From The Soil To The Seed: Metal Homeostasis In Plants.

Metal homeostasis is equilibrium between metal uptake and metal efflux, making metal transporters key players in controlling cellular metal content. Our long-term goal is to understand how plants acquire metals from the soil and distribute them while protecting themselves from the potential damage metals can cause to living tissues. We combine genetics, high throughput elemental analysis via inductively coupled plasma mass spectrometry (ICP-MS) and high resolution imaging via synchrotron X-ray fluorescence (SXRF) to identify and characterize genes involved in metal uptake, distribution and storage. 

Most of our work has been focused on the essential micronutrient iron.  More than 2 billion people are iron deficient because their plant-based diets are not a rich source of iron, making iron deficiency the most prevalent nutritional problem in the world today.  Clearly, we need to understand iron homeostasis in plants, both from the point of view of improving plant growth and crop yields as well as improving human nutrition. Our work on the vacuolar iron transporter, VIT1, established that proper iron localization in the seed is critical, as failure to store iron in the vacuole leads to seedling lethality under iron limitation. Overexpression of VIT1 in Arabidopsis increases iron storage in vacuoles, leading to leaf iron concentrations 5 fold higher than wild type. We also show that overexpression of VIT1 is accompanied by the up-regulation of FRO2 and IRT1, the high affinity iron uptake components of Arabidopsis. These findings suggest that exploiting the vacuole as a metal storage organ offers an avenue for increasing the iron content of plant-based diets.

We are also taking similar approaches to determine how arsenic, a non-threshold, Class 1 human carcinogen, accumulates in plants. Rice, a staple food for over half the world’s population, represents a significant dietary source of arsenic. SXRF experiments have revealed that the different layers of the rice grain – each processed into different food products – contain different species of arsenic.