Natural variation among Arabidopsis thaliana accessions in tolerance to high magnesium supply

High magnesium (Mg(2+)) in some extreme serpentine soils or semi-arid regions is an important factor affecting crop growth and development. Specific loci that form the genetic framework underlying high Mg(2+) homeostasis, however, are not well understood. By using GWA mapping on 388 accessions of Arabidopsis thaliana selected from a worldwide collection and genotyped at approximately 250,00 SNPs, we successfully identified 109 and 74 putative genetic regions associated in nutrient traits under normal (1,000 µM) and high Mg(2+) (10,000 µM), respectively. Above 90% SNPs associated with nutrients including Mg(2+) and only two SNPs shared between normal and high Mg(2+). A single strong peak of SNPs associated with Ca concentration corresponding to candidate gene At1g60420 ARABIDOPSIS NUCLEOREDOXIN (AtNRX1) under high Mg(2+) was further determined. Compared with wildtype, mutants of Atnrx1-1 and Atnrx1-2 supplied with high Mg(2+) had higher Ca concentrations in the plant, and higher cytosolic Ca(2+) concentrations during root elongation, as well as higher fresh weight and lateral-root number. This suggests that AtNRX1 was a critical gene negatively regulating Ca uptake under high Mg(2+) conditions. The discovery could help to breed/select crops that can adapt to high-Mg(2+) soils such as serpentine soils (high ratio of Mg(2+): Ca(2+)) or Mars soil with high levels of magnesium sulfate.