Characterizing short and long term iron stress responses in iron deficiency tolerant and susceptible soybean (Glycine max L. Merr.)

Authors: ATENCIO, LEORRIE - Iowa State University; Salazar, Justin; Moran Lauter, Adrienne; GONZALES, MICHAEL - University Of Georgia; O`Rourke, Jamie; Graham, Michelle

Submitted to: Plant Stress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2021
Publication Date: 4/24/2021
Citation: Atencio, L., Salazar, J., Moran Lauter, A., Gonzales, M.D., O'Rourke, J.A., Graham, M.A. 2021. Characterizing short and long term iron stress responses in iron deficiency tolerant and susceptible soybean (Glycine max L. Merr.). Plant Stress. 2.Article 100012. https://doi.org/10.1016/j.stress.2021.100012.
DOI: https://doi.org/10.1016/j.stress.2021.100012

Interpretive Summary: Iron is a micronutrient essential for the proper growth and development of all organisms. In plants, lack of usable iron can result in iron deficiency chlorosis (IDC), which is characterized by yellowing of the leaves, reduced plant growth and lower yield. Soybeans grown in the upper Midwestern United States often suffer from IDC. Our research takes advantage of two soybean lines that are 98% genetically identical, but differ in their iron stress response. Clark plants are iron efficient and tolerant to iron stress, while Isoclark plants are iron inefficient and develop symptoms of IDC under iron stress conditions. To understand the molecular mechanisms contributing to iron stress responses, we grew Clark and Isoclark seedlings in normal growth conditions for ten days, in normal growth conditions for eight days followed by two days of iron stress, or for ten days in iron stress conditions. We then collected root and shoot tissue for whole genome expression analysis. This allowed us to identify thousands of genes whose activity changed directly in response to iron stress. These analyses demonstrate the importance of genes involved in cell cycle, gene silencing, iron acquisition and defense in the Clark iron stress response. In addition, they suggest soybean is using novel mechanisms to allow continuous signaling between source and sink tissues. These findings improve our understanding of the genes and networks underlying plant stress tolerance which can be leveraged by researchers to improve stress tolerance in soybean and other important crop species.

Technical Abstract: Iron Deficiency Chlorosis (IDC) is a disease caused by lack of useable iron in the soil. Symptoms include stunting and interveinal chlorosis of the leaves, eventually leading to end of season yield loss. IDC is important in the upper Midwestern United States because calcareous soils favor its development. Using high throughput sequencing approaches, we characterized soybeans’ short and long-term response to iron stress. Our research leverages two near isogenic lines that are 98% genetically identical but differ in their iron efficiency response. Clark is iron efficient and tolerant to iron stress, while Isoclark is iron inefficient and develops IDC symptoms under iron stress. Plants were grown in one of three treatments: iron sufficient media for ten days, iron deficient media for ten days, or iron sufficient media for eight days then transferred to iron deficient media for two days. RNA-seq analysis identified genes differentially expressed in response to short and long term iron deficiency in both genotypes and the transcription factors regulating their expression. These analyses demonstrate the importance of genes involved in cell cycle, gene silencing, iron acquisition and defense in the soybean iron stress response. In addition, they suggest novel mechanisms for signaling between source and sink tissues.