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Title: Identification of QTL affecting seed mineral concentrations and content in the model legume Medicago truncatula

item Grusak, Michael

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2009
Publication Date: 7/1/2009
Citation: Sankaran, R.P., Huguet, T., Grusak, M.A. 2009. Identification of QTL affecting seed mineral concentrations and content in the model legume Medicago truncatula. Theoretical and Applied Genetics. 119:241-253.

Interpretive Summary: Plant seeds are an important dietary source of micronutrient and macronutrient minerals. Legume seeds, in particular, have the potential to provide a significant proportion of those minerals that are essential for human growth, development, and health maintenance. In order to ensure that our agronomic legumes are providing the optimal concentrations of essential minerals, it is important to understand the genetic basis for mineral concentrations in seeds and the rate-limiting steps involved in the whole-plant distribution of minerals. This information will enable us to breed and develop more nutritious legumes. In order to assist in this effort, we analyzed seed mineral concentrations in 169 genetically unique plant lines, derived from two parent cultivars of the model legume, Medicago truncatula. We also analyzed the genetic make-up of each of these lines, and using specialized statistical tests we were able to identify regions of the plant's genome (that is, the positions along the DNA strands) that were associated with elevated concentrations of iron, zinc, manganese, copper, calcium, magnesium, phosphorus, and potassium. We also identified genomic regions associated with increased seed weight. This information will help us to identify the specific genes that are responsible for the nutrient-related seed traits. Ultimately, the information derived from Medicago truncatula will be used to breed for enhanced seed mineral concentrations in several important crop legumes.

Technical Abstract: Increasing the amount of bioavailable micronutrients such as iron and zinc in plant foods for human consumption is a challenge, especially in developing countries where plant foods comprise a significant portion of the diet. Legume seeds have the potential to provide the essential nutrients required by humans. However, the concentrations of minerals such as Fe and Zn are low when compared to other foods. In order to increase seed mineral concentration, it is important to understand the genetic basis for mineral concentration in the seeds and the rate limiting steps involved in mineral distribution. To determine the loci governing seed mineral concentrations, seed mineral content, and average seed weight in a model legume, 169 lines of a Medicago truncatula RIL population (Jemalong-6 x DZA 315.16) were grown for seed harvest for subsequent seed mineral analysis of Ca, Cu, Fe, K, Mg, Mn, P, and Zn using ICP-OES in 2004 and 2006. QTL cartographer was used to identify quantitative trait loci (QTL) using composite interval mapping (CIM). Transgressive segregation was observed for nearly all the minerals, suggesting multiple gene action and that the traits were truly quantitative. In both years, significant correlations between different minerals were observed, which might indicate cosegregation of genes for different minerals. CIM identified a total of 46 QTL for seed mineral concentration, 26 for seed mineral content, and 3 for average seed weight. At least one QTL was detected for each mineral trait. In both years, colocation of QTL for several minerals was found, which might indicate that common whole plant phenotypic traits such as transpiration efficiency or common transporters might be contributing to seed mineral levels. Our results comparing seed weight with seed mineral concentration and content QTL suggest that seed size can be an important determinant of seed mineral concentration, and correlations based on content can unmask the effects of seed size on seed mineral concentration.