Dept. of Biological Sciences

Erin Connolly

Associate Professor of Biological Sciences

Ph.D. 1997 University of California, Davis
803-777-8753
erinc@biol.sc.edu

Molecular Genetics of Metal Uptake in Plants

Certain metals, like iron, zinc and manganese, are essential nutrients for animals, plants and microbes. Other metals, like cadmium, are toxic and the accumulation of these metals can pose a serious threat to ecosystems and human health. Iron deficiency is the most common human nutritional disorder in the world today. The World Health Organization estimates that over 3 billion people worldwide suffer from iron deficiency. Despite the fact that plants serve as the principal source of iron in most diets worldwide, most crops contain low amounts of bioavailable iron. In addition, low iron availability often limits plant growth, resulting in reductions in yield. Although plants require iron for normal growth and development, iron can also be toxic if accumulated to high levels. Thus, as iron levels in the soil change, plants must maintain a balanced intracellular supply of iron. As a result, iron acquisition is a highly regulated process. Our long-term goal is to define the molecular mechanism of metal ion uptake in plants. In particular, we are focusing on the regulatory mechanisms that control iron uptake in the model plant, Arabidopsis.

All plants except the grasses respond to iron-deficiency using a two-step process. Extracellular Fe(III) is reduced to the more soluble Fe(II) by a plasma membrane bound Fe(III) chelate reductase. We recently identified a gene (FRO2 for Ferric Reductase Oxidase) that encodes a root-specific plasma membrane bound Fe(III) chelate reductase in Arabidopsis (Robinson et al., 1999). The resulting Fe(II) is then transported across the root epidermal cell membrane by a Fe(II) transporter; recent work described the cloning of the first Fe(II) transporter (IRT1 for Iron-Regulated Transporter) from a plant. We are taking a combined molecular, genetic and biochemical approach to study the regulation of these and other genes whose products are necessary for the acquisition of iron.

These studies should aid in the design of transgenic plants that are capable of vigorous growth on soils with low iron availability. In addition, one of our long-term goals is to engineer plants that specifically accumulate elevated levels of iron and thus, have a higher nutritional value. We are also studying uptake of the toxic metal cadmium by IRT1 with the goal of designing transgenic plants that can be used to clean up sites contaminated with heavy metals like cadmium.

Selected Publications:

Ciftci-Yilmaz S., Morsy M.R., Song L., Coutu A., Krizek B.A., Lewis M.W., Warren D., Cushman J., Connolly E.L., Mittler R. (2007). The EAR-motif of the Cys2/His2-type zinc finger protein Zat7 plays a key role in the defense response of Arabidopsis to salinity stress. J. Biological Chemistry 282: 9260-9268.

Mukherjee, I., Campbell, N.H., Ash, J.S. and Connolly, E.L. (2006). Expression profiling of the ferric chelate reductase (FRO) Gene Family reveals differential regulation by iron and copper. Planta 223:1178-1190.

Durrett. T.P. Connolly, E.L. and Rogers, E.E. (2006). Arabidopsis cpFtsY mutants exhibit pleiotropic defects including an inability to increase iron deficiency-inducible root Fe(III) chelate reductase activity. The Plant Journal 47(3): 467-479.

Kerkeb, L. and Connolly, E.L. (2006). Iron transport and metabolism in plants. In: Genetic Engineering, Principles and Methods. Vol. 27, J.K. Setlow ed. Kluwer Academic Publishers. pp. 119-140.

Connolly, E.L. Campbell, N., Grotz, N., Prichard, C., and Guerinot, M.L. (2003). Overexpression of the FRO2 ferric chelate reductase confers tolerance to growth on low iron and uncovers post-transcriptional control. Plant Physiol. 133:1102-1110.

Connolly, E.L. Fett, J. and Guerinot, M.L. (2002). Expression of the IRT1 metal transporter is controlled by metals at the levels of transcript and protein accumulation. The Plant Cell 14(6): 1347-1357.

Connolly, E.L. and Guerinot, M.L. (2002). Iron stress in Arabidopsis -- is Genomics Revealing? Genome Biology. 3(8): reviews 1024.1-1024.4.

Robinson, N.J., Proctor, C.M., Connolly, E.L.and Guerinot, M.L. (1999) A ferric-chelate reductase for iron uptake from soils. Nature 397: 694-697.

Connolly, E.L.and Guerinot, M.L. (1998) Reduction and Uptake of Iron in Plants. In: Plasma Membrane Redox Systems and their Role in Biological Stress and Disease. H. Asard, A. Berczi and R. Caubergs, Eds. Kluwer Academic Publishers.

Grotz, N., Fox, T., Connolly, E., Park, W., Guerinot, M.L. and Eide, D. (1998) Identification of a family of zinc transporter genes from Arabidopsis thaliana that respond to zinc deficiency. Proc. Natl. Acad Sci USA 95(12):7220-7224.

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