Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/15/2007
Publication Date: 11/12/2007
Citation: Vasconcelos, M.W., Lopez-Millan, A., Li, G.W., Musetti V., Grusak, M.A. 2007. Cloning and functional characterization of MtFRO1, a root iron reductase from Medicago truncatula [abstract]. 6th European Conference on Grain Legumes, November 12-16, 2007, Lisbon, Portugal. p. 110.
Technical Abstract: Iron is an essential micronutrient, and although it is abundant in the soil, it can be poorly available under certain soil conditions. The activity of the Fe(III) reductase enzyme, an integral plasma membrane protein belonging to the super-family of the flavocytochromes (1), is the rate-limiting physiological process in root Fe-acquisition (2). The objectives of this study were: 1) to clone the major iron-induced reductase gene from Medicago truncatula; 2) to correlate MtFRO1 expression with levels of reductase activity; 3) to test the functionality of MtFRO1 in a yeast heterologous system; 4) to analyze MtFRO1 transcription in different Medicago tissues; and 5) to identify other candidate genes that are important in the plant’s response to iron limitation. We identified eight putative FRO sequences through database searches, and we analyzed their expression in roots and shoots of plants grown in iron deficiency. We then cloned the cDNA that encodes an iron-responsive root ferric iron reductase from Medicago roots (MtFRO1). Reductase activity in Medicago was low in iron sufficiency and higher in plants grown with limited iron (0.5 µM Fe). Expression of MtFRO1 cDNA in the yeast mutant strain fre-2, which has a defective yeast ferric reductase, restored its growth on low Fe media and conferred this strain an increased Fe reductase activity. Also, the expression of the MtFRO1 transcript in roots was up regulated in low Fe conditions and down-regulated when plants were resupplied with sufficient iron. MtFRO1 transcripts were detected in peduncules, stems, flowers, cotyledons and roots, but not in leaves, suggesting that leaf iron reduction is either performed by a different FRO, or it is strongly dependent on photoreduction. The expression pattern of several nputative metal-related genes, based on tentative consensus sequences from Medicago, were studied in roots and shoots by semi-quantitative RT-PCR. The expression profiles for several of these candidates were found to be up-regulated by iron deficiency and down-regulated with iron resupply.