Submitted to: Plant Physiology and Biochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/7/2007
Publication Date: 5/1/2007
Citation: O'Rourke, J., Graham, M.A., Vodkin, L., Gonzalez, D., Cianzio, S., Shoemaker, R.C. 2007. Recovering from iron deficiency chlorosis in near isogenic soybeans: a microarray study. Plant Physiology and Biochemistry. 45:287-292. Interpretive Summary: Soybeans grown on high pH soils in the upper midwest often suffer from a deficiency of iron. This results in a yellowing of the young plants. Although the plants may return to a normal appearing green color later in the growing season there often seems to be a reduction in yield, presumably related to iron deficiency. In this paper the authors measured levels of gene expression in soybean lines that differ only in their ability to respond to iron deficiency. They deprived both lines of iron until yellowing ocurred, then added sufficient iron for the plants to recover. They determined that although both the lines greened up and seemed normal after receiving adequate iron, the inefficient line had at least four genes that continued to be expressed different from the efficient line. These genes may reflect modification in the metabolism of the inefficient line that may be related to the reduced yield at maturity. This information will be useful to breeders and geneticists who are attempting to understand the mechanisms associated with iron stress.
Technical Abstract: Iron deficiency chlorosis (IDC) 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. IDC susceptible 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, iron efficient PI548553 (Clark) and iron inefficient PI547430 (IsoClark), developed for their response to iron deficiency stress (22.) 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. RNA was isolated from root tissue and transcript profiles were examined between the two near- isogenic lines using publicly available cDNA microarrays. By alleviating the iron deficiency stress our expectation was that plants would return to baseline expression levels. However, the microarray comparison identified four cDNAs that 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 and confirmed by real time PCR experimentation. Control experiments showed that these genes are not differentially expressed in plants grown continually under iron rich hydroponic conditions. The expression differences suggest potential residual effects of iron deficiency on plant health.