Identification and characterization of MtMTP1, a Zn transporter of CDF family, in the Medicago truncatula

Zn is an essential micronutrient in plants, and the mechanisms of Zn homeostasis are under intensive study. In this report, we have identified MtMTP1, a Zn transporter of the CDF family in the legume model plant Medicago truncatula. The ORF of the MtMTP1 cDNA encodes a protein consisting of 407 amino acid residues with a predicted molecular mass of 45 kDa. Like other metal tolerance proteins (MTPs) in plants, heterologous expression of MtMTP1 can complement the Zn-susceptible zrc1 cot1 yeast double mutant. The expression pattern was studied by quantitative fluorescent PCR. The expression of MtMTP1 was detected in all vegetative organs with the highest level of expression observed in leaves. With Zn supplementation its expression in roots was reduced while its expression in stems was increased in the first 2 days. No obvious changes were detected in leaves. Inoculation with Rhizobium meliloti down-regulated its expression in roots.