Using computational methods, we analyzed gene activity (RNA-­-seq) in the iron efficient soybean line Clark, 1 and 6 hours after iron stress. We identified 974 genes that respond to iron stress in either leaves or roots. In the leaves, we are interested in transcription factors and signaling proteins that signal to the root that more iron is needed for continued growth and development. In the root, we are interested in the genes that receive the shoot signal and initiate the uptake of additional iron from the soil and genes that transport iron from the root to shoot. From this data, we developed 41 new VIGS constructs to characterize genes important in early IDC responses. If these genes are required for IDC tolerance, silencing them will make the plants more susceptible to IDC.

We have also taken advantage of data published by our group over the last ten years identifying hundreds of genes involved in IDC responses in IDC tolerant and susceptible lines. While the studies focused on late responses to IDC, they can still be used to identify genes that could improve or worsen IDC symptoms. By cross-­-referencing these experiments with the Soybean Virus Induced Gene Silencing (VIGS) website (http://soybase.org/SoyVIGS) we identified 130 VIGS constructs that were already available. So far, we have screened VIGS constructs for 52 different genes and 31 have yielded a visible phenotype ranging from alterations in growth, to reduced chlorophyll content and IDC-­-like symptoms. In addition, we have tested 14 of the VIGS constructs on plants grown in well watered and drought conditions to see if any of the genes are associated with drought tolerance. Five of the constructs altered the severity of drought symptoms relative to controls.

We have made significant progress over the first year of the project. A manuscript detailing the 1 and 6 hour gene expression data has been published. This manuscript highlighted soybean’s novel responses to IDC including sugar signaling in the leaves and the development of Casparian strips in the root. Both PIs have been invited to speak about the research at National and International Meetings. We are collaborating with other groups at Iowa State to determine if genes identified in this proposal protect against other plant stresses including pathogens. In addition, we are contributing to the training of undergraduate students by involving them in the analysis of expression data and VIGS screens.