Defining the NAM Regulon for Gene Targets to Biofortify Crop Iron, Zinc, and Protein Concentrations.

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 nutritional value, 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.