MicroRNA- and transcription factor profiling: analyzing two regulatory steps of plant cell reprogramming in response to arbuscular mycorrhizal (AM) colonization

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The mechanisms leading to the rapid and profound reprogramming of plant cells during the arbuscular mycorrhizal (AM) symbiosis are largely unknown. The proposed projects will analyze two major levels of the regulatory network of plant cells to determine their involvement in the response to AM colonization: transcription factors (TFs) and microRNAs (miRNAs). In plants, both regulatory mechanisms are tightly linked, since the majority of plant miRNAs characterized so far target TFs and regulate their expression and activity. Deep sequencing of small RNA and degradome tags of mycorrhizal and nonmycorrhizal M. truncatula roots revealed hundreds of novel M. trunctula miRNAs and miRNA-cleaved mRNAs. MiRNAs with induced abundance in mycorrhizal roots or with mRNA-cleavage targets known to be involved in root endosymbioses will be characterized in the proposed project. In parallel, we will continue the analysis of two degradome libraries in order to detect mRNAs with specific miRNA-mediated degradation pattern in mycorrhizal roots. In the second part of the project we identified TFs with an arbuscule-related expression as well as TFs induced upon diffusible signals deriving from a mycorrhizal root organ culture. These TFs are now characterized by expression perturbation analysis, localization and concerning their downstream targets using an inducible expression system. To extend our insight in the first responses of a plant cell after perception of signals from AM fungi, we plan a deep sequencing of RNA from isolated root epidermal cells.