Abstract
Although many reports characterize the transcriptional response of Arabidopsis seedlings to microgravity, few investigate the effect of partial or fractional gravity on gene expression. Understanding plant responses to fractional gravity is relevant for plant growth on lunar and Martian surfaces. The plant signaling flight experiment utilized the European Modular Cultivation System (EMCS) onboard the International Space Station (ISS). The EMCS consisted of two rotors within a controlled chamber allowing for two experimental conditions, microgravity (stationary rotor) and simulated gravity in space. Seedlings were grown for 5 days under continuous light in seed cassettes. The arrangement of the seed cassettes within each experimental container results in a gradient of fractional g (in the spinning rotor). To investigate whether gene expression patterns are sensitive to fractional g, we carried out transcriptional profiling of root samples exposed to microgravity or partial g (ranging from 0.53 to 0.88 g). Data were analyzed using DESeq2 with fractional g as a continuous variable in the design model in order to query gene expression across the gravity continuum. We identified a subset of genes whose expression correlates with changes in fractional g. Interestingly, the most responsive genes include those encoding transcription factors, defense, and cell wall-related proteins and heat shock proteins.
Highlights
Plant cultivation will be essential during long duration space missions to supplement nutritional needs of the crew, purify air and water, and provide psychological benefits to the crew [1]
One rotor within the European Modular Cultivation System (EMCS) was kept stationary and the second rotor was set to a rotational speed so as to simulate ‘1 g’
We have shown that select genes appear to respond to a narrow gradient of fractional g ranging from 0.53 g to 0.88 g
Summary
Plant cultivation will be essential during long duration space missions to supplement nutritional needs of the crew, purify air and water, and provide psychological benefits to the crew [1]. One unfamiliar stress that spaceflight and extraterrestrial environments pose to plant growth is the lack of or reduced gravity. Since both the Moon and Mars have gravitational fields that are a fraction of Earth’s gravity, partial gravity research is especially relevant to near term space exploration [2]. Partial gravity can be simulated on Earth through the use of clinostats affixed with centrifuges [4], with the same limitations as simulating microgravity. In addition to providing a ‘1 g’ control for flight experiments, programmable centrifuges, such as the (recently decommissioned) European Modular Cultivation System (EMCS) on the International Space Station (ISS), allowed for the generation of partial gravitational forces during spaceflight
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