Characterization of the AHA2 and IRT1 Iron Uptake Mutant Phenotypes in Arabidopsis thaliana

Iron (Fe) is an essential element throughout the plant’s life, from germination to seed development, as it serves as a co-factor for many enzymes. Although iron is a critical micronutrient, it is also a heavy metal. Plants can be susceptible to both an iron deficiency and an iron toxicity and therefore need to maintain optimal iron levels. Iron deficient plants become chlorotic and seed yield is low. Iron deficiency can also lead to an excess in other, more toxic metals such as Cadmium (Cd) and Copper (Cu). An excess amount of iron can result in toxicity which leads to stunted growth and dark green coloring in the leaves. Iron is insoluble in soil when pH is neutral or high, meaning that the roots can not take up free Fe. Decreasing the pH by adding hydrogen ions to the surrounding soil increases the amount of soluble free iron for uptake by the root. Higher plants, including the model organism Arabidopsis thaliana, decrease the pH of the surrounding soil to solubilize Fe, “mining” it to make it available for uptake. We plan to use A. thaliana in our experiment to study the iron uptake pathway. Two of the many genes in this pathway are AHA2 and IRT1. AHA2 decreases the soil pH by pumping hydrogen ions outside the cell and into the surrounding soil which increases the solubility of Fe. IRT1 is a metal transport protein which is reported to transport Fe, Cd, Manganese (Mn) and Zinc (Zn). We hypothesize that an insertion in these genes, AHA2 and IRT1, will have severe consequences in the plant phenotype and within the root microbial community which will be more visible under high pH conditions. To test the viability of the mutants, plants will be grown on square agar plates and the growth medium will have either a neutral pH, as a control, or a basic pH, to stimulate iron deficiency. We predict that the loss of any of these genes will result in a plant with signs of iron deficiency or toxicity which will lead to lower fitness under high pH conditions. Our work will help breed cover crops suitable for diverse and challenging soils of Vermont. We hope to obtain a better understanding of iron uptake in plants and to implement this knowledge in Medicago truncatula and other leguminous plants used in cover crop. With the data collected, we can work towards making plants, specifically legume cover crops, more suitable and resistant to dramatic climate changes