Submitted to: Iron Nutrition and Interactions in Plants Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 11/3/2006
Publication Date: 7/3/2007
Citation: O'Rourke, J.A., Graham, M.A., Cianzio, S.R., Shoemaker, R.C. 2007. Recovering from iron deficiency chlorosis in near isogenic soybeans: a microarray study [abstract]. Iron Nutrition and Interactions in Plants Symposium. Paper No. S6-P-21. Interpretive Summary: Some varieties of soybean have a lessened ability to draw the essential nutrient, iron, from the soil. This causes a yellowing of the plant. Even though the plants may eventually re-green, they often exhibit reduced yield. In this study the authors mimicked this situation by creating an iron stress in plants, and then adding iron so that they re-greened. By comparing soybean varieties that are efficient at drawing iron from the soil with varities that are inefficient, they discovered several genes whose expression does not recover to the pre-stressed level. This may explain why some varieties exhibit reduced yield even though they seemingly have recovered from iron stress. This information will be useful to molecular geneticists and breeders who are attempting to develop soybean varieties with stable yield even on soil with unavailable iron.
Technical Abstract: Iron deficiency chlorosis in soybeans has proven to be a perennial problem in the calcareous soils of the U.S. upper Midwest. A historically difficult trait to study in fields, the use of hydroponics in a controlled greenhouse environment has provided a mechanism to study genetic variation while limiting environmental complications. Plants growing in calcareous soils and in iron-controlled hydroponic experiments, often exhibit a characteristic chlorotic phenotype early in the growing season but are able to re-green later in the season. To examine the changes in gene expression of these plants, near isogenic lines, PI548553 (iron efficient) and PI547430 (iron inefficient), developed for their response to iron deficiency stress (USDA-ARS National Genetic Resources Program 2004) were grown in iron-deficient hydroponic conditions for one week, then transferred to iron sufficient conditions for another week. This induced a phenotypic response mimicking the growth of the plants in the field; initial chlorosis followed by re-greening. Root tissue was collected and transcript profiles were examined between the two near- isogenic lines using publicly available cDNA microarrays. By alleviating the iron deficiency stress we hypothesized plants would return to baseline expression levels. However, the microarray comparison identified four cDNAs which were under-expressed by a two-fold or greater difference in the iron inefficient plant compared to the iron efficient plant. This differential expression was re-examined by real time PCR experimentation. We believe the expression differences suggest long-lasting effects of iron deficiency on plant health, which is reflected by reduced yield. The functional annotation of these differentially expressed genes may help us to better understand the role of iron transport and iron metabolism in soybean health.