DETERMINATE

Compared to mammals, indeterminate growth and post-embryonic developmental plasticity are key features of land plants. Identifying the molecular networks that fine-tune determinacy and indeterminacy in growth is key to understanding the evolution of diverse plant structures. Legumes engage in mutualism with nitrogen-fixing rhizobia, within facultative, specialized organs called root nodules, which exhibit either indeterminate or determinate growth depending on the persistence of apical cell division. In legumes, nodule indeterminacy is the ancestral trait, which independently evolved at least three times towards a derived determinacy state. The DETERMINATE project hypothesizes that these repeated transitions toward nodule determinacy involve similar gene regulatory networks (GRNs) and reflect a case of convergent evolution. DETERMINATE is organized into three work packages combining the expertise of three partners in bioinformatics, comparative genomics, transcriptomics, single-cell techniques, molecular biology and functional genetics. WP1: phylotranscriptomics and phylogenomics integrating available datasets and a well-chosen set of species will be used to identify GRNs involved in the regulation of nodule growth transitions and to test the convergent evolution hypothesis. WP2: cross-species integration of single-nuclei RNA-seq data will allow the reconstruction of cell trajectories of determinate and indeterminate nodules and to draw a spatio-temporal map of the mechanisms controlling determinacy and cell identities in nodules. WP3: nodule cell identities will be visualized using a novel in situ RNA hybridization method and selected candidates controlling nodule determinacy will be functionally tested. DETERMINATE’s knowledge gained on nodule developmental plasticity and indeterminate growth GRNs will offer insights into the broader principles of plant development and evolution.