Martian regolith (unconsolidated surface material) is a potential medium for plant growth in bioregenerative life support systems during manned missions on Mars. However, hydrated magnesium sulfate mineral levels in the regolith of Mars can reach as high as 10 wt%, and would be expected to be highly inhibitory to plant growth. A global approach was used to identify novel genes with potential to enhance tolerance to high MgSO4 stress. The early Arabidopsis root transcriptome response to elevated concentrations of magnesium sulfate was characterized in col-0, and also between col-0 and the mutant line cax1-1 – a mutant relatively tolerant of high levels of MgSO4•7H2O in soil solution. Overall design: After 3 weeks of growth under hydroponic conditions, Arabidopsis thaliana col-0 roots were exposed to a basic nutrient solution (0.25 g/L MES, 1/16x MS, pH 5.7) with an additional 2.08 mM magnesium sulfate (total Ca:Mg ratio = 1:15) for 45 min., 90 min., or 180 min., while a col-0 control set was exposed to the basic nutrient solution without additional magnesium sulfate for 45 minutes. Arabidopsis thaliana cax1-1 roots were exposed to the basic nutrient solution with additional magnesium sulfate for 180 min. only. Four replicate containers were harvested for the control and each of the treatment sets, resulting in a total of 20 samples. Gene expression of the col-0 sets exposed to magnesium sulfate treatment for 45 min., 90 min., or 180 min. was compared to gene expression of the col-0 control set. Gene expression of the cax1-1 set exposed to magnesium sulfate treatment for 180 min. was compared to gene expression of the col-0 set exposed to magnesium sulfate treatment for 180 minutes.