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Title: Effects of Fe deficiency on the riboflavin synthesis pathway in medicago truncatula plants

item LOPEZ-MILLAN, ANA-FLOR - Consejo Superior De Investigaciones Cientificas (CSIC)
item RODRIGUEZ-CELMA, JORGE - Consejo Superior De Investigaciones Cientificas (CSIC)
item ABADIA, ANUNCIACION - Consejo Superior De Investigaciones Cientificas (CSIC)
item Grusak, Michael
item ABADIA, JAVIER - Consejo Superior De Investigaciones Cientificas (CSIC)

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2010
Publication Date: 6/26/2010
Citation: Lopez-Millan, A., Rodriguez-Celma, J., Abadia, A., Grusak, M.A., Abadia, J. 2010. Effects of Fe deficiency on the riboflavin synthesis pathway in medicago truncatula plants [abstract]. 15th International Symposium on Iron Nutrition and Interactions in Plants. p. 114.

Interpretive Summary:

Technical Abstract: Riboflavin was first described to be excreted from roots of Fe-deficient tobacco plants and since then excretion and accumulation of riboflavin, as well as other flavin compounds has been reported in a wide variety of plant species. In flavinogenic yeast strains and some bacteria, Fe has been shown to down-regulate riboflavin synthesis. In plants, the exact role these flavin compounds play in Fe deficiency and the mechanisms causing their accumulation are still not known. The two major hypotheses are a role in the reducing power supply to the Fe reductase and an antimicrobial effect in the rizosphere. The aim of this work was to study the expression of genes involved in the riboflavin biosynthetic pathway as affected by Fe deficiency, in order to determine the key step(s) in the Fe-mediated riboflavin synthesis regulation. Plants were grown in Fe-sufficient nutrient solution (45 uM Fe-EDTA) and in two Fe-deficient (0 uM Fe-EDTA) nutrient solutions, either with Ca carbonate (high pH), or without Ca carbonate (low pH). Roots from Fe-sufficient plants were white and roots from Fe-deficient plants were yellow. Root morphology in the two Fe-deficiency treatments was different, with swollen yellow tips at high pH, and swollen tips (only some of them yellow) and yellow patches along their length at low pH. Genes encoding for GTP cyclohydrolase II (GTPc), ribD, 6, 7-dimethyl-8-ribityllumazine synthase (DMRL), and riboflavin synthase (ribE) were identified, cloned, and sequenced, and the resulting amino acid sequences shared 50-70% homology with those of Arabidopsis. All the proteins presented conserved domains related to their proposed biological function. The effects of Fe deficiency on the expression of these genes in roots was studied by qPCR. Quantification showed that expression of all the genes of the pathway was induced by Fe deficiency in both low and high pH conditions, and that inductions were higher when plants were grown at high pH. DMRL showed the highest induction (24- and 100- fold in low and high pH, respectively) followed by GTPc (11- and 32- fold). These results suggest that DMRL and GTPc might be key enzymes controlling Fe-deficiency induced riboflavin accumulation in roots.