Identification and Uses of Iron and Other Divalent Cations Transporters
Iron deficiency afflicts over 3 billion people worldwide, and plants are the principal source of iron in most diets. In response to iron deficiency, all plants except the grasses induce Fe(III) chelate reductase activity, Fe(II) transport activity and proton release into the rhizosphere. Dartmouth researchers have identified an Arabidopsis mutant, frd3, that constitutively expresses all three of these iron deficiency responses. Therefore, it is tempting to speculate that FRD3 encodes a regulatory factor involved in sensing and/or responding to iron levels in Arabidopsis. The FRD3 gene has been cloned; all three alleles of frd3 have single base pair alterations in a single open reading frame. FRD3 is predicted to encode an integral membrane protein 526 amino acids long, to contain 10 to 12 transmembrane domains and to be localized to the plasma membrane. It is a member of a large family of membrane proteins, the best characterized of which is the NorM gene from Vibrio parahaemolyticus. The NorM protein confers resistance to a variety of antibiotics and other toxic molecules, presumably through an energy-dependent efflux mechanism. Therefore, this protein family is known as the MATE (multi-drug and toxin efflux) family.
Experiments in pea have shown that there is a signal originating in the shoot that induces iron deficiency responses in the roots. Since FRD3, by RT-PCR, is expressed only in Arabidopsis roots, FRD3 may be the receptor for this shoot-derived signal. Alternately, FRD3 might be a transporter involved in transporting iron or a small signaling molecule into or out of root cells.
This discovery may be useful in engineering transgenic plants which can serve as nutritional supplements to treat iron or zinc deficiency, or remove pollutants from soil.
Dartmouth has filed a patent application covering this technology and is seeking an industrial partner who is interested in its commercialization. (Ref: J164
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