Uncovering Transcriptional Responses to Fractional Gravity in Arabidopsis Roots

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.