Identification of the magnesium transport (MGT) family in Poncirus trifoliata and functional characterization of PtrMGT5 in magnesium deficiency stress.

KEY MESSAGE: At least eight MGT genes were identified in citrus and PtrMGT5 plays important role in maintaining Mg homeostasis in citrus by getting involved in the Mg absorption and transport. Magnesium (Mg) is an essential macronutrient for plant growth and development, and the magnesium transporter (MGT) genes participate in mediate Mg2+ uptake, translocation and sequestration into cellular storage compartments. Although several MGT genes have been characterized in various plant species, a comprehensive analysis of the MGT gene family in citrus is still uncharacterized. In this study, eight PtrMGT genes were identified through genome-wide analyses. Phylogenetic analyses revealed that PtrMGT genes were classified into five distinct subfamilies. A quantitative RT-PCR analysis showed that eight PtrMGT genes were expressed in all of the detected tissues and they mainly expressed in the vegetative organs. Expression analyses revealed the PtrMGT genes responded to various Mg deficiency stresses, including absolute Mg deficiency and antagonistic Mg deficiency which caused by low pH or Al toxicity. PtrMGT5, which localizes to the plasma membrane and was transcriptionally active, was functionally characterized. PtrMGT5 overexpression considerably enhanced absolute Mg deficiency and antagonistic Mg deficiency tolerance in transgenic Arabidopsis plants, which was accompanied by increased fresh weight and Mg content, whereas opposite changes were observed when PtrMGT5 homolog in Valencia Orange callus was knocked down. Taken together, PtrMGT5 plays important role in maintaining Mg homeostasis in citrus by getting involved in the Mg absorption and transport.