The Effects of Simulated Martian Regolith on Arabidopsis Growth, Circadian Rhythms and Rhizosphere Microbiota

The environment on Mars dramatically differs from that on the Earth, including light, radiation, magnetic field and regolith, however, the effects of Martian regolith on plant growth, environmental fitness, circadian rhythm, and rhizosphere microbiota remains unclear. We grew Arabidopsis thaliana in simulated Martian regolith (SMR) and the changes in plant growth and development were observed. The changes in circadian rhythms of CCA1:LUC activity were monitored and transcriptomic expression was assessed by RNA sequencing (RNA-seq). 16S rRNA sequencing was carried out to analyze the rhizosphere microbiota. Arabidopsis grown in SMR displayed significantly repressed growth and rosette leaf development, and the seedlings died after 50 days with only one pair of euphylla. The plants grown in SMR showed an overall dramatically disrupted circadian rhythm. Growth in SMR led to changes in the rhythmicity of a subset of genes that regulate multiple pathways, including the circadian rhythm, porphyrin and chlorophyll metabolism. Furthermore, we identified genes associated with the circadian clock and metal metabolism. SMR contains lower absorbable contents of some basic elements, and supplementation with iron (Fe) partially restored the disturbed circadian phenotypes. Moreover, among the rhizosphere microbiota in SMR, the decreased abundance of Actinobacteria were observed, which may be associated with Fe metabolism. SMR may have deleterious effects on plant growth, uptake and metabolism of elements, and circadian clock. The low absorbable level of Fe in SMR may be one of the factors causing disruption of the plant’s circadian clock and the altered abundance of microorganisms.