Characterization of the main magnesium transporters mediating different Mg translocation from root to shoot between Mg-tolerant and Mg-sensitive Brassica napus cultivars under magnesium deficiency stress

Abstract

Magnesium (Mg) deficiency impacts many metabolic processes in Brassica napus (B. napus), leading to yield loss. However, the mechanism of Mg2+ uptake and translocation in B. napus remains unknown. After screening 39 genotypes of B. napus under Mg-deficient conditions, the cultivars P160 and P153 were selected according to their Mg transfer factor (TF) from root to shoot. We further characterized these two genotypes under Mg-deficiency by analyzing chlorophyll concentration, malondialdehyde and peroxidase activity, and reducing sugar concentration in leaves. Additionally, we performed transcriptomics and qRT-PCR assays on P153 and P160 shoots and roots. The identified functional genes involved in Mg transport were characterized by functional assays in yeast and Arabidopsis mutants. The physiological analysis revealed that P160 (Mg tolerance cultivar; Mg-T) is more tolerant than P153 (Mg sensitive cultivar; Mg-S) under magnesium-deficient environments. Transcriptomics and qRT-PCR assays revealed that transcript levels of BnMGT1–2 and BnMGT6–1 were more significantly up-regulated in the shoot of Mg-T cultivar than that of the Mg-S cultivar under Mg limitation. Functional assays of BnMGT1–2 and BnMGT6–1 reveals that BnMGT1–2 and BnMGT6–1 are the two main functional Mg transporters mediating Mg translocation from root to shoot under low Mg conditions. Mg-T is more efficient in the translocation of Mg from root to shoot than Mg-S. BnMGT1–2 and BnMGT6–1 should be the two main Mg transporters associated with Mg translocation under Mg deficiency condition, which caused the different Mg efficiency between the Mg-T and Mg-S.