Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2012
Publication Date: 4/1/2012
Citation: Peiffer, G.A., King, K.E., Severin, A.J., May, G.D., Cianzio, S.R., Lin, S., Lauter, N.C., Shoemaker, R.C. 2012. Identification of candidate genes underlying an iron efficiency QTL in soybean. Plant Physiology. 158(4):1745-1754. Interpretive Summary: Although iron is the fourth most abundant mineral in the earth's crust, it remains a limiting nutrient for plants and for human nutrition. The uptake of iron by plants requires a complex interaction of many genes. Often, the identity of the genes is unknown and the location of the genes on chromosomes is only imprecisely estimated. Obtaining the identity of these genes will contribute greatly to improved crop production and improved nutritional value of many crops. In this study, the authors used classical and molecular genetics to uncover the gene probably responsible for a major effect on iron efficiency in soybean. The gene is a small regulatory piece of DNA that is involved in triggering a cascade of gene effects resulting in improved iron balance. This finding will help soybean breeders select for cultivars with improved iron efficiency which will result in the saving of hundreds of millions of dollars per year for producers; savings that are usually lost due to iron deficiency chlorosis.
Technical Abstract: Prevalent on calcareous soils in the United States and abroad, iron deficiency is among the most common and severe nutritional stresses in plants. In soybean commercial plantings, identification and use of iron efficient genotypes has proven to be the best form of managing this soil-related plant stress. Previous studies conducted in soybean identified a significant iron efficiency QTL explaining > 70 % of the phenotypic variation for the trait. In this research we identified candidate genes underlying these QTL through molecular breeding, mapping and transcriptome sequencing. Introgression mapping was performed using two related near-isogenic lines in which a region located on soybean chromosome 3 required for iron efficiency was identified. The region corresponds to the previously reported iron efficiency QTL. The location was further confirmed through QTL mapping conducted in this study. Transcriptome sequencing and qRT-PCR identified, two genes encoding transcription factors within the region that were significantly induced in soybean roots under iron stress. The two induced transcription factors were identified as homologs of the subgroup lb bHLH genes in that are known to regulate the strategy I response in A. thaliana. Re-sequencing of these differentially expressed genes unveiled a significant deletion within a predicted dimerization domain. We hypothesize this deletion disrupts the FIT / bHLH heterodimer that has been shown to induce known iron acquisition genes.