Elucidating Salicylic Acid Sensing in Biotrophic Smut Fungi

Ustilago maydis is a biotrophic pathogenic fungus that causes tumours on all aerial parts of maize plants. With the help of numerous small secreted proteins, so called effectors, this pathogen is able to subvert plant defence responses and to manipulate the host metabolism for its own needs. While the perception of the pathogen by the plant is quite well investigated, little is known how the pathogen senses the defence status of its host in order to secrete the appropriate effector cocktail keeping the balance in the biotrophic interaction. We recently discovered that U. maydis is able to sense the important plant defence hormone salicylic acid (SA). This opens up the possibility that the fungal invader reads along the plant defence status via SA. With an SA-responsive promoter reporter construct in U. maydis we performed a mutagenesis screen to identify components of the fungal SA sensing machinery. Preliminary results with several mutant candidates provided a proof-of-concept. In this project we suggest strategies to dissect this novel SA signalling cascade and to functionally characterize its components. We will further include the related smut fungus Ustilago bromivora that infects the model plant Brachypodium distachyon, to test if fungal SA signalling components have orthologous functions in other smuts as well. This will allow additional experimental approaches and enables us in the future to explore fungal SA perception as a target for plant protection.

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