Systemic phloem signals for compatibility or defence in response to fungal infections in Zea mays and Hordeum vulgare

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Goal of this project is to catch phloem-borne signals responsible for systemic induced susceptibility (SIS) and metabolic redirection upon pathogen attack. Direct collection of phloem samples may be one promising approach to find these unknown compounds. Based on literature data and a series of preliminary experiments, we reached the conclusion that calcium may be a neglected essential element in longdistance signalling. In this study, the yield of micro-sampling of phloem sap will be improved and the collection methods adapted to the pathosystems. The phloem sap will be screened for shifts in composition between infected and non-infected compatible plant lines. Plant/fungus systems will be Zea mays/Ustilago maydis, Zea mays/Colletotrichum graminicola, Hordeum vulgare/ Blumeria graminis and Hordeum vulgare/Piriformospora indica. In the chase for candidate signals, we will first focus on Ca2+-conjugates and jasmonic acid and its relatives. In a second wave of analyses, sugars, oxygen radicals and the redox state of the sieve tube sap will be tested. The last analytical part will include the detection of macromolecules such as proteins, protein complexes and several RNA-forms. With the techniques at hand, we may be able to trace compounds responsible for both compatibility and resistance by the same set of experiments.