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

High magnesium (Mg) 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 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 (10,000 µM), respectively. Above 90% SNPs associated with nutrients including Mg and only two SNPs shared between normal and high Mg. A single strong peak of SNPs associated with Ca concentration corresponding to candidate gene At1g60420 ARABIDOPSIS NUCLEOREDOXIN (AtNRX1) under high Mg was further determined. Compared with wildtype, mutants of Atnrx1-1 and Atnrx1-2 supplied with high Mg had higher Ca concentrations in the plant, and higher cytosolic Ca 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 conditions. The discovery could help to breed/select crops that can adapt to high-Mg soils such as serpentine soils (high ratio of Mg: Ca) or Mars soil with high levels of magnesium sulfate.