Function of GRAS transcription factor complexes in arbuscular mycorrhizal symbiosis

• Applicant: Dr. Katharina Melkonian-Ezekian
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536856410

Arbuscular mycorrhizal symbiosis (AMS), the mutualistic association between arbuscular mycorrhizal fungi (AMF) and plants, has a fundamental impact on terrestrial ecosystems and health of individual plant species. The AMS is characterized by specialized symbiosis structures named arbuscules, which are formed by the symbiont inside plant cells and enable the efficient exchange of nutrients and other molecules. The initiation, establishment and maintenance of a functional AMS is regulated by a very specific transcriptional program that is activated in colonized plant tissues. The research conducted in vascular plants has demonstrated that multiple transcription factors (TFs) of the GRAS gene family are involved at different steps of this transcriptional program and that different GRAS protein complexes are contributing to different aspects of a functional symbiosis. The GRAS gene family is highly duplicated and diversified in vascular plants. Functional redundancy and high numbers of paralogs complicate a detailed mechanistic analysis of GRAS TFs in vascular plants. Thus, potential functions of many GRAS TFs during AMS are currently unknown and it is poorly understood how the specific known functions of each GRAS TF during AMS are achieved. A long-standing hypothesis has been that diverse and dynamic protein complexes involving GRAS TFs assemble to regulate each step of the AMS. Additionally, it remains to be determined whether known functions of GRAS TFs in AMS are evolutionary conserved across land plants. The liverwort Marchantia paleacea has been developed as the first non-vascular plant model capable to form AMS. Marchantia liverworts exhibit low genetic redundancy, which is a major advantage for a mechanistic functional dissection of genes that are highly duplicated in other model plant species, like the GRAS gene family. The aim of this project is to understand how GRAS family TFs regulate AMS in M. paleacea. Using a combination of loss and gain of function approaches, as well as interactomics and transcriptomics, I will investigate the function of GRAS TFs belonging to different subclades during AMS, elucidate the protein complexes they form and test the contribution of these complexes for activating cell reprogramming enabling the AMS. The knowledge gained from my studies will provide insights into specific functions of GRAS proteins during AMS in M. paleacea and likely discover new functions of GRAS TFs that are potentially conserved in other land plants. In addition, the generated dataset will be a novel resource for the community to facilitate the understanding of AMS, the most ancient plant symbiosis.

• DFG Programme: WBP Fellowship
• International Connection: France
• Host: Professor Dr. Pierre-Marc Delaux