The meristematic regulatory network controlling the floral transition (BLOOM-NET)

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The overall aim of this project is to define the complex regulatory network that acts in the shoot apical meristem (SAM) to regulate the timing of transition to flowering, and to model quantitative and dynamic changes in this network during the floral transition.Several proteins with major functions in this process have been elucidated by genetic analyses in recent years. Nevertheless, the precise interplay and temporal behaviour, as well as the characteristics of the components that underpin the robustness of this regulatory system, have not been defined yet. This information is essential to predict the effects of mutations or environmental changes on flowering time. Ultimately, it will allow the adjustment of flowering time in crops of economic importance, and ensures that this transition occurs when required. We will focus on a sub-set of MADS box transcription factors (TFs) that have been shown to be the key regulators of the floral transition in the model species Arabidopsis thaliana. The exact timing of flowering is regulated by a tight balance between these transcriptional activators and suppressors. Our aim is to perform iterative cycles of wetlab experiments and modelling, to obtain comprehensive and quantitative data sets that lead to novel and testable hypotheses. Quantitative information derived from the wet experiments will be integrated in a simple wiring diagram describing all known qualitative interactions between the major regulatory components of the flowering system. Towards the end of the project this will lead to a mathematical model describing the regulatory steps controlling flowering time in the meristem. The following specific objectives are postulated:- Determine the concentrations of key-regulators (MADS proteins) in the shoot apical meristem (SAM) over time and link this to phenotypic output (i.e. the flowering time) under standard and perturbed conditions.- Obtain comprehensive binding site data-sets (i.e. target genes) of the various MADS-factors using a novel ChIP-SEQ approach.- Obtain the temporal transcriptome from the meristem of wild-type (WT) and mutant plants at various time points before and directly after the transition to reproductive development, and compare these data with the direct targets of TFs.- Determine the dimerization affinities of the MADS box TF molecules. Predict target sites at the genome level and model target site binding affinity and MADSfactor dimerization affinities.- Integrate the quantitative and qualitative aspects of the components of the network in a mathematical model that predicts the time of flowering as a function of balances between suppressors and activators.