MIMOSINE-FE(III) PEPTIDE TRASPORTERS IN LEUCAENA LEUCOCEPHALA

Mimosine, a non-protein amino acid produced by the tree legume Leucaena leucocephala (leucaena), has been considered to be a phytosiderophore for the uptake of Fe³⁺ by the plant. Leucaena secretes mimosine to the rhizosphere, where it binds to Fe³⁺. Kinetic studies in our lab have shown that three molecules of mimosine bind to one molecule of Fe³⁺ to produce a stable mimosine-iron complex, which is taken up by the plant as a mechanism for iron acquisition. Sequestering and uptaking of iron are especially important in alkaline soils. Under high pH conditions, micronutrients such as iron, zinc, copper and manganese become chemically bound with other soil nutrients, rendering them insoluble and unavailable, or only sparingly available for plant use. These micronutrients are needed as cofactors in many enzymes and their deficiencies lead to inhibition of plant growth. The goal of this research is to identify the mechanism of transport of the mimosine-iron complex into the leucaena root system. It has been hypothesized that a large complex made up of three mimosine and one Fe³⁺ will require a peptide transporter for transporting into the plant cell. There is currently no report on how higher plants, such as leucaena, acquire iron under high pH conditions in the absence of mugineic acid, which is widely studied in monocots and members of the grass family. The specific objectives of this project are: (i) to identify peptide transporters in leucaena; and (ii) to identify the specific peptide transporter(s) for mimosine-iron complex. Thirteen peptide transporter partial sequences were identified from the transcriptome sequences of leucaena on the basis of sequence homology with known peptide transporters, analyzed using BLAST. The lengths of the sequences ranged 260-1990 bp, while their homologies with green plants peptide transporters ranged 72-89%. The full-length cDNA sequences for these transporters will be obtained using 5’ and 3’ Rapid amplification of cDNA ends (RACE). We expect that the transporter for the mimosine-iron complex will be expressed exclusively in the roots. Therefore, the expression level of the thirteen transporters will be determined in leaves, stems, and roots of leucaena by quantitative reverse transcription polymerase chain reaction (qRT-PCR) followed by gel electrophoresis and UV imaging of PCR products. Discovering the mechanism of iron acquisition will be useful for developing plant varieties suitable for growing in alkaline soils.