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Title: Survey of ferric reductase transcription and activity in Pisum sativum accessions

item Grusak, Michael

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/31/2008
Publication Date: 10/11/2008
Citation: Klein, M., Grusak, M.A. 2008. Survey of ferric reductase transcription and activity in Pisum sativum accessions [abstract]. XIV International Symposium on Iron Nutrition and Interactions in Plants, October 11-16, 2008, Beijing, China. p. 81.

Interpretive Summary:

Technical Abstract: Iron (Fe) is an essential element for the growth of plants. While Fe is not limiting in most soils (it makes up approximately 5% of total soil minerals), Fe availability to plants in aerated, calcareous soils near neutral or basic pH can be severely limited as Fe oxidizes to form less soluble ferric hydroxide precipitates. Under conditions of low Fe availability, dicot and non-graminaceous monocot plants induce a three-part Fe accumulation response to mobilize Fe within the rhizosphere and move it into the roots, referred to as Strategy I. Strategy I includes acidification of the rhizosphere via proton pump activation, reduction of Fe(III) to Fe2+ through a plasma membrane bound ferric reductase, and increased uptake of Fe2+ by Fe2+ transporters localized to the plasma membrane of the root epidermis. Physiological studies in pea (Pisum sativum) suggest that the reduction of Fe is the rate-limiting physiological process in Fe acquisition for Strategy I plants. In order to understand the regulation of ferric reductase in plants, a number of studies have been conducted with the bronze (brz) and degenerative leaflet (dgl) pea mutants. These pea mutants display iron deficient root phenotypes (high levels of ferric reductase activity, increased Fe transport into root tissue) even under iron-replete growing conditions, leading to excessive iron accumulation in shoot tissue. Grafting experiments with these mutant lines demonstrate constitutive expression of FRO1, the ferric reductase in roots of plants, suggesting that shoot-based signals play a role in the regulation of Fe uptake in roots. Additional work in Arabidopsis suggests that both transcriptional and translational regulation play a role in the activity of ferric reductase. In order to further dissect the regulation between ferric reductase transcription and activity, and to take advantage of the iron homeostasis mutants available in pea, we have undertaken a survey of pea accessions to characterize ferric reductase transcription and activity. Thirty different pea accessions representing genotypes from a worldwide range of environmental locations were obtained from the USDA Agricultural Research Service's Pisum Germplasm Collection. These plants were grown under low and high Fe conditions (0.5 and 15uM Fe(III)-EDDHA) and analyzed for root Fe reductase activity and FRO1 transcript abundance via quantitative RT-PCR. While transcript studies are still ongoing, initial reductase activity assays show variable activity both between and within pea accessions. The correlation between transcriptional FRO1 levels and ferric reductase activity under both low and high Fe media conditions will be shown and discussed as a means to modify or further understand Fe homeostasis and regulation at the whole plant level.