Iron deficiency stress can induce MxNRAMP1 protein endocytosis in M. xiaojinensis

• A full-length cDNA sequence of MxNRAMP1 was obtained from M. xiaojinensis.
• MxNRAMP1 was up-regulated in leaves and roots after iron deficiency stress.
• MxNRAMP1 was located in the plasma membrane and vesicles in M. xiaojinensis.
• MxNRAMP1 transported iron ions via vesicle endocytosis after iron deficiency.
• Overexpression of MxNRAMP1 promoted iron absorption and accumulation.

BackgroundIron deficiency is one of the most common nutritional disorders in plants, especially in fruit trees grown in calcareous soil. Iron deficiency stress can induce a series of adaptive responses in plants, the cellular and molecular mechanisms of which remain unclear. NRAMPs (natural resistance-associated macrophage proteins) play an important role in divalent metal ion transportation.ResultsIn this study, we cloned MxNRAMP1, an NRAMP family gene from a highly iron-efficient apple genotype, Malus xiaojinensis. Further research showed that iron deficiency stress could induce MxNRAMP1 expression in roots and leaves. A protoplast transient expression system and immune electron microscopy localization techniques were used to prove that MxNRAMP1 mainly exists in the plasma membrane and vesicles. Interestingly, iron deficiency stress could induce the MxNRAMP protein to transport iron ions to specific organelles (lysosome and chloroplast) through vesicle endocytosis. Stable transgenic tobacco showed that MxNRAMP1 over-expression could promote iron absorption and accumulation in plants, and increase the plant's resistance against iron deficiency stress.ConclusionsThese results showed that, in M. xiaojinensis, MxNRAMP1 not only plays an important role in iron absorption and transportation, it can also produce adaptive responses against iron deficiency through endocytosis.