By Mary Lou Guerinot
Department of Biological Sciences
Dartmouth College, Hanover, NH 03755
11 December 2014, Thursday
Deficiencies of micronutrients such as iron and zinc commonly limit plant growth and crop yields. If the mechanisms of uptake, distribution, and regulation of micronutrients were clearly understood, it might be feasible to engineer plants to be better able to grow in soils now considered marginal and to increase crop biomass on soils now in cultivation. Furthermore, as most people rely on plants as their dietary source of micronutrients, plants that serve as better sources of essential nutrients would improve human health. 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. We are characterizing several new Arabidopsis mutants that have the potential to improve the iron content of seeds. One of these, Ig14, has a similar metal content to wild type when grown on normal soil, but thrives on alkaline soil, accumulating significantly more iron in its shoot and seeds. Another mutant, 93699, accumulates significantly more iron in the seed and shoots than wild type and is very sensitive to exogenous iron supply. The mutation in a third mutant has been mapped to an essential bHLH gene we call URI that controls many of the iron-regulated genes in Arabidopsis, including two redundant MYB transcription factors required for plant survival under low iron conditions.
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. We have been screening a large collection of rice cultivars and have identified several that have grain arsenic concentrations that place them in the tails of the observed distribution. Rice cultivars that restrict arsenic accumulation in the grain offer one of the simplest, fastest and most cost-effective approaches to solving the problem of arsenic contamination of rice and rice-based products. SXRF experiments have revealed that the different layers of the rice grain—each processed into different food products—contain different species of arsenic.