Cell-specific reprogramming of legume roots for endosymbiotic infection

• Applicant: Professor Dr. Martin Parniske
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems ; Plant Cell and Developmental Biology
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 258665719

The vast majority of land plants can establish arbuscular mycorrhiza (AM), an agronomically important symbiosis with fungi to improve mineral and water supply. Legumes use an ancient signal transduction program, co-opted from the ancestral AM, to establish intracellular (endosymbiotic) interactions with nitrogen-fixing rhizobia, in the root nodule symbiosis. Successful symbiotic infection relies on an ancient cellular differentiation program for the intracellular accommodation of the microsymbionts. Although a number of important symbiosis genes essential for the infection process have been identified through genetic approaches, the precise cellular and molecular events underlying bacterial colonization of the root are poorly understood. The COME-IN project will focus on nuclear signalling events and associated transcriptional reprogramming that take place in host cells engaged in rhizobial infection. By developing cutting-edge cell imaging strategies in living cells, the Toulouse team has recently shown that calcium-spiking and the localized accumulation of the symbiotic ERF transcription factor (TF) ERN1 are specific nuclear responses which are associated with the early stages of infection. By pushing the technologies one step further, this project aims to decipher the spatio-temporal interconnection between calcium-spiking and the dynamics of TF accumulation and complex conformation preceding host cell transcriptional reprogramming for infection. We will focus on the two key infection-related TFs ERN1 and CYCLOPS, the latter acting in a complex with CCaMK, an important early integrator of calcium signalling. The Munich team has observed that CYCLOPS phosphorylation is essential for its transcriptional activity, and is associated with structural alterations of the CYCLOPS dimer. FRET-based strategies will be used to follow CYCLOPS complex formation in living cells during infection and how this correlates with calcium signalling. The Munich team has found the CYCLOPS promoter to be critical for successful symbiotic signalling. We will identify the cis- and trans-acting factors that determine the complex expression pattern of CYCLOPS. We will employ the INTACT (Isolation of Nuclei TAgged in specific Cell Types) technology to specifically target the small subpopulation of cells undergoing reprogramming and couple it with RNA sequencing to access gene transcription networks specifically associated with early stages of rhizobial infection. The comparison of cell-specific transcriptomes of wild type and infection-deficient mutants will aid in the identification of genes directly related to endosymbiotic entry. The COME-IN project will thus provide new insights into the cellular reprogramming during endosymbiotic root colonization.

• DFG Programme: Research Grants
• International Connection: France
• Participating Person: Dr. Fernanda de Carvalho-Niebel