Chemical signaling in mycorrhizal symbiosome development in Lotus japonicus

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The proposed project focuses on the chemical and molecular interaction between arbuscular mycorrhizal (AM) fungi and the legume Lotus japonicus in late developmental stages of the AM symbiosis, i.e. during formation of the symbiosome which is the site where bi-directional exchange of nutrients and metabolites takes place. In mycorrhizal plants, P uptake in the form of orthophosphate (Pi) across the plasma membrane of AM fungus and host plant is mediated by membrane intrinsic fungal and plant Pi transporter proteins. The contribution of the mycorrhizal Pi uptake pathway compared to that of direct Pi uptake from the soil solution can dominate total plant P uptake almost completely. The molecular basis of this pathway’s regulation is still poorly understood. A primary goal of this project is therefore to characterize plant and/or fungal chemical signal(s) which are involved in triggering mycorrhiza-specific Pi transporter gene expression. The use of mass spectrometry based technologies has been instrumental to identify the first lipid signal in AM Pi transport and is central to this project for identification and further characterization of signal molecules in the AM symbiosis. In 2011, the applicant’s laboratory will be equipped with an Applied Biosystems (ABI Sciex) QTRAP 5500 coupled to a NanoMate system for direct infusion of lipid samples which will allow in depth analysis of mycorrhizal lipid extracts and identification of phospholipid compounds discovered via their mass peaks through nanoESI-MS/MS. An integrated comparative approach based on lipid and transcript profiling will enable exploration of the molecular basis of plant and fungal lipid metabolism underlying AM symbiosis. The second part of this project, aims at unravelling the evolutionary conserved mechanisms underlying transcriptional regulation of plant Pi transporter genes during formation of the AM symbiosome in L. japonicus and other plant species. This includes a continuation of our work on the identification of cis- and trans-acting factors directing promoter activity of respective AM-specific genes. Here, the overall goal is to characterize the many genes the coordinated expression of which is required to build an AM symbiosome.