Elucidating the Function in Iron Homeostasis and Transport of the VTL Family of Vacuolar Membrane Proteins in Arabidopsis

• Applicant: Professor Thomas J. Buckhout, Ph.D.
• Subject Area: Plant Physiology
• Term: from 2011 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 194980302

In the continuation of the project we wish to pursue the investigation of the functions of VTL proteins in iron homeostasis and to establish whether the VTL transporters are suitable tools for increasing the iron storage capacity in plants. The following goals will be pursued. 1. Investigation of the Transport Characteristics of the VTL Proteins and their intracellular localization We have multiple lines of evidence that indicate the presence of the VTL proteins on the vacuolar membrane and that they play an important role in iron homeostasis. Complementation of the ccc1 mutant by heterologous expression of VTL1, 2 or 5 lends further support for their roll in vacuolar transport and homeostasis of iron. It is necessary, however, to demonstrate iron transport directly and to determine the kinetic properties of transport by the VTLs. We propose accomplishing this by iron transport assays using vacuoles isolated from yeast cells that over-express the VTL genes. In parallel to heterologous expression, intracellular localization of the VTL proteins will be investigated. 2. Optimizing Iron Storage in Plants. A goal that is being pursued also by others is to increase the iron storage capacity of plants. Obtaining this goal would produce hardier plants and crops with improved nutritional value for food and fodder. We feel that with the VTL transporters we have additional possibilities for increasing iron in plants. We have published increased iron content in nramp3/nramp4 mutant seeds that over-express VTL1, 2 or 5 (Gollhofer et al., 2014). We have unpublished data showing that VTL2, 4 and 5 over-expression lines, now in the third generation, have from 50 to 100% higher iron in seeds than the Col wild-type. Thus, over-expression of the VTL genes can lead to an increased iron storage capacity. We wish to extend these findings and combine them with unique approaches to increase the iron content of seeds, and thereby develop a model for engineering an increase in plant iron for a wide range of plant species. 3. Screening for Improved Growth on Poorly Available Iron. Beginning in the Fall of 2015 and continuing for one academic year Prof. Wolfgang Schmidt will be on sabbatical leave from the Academia Sinica at the Institute of Biology, Humboldt-Universität zu Berlin. In my laboratory we will conduct a screening of Arabidopsis ecotypes for their ability to grow on poorly available iron sources (e.g. FeCl3 at pH 7.0). Recently, the spectrum of iron mobilization strategies has been expanded to include synthesis and secretion of phenolic compounds in Arabidopsis (Rodríguez-Celm et al., 2013; Schmid et al., 2014). This phenolic based uptake strategy is likely important for iron uptake in neutral and alkaline soils, and it may be the mechanism behind resistance to lime-/bicarbonate-induced chlorosis in crop plants. Our goal is to identify new players that permit plant growth on poorly available iron soils.

• DFG Programme: Research Grants
• International Connection: Taiwan
• Co-Investigator: Professor Dr. Wolfgang Schmidt