Growth Performance and Root Transcriptome Remodeling of Arabidopsis in Response to Mars-Like Levels of Magnesium Sulfate

Abstract

BackgroundMartian 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.Methodology and Principal FindingsDisabling ion transporters AtMRS2-10 and AtSULTR1;2, which are plasma membrane localized in peripheral root cells, is not an effective way to confer tolerance to magnesium sulfate soils. Arabidopsis mrs2-10 and sel1-10 knockout lines do not mitigate the growth inhibiting impacts of high MgSO4·7H2O concentrations observed with wildtype plants. A global approach was used to identify novel genes with potential to enhance tolerance to high MgSO4·7H2O (magnesium sulfate) 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, which was confirmed to be relatively tolerant of high levels of MgSO4·7H2O in soil solution. Differentially expressed genes in Col-0 treated for 45 min. encode enzymes primarily involved in hormone metabolism, transcription factors, calcium-binding proteins, kinases, cell wall related proteins and membrane-based transporters. Over 200 genes encoding transporters were differentially expressed in Col-0 up to 180 min. of exposure, and one of the first down-regulated genes was CAX1. The importance of this early response in wildtype Arabidopsis is exemplified in the fact that only four transcripts were differentially expressed between Col-0 and cax1-1 at 180 min. after initiation of treatment.Conclusions/SignificanceThe results provide a solid basis for the understanding of the metabolic response of plants to elevated magnesium sulfate soils; it is the first transcriptome analysis of plants in this environment. The results foster the development of Mars soil-compatible plants by showing that cax1 mutants exhibit partial tolerance to magnesium sulfate, and by elucidating a small subset (500 vs. >10,000) of candidate genes for mutation or metabolic engineering that will enhance tolerance to magnesium sulfate soils.

Magnesium stress signaling in plant: Just a beginning

“…It was found that atmgt1 plants had almost similar biomass and leaf chlorophyll content with wild types under high Mg 2C stress (MgT) but the expression levels of AtMGT1, AtMGT7 and AtMHX were up-regulated in the wild type though non-significantly. 10 Although little change in the expression levels of these MgTRs were observed in microarray analysis when the plants were under MgSs, [8][9][10] results obtained from real time PCR detection showed significant changes for many MgTRs, for example AtMGT6 responding to Mg starvation. 30 We recently found that 8 AtMGTs and AtMHX were responding to MgT 1 and the findings were consistent with results obtained from serpentine conditions, where 6 MgTRs were highly expressed in the mesophyll and some could be correlated with higher accumulation of Mg in plants.…”

“…1,4,8 MgSs markedly inhibit plant growth, resulting in shorter roots, smaller shoots, and necrotic spots. 1,4,9,10,15,17,18 Hermans et al 4,8 found that MgD reduced the growth of young leaves more than the roots, but our results indicated that both root and leaf were severely inhibited by MgD (Fig. 1B) In addition to carbon fixation in photosynthesis, magnesium also acts as activator or cofactor of enzymes in carbohydrate metabolism, e.g., fructose-1,6-bisphosphatase (FBPase), glutamate synthetase, UDP-D-, ADP-D-, and GDPD-glucose pyrophosphorylase, and UDP-D-glucuronic acid pyrophosphorylase.…”

“…MgT significantly increases the transcriptional levels of many genes encoding enzymes in phytohormone biosyntheses, such as ABA (9-cis-epoxycarotenoid dioxygenase), ethylene (1-aminocyclopropane-1-carboxylate synthase) and jasmonic acid (lipoxygenase), 10 these are widely considered to mediate biotic or abiotic stress responses in plants. In Arabidopsis, we found that content of ABA increased more than 5 times in plants treated with MgT as compared to the untreated ones.…”

“…[5][6][7] Surprisingly, microarray studies revealed that the transcriptional levels of these plant MgTRs changed little under MgSs (deficiency or excess/toxicity), whereas, numerous other transporters were activated by MgSs. [8][9][10] However, the signal transduction responding to MgSs is largely unknown, although some reports indicated that expression levels of many genes related to phytohormone biosynthesis and signalings are significantly changed by MgSs. [8][9][10][11] Our previous studies discovered that at least 2 hormones, namely abscisic acid (ABA) and gibberellins (GA), and their signaling factors, DELLA and ABI1, are responding to magnesium toxicity (MgT).…”

“…[8][9][10] However, the signal transduction responding to MgSs is largely unknown, although some reports indicated that expression levels of many genes related to phytohormone biosynthesis and signalings are significantly changed by MgSs. [8][9][10][11] Our previous studies discovered that at least 2 hormones, namely abscisic acid (ABA) and gibberellins (GA), and their signaling factors, DELLA and ABI1, are responding to magnesium toxicity (MgT). 1 These results suggest that the discovery of signal transduction for MgT in plants could be a gateway to explore the regulatory mechanisms of responses to MgSs.…”