaria over time. An abrupt transition from a near-sea level pressure of 97 kPa to a mere 5 kPa is accompa- nied by the differential expression of hundreds of genes, primarily those associated with drought, hypoxia and cell wall metabolism. However, pressure transitions between these two extremes reveals that plants respond with complex, organ-specific transcriptomic responses, which also vary over time. These responses are not linear; neither with respect to the gradient of hypobaric severity from 75, 50, 25 to 10 kPa, nor with the duration of exposure of up to 3 days at 10 kPa. In the first few hours of hypobaria, plants engage changes in basic metabolism and hormonally mediated growth and development. After 12 or more hours of hypobaria, the gene expression patterns are more indicative of hypoxia and drought environmental responses. The hypobaria transcription patterns were highly organ specific, and roots appeared to be more sensitive to hypobaria than shoots in that the number of differentially expressed genes was higher in roots than in shoots. The patterns of gene expression among organs, across a gradient of atmospheric pres- sures and over time suggest that plants adapt to the novel stress of pure hypobaria by using recognizable metabolisms to meet appropriately interpreted hypoxia stresses, while engaging drought responses that are seemingly inappropri- ate to the wet and humid environment of the chambers. Keywords: Abiotic stress; Arabidopsis; hypobaria; hypoxia; Mars greenhouse; reduced atmospheric pressure. * Corresponding author’s e-mail address: robferl@ufl.edu V C The Authors 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/ licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is prop- erly cited. AoB PLANTS www.aobplants.oxfordjournals.org V C The Authors 2017 100 Downloaded from https://academic.oup.com/aobpla/article/9/4/plx030/3934080 by guest on 17 January 2022