Unravelling the transcription factor network controlling the biosynthesis of tryptophan-derived antimicrobial compounds in Arabidopsis roots and shoots

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As an efficient defense strategy, plants produce secondary metabolites with antimicrobial properties to defeat invading microorganisms. In the model plant Arabidopsis, camalexin and indole-glucosinolates (IGs) are both derived from the primary metabolite tryptophan (Trp) and have been demonstrated to inhibit growth of various plant pathogens. The complex biosynthetic pathway leading to Trp-derived secondary compounds is highly coordinated on transcriptional level and therefore, provides an excellent model system for studying transcriptional regulatory networks. Several transcription factors (TFs) have been identified to control the metabolic pathway genes in the above-ground part of the plant. Preliminary results support the notion that the TFs operating in roots differ from leaves and are yet completely unresolved. This project aims to identify putative transcriptional master regulators of the complete and of specific branches of Trp-derived secondary metabolism comparing root and leaf tissues. To identify novel regulators in roots, a high-throughput screening system in root protoplasts (Protoplast Trans Activation, PTA) will be applied enabling analysis of more than 1500 Arabidopsis TFs. Candidate TFs will be functionally characterized by inducible gain- and loss-of-function approaches with respect to the TF impact on target gene regulation, direct promoter binding using Chromatin Immunoprecipitation (ChIP), regulatory promoter cis-elements, altered metabolite profile and pathogen defense. Combining pre-existing knowledge with data on the newly identified TFs, we aim to disclose the hierarchical regulatory TF networks underlying co-ordinated transcriptional regulation of this crucial metabolic pathway in plant defense. Moreover, insights in these regulatory circuits will support further attempts to engineer disease resistant crop plants.