Under conditions of low iron (Fe) availability, dicots and non-graminaceous monocots up-regulate a root-specific three-part Fe acquisition response (referred to as Strategy I), which includes rhizosphere acidification via proton release, ferric iron reduction to the ferrous form, and ferrous iron transport at the root epidermis. Physiological studies completed in model plant species suggest that ferric iron reduction is the rate-limiting physiological process in Fe acquisition. Ferric reductase activity in plants is regulated at multiple levels. This study is part of a larger effort to understand how ferric reductase activity is regulated at the transcriptional and post-transcriptional levels. To that end, a survey of ferric reductase transcript levels (of the root-specific, iron-responsive PsFRO1) and root ferric reductase activity was conducted in a range of geographically diverse pea (Pisum sativum) plants grown in low and high Fe media to identify variation in iron acquisition responsiveness. Results indicate that reductase activity and PsFRO1 transcript levels vary across accessions even in iron replete growth conditions. Transcript abundance does not predict reductase activity across the accessions studied. The observed variation in PsFRO1 transcription and reductase activity seen across these lines, and the corresponding lack of correlation between these traits, suggests different mechanisms of ferric reductase regulation across the pea accessions. Accessions demonstrating iron status-responsive changes in ferric reductase transcription, with limited or no change in reductase activity (or non-responsive transcription with change in reductase activity) are of interest for future studies to identify the factors regulating ferric reduction in pea and other Strategy I plants.

Approximately half of the world population suffers from iron and/or zinc deficiency, and millions suffer from protein-energy malnutrition, primarily from reliance on plant based staple foods. These foods are low in iron, zinc, and protein density relative to animal based foods. We and others are interested in genetic improvement of plants to increase the nutritional value of plants, a strategy termed biofortification. In previous work, the NAM transcription factor genes of wheat were shown to regulate leaf senescence and iron, zinc, and nitrogen remobilization and translocation from vegetative tissues to grain. Thus, genes of the NAM transcription factor regulon are potential targets for nutritional improvement of cereal or other seed crops. As a first step to identify NAM regulated genes, we used the Affymetrix Wheat Genome microarray to profile genes that are differentially regulated in flag leaf tissue at mid-grain fill relative to anthesis, and that are also differentially regulated between control and NAM RNAi knockdown lines. Over three hundred genes met the criteria to be potential NAM targets, several of which are annotated as coding for proteins that could be involved in nutrient transport or protein metabolism. A highly homologous NAM gene with developmentally regulated leaf expression similar to wheat NAM genes was cloned from Sorghum bicolor. Results of genome-wide bioinformatic and molecular screens to identify potential NAM regulated genes and putative NAM response elements in gene promoters will be presented.