Symposium V: From the soil to the seed

Abs # 50004: From the soil to the seed: metal transport in Arabidopsis

Presenter:	Guerinot, Mary Lou , Guerinot@Dartmouth.edu
Authors	Guerinot, Mary Lou  (A)
Affiliations:	(A): Department of Biological Sciences, Dartmouth College, Hanover, NH 03755

Increasing the ability of plants to take up minerals could have a dramatic impact on both plant and human health. Furthermore, understanding the pathways by which metals accumulate in plants will enable the engineering of plants to exclude toxic metals or to extract toxic metals from the soil. We have employed the tools available in the model plant Arabidopsis to identify genes involved in metal homeostasis. We had previously identified IRT1, a root specific transporter that is expressed in the plasma membrane of epidermal cells under iron deficiency and is responsible for uptake of iron from the soil. Like other iron transporters identified to date, IRT1 transports a variety of cations, including essential metals such as zinc and manganese as well as the toxic metal cadmium. Using molecular breeding, we have isolated mutant alleles of IRT1 that maintain iron transport yet support the survival of yeast on concentrations of cadmium well above normally toxic levels. We have begun to express mutant alleles of IRT1 in Arabidopsis to further examine this potential. As IRT1 belongs to the 15-member ZIP gene family in Arabidopsis, information from our IRT1 studies may be directly transferable to other members of this metal transporter family. We are currently addressing the role of each of the ZIP proteins in the transport of divalent cations throughout the plant. Both IRT1 and FRO2, the ferric chelate reductase, appear to be coordinately controlled in response to plant iron status. We have characterized an essential transcription factor, FIT1, that differentially regulates these two genes. In addition to studying iron uptake from the soil, we have also identified an iron transporter, CCC1, that localizes to the vacuolar membrane and is proposed to function in moving iron from the cytosol into the vacuole. When ccc1 loss of function mutants are treated with high levels of iron, the onset of toxicity is delayed relative to wild type, suggesting that CCC1 contributes to metal homeostasis. We are also using functional genomics approaches to identify genes involved in mineral homeostasis. Ion profiling via ICP-MS has identified a number of mutants with abnormal elemental compositions, including several that accumulate abnormally high levels of iron.