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Research project of the team

Published on 24 January 2019

We employ various developmental genetics, molecular biology and biochemistry approaches to study
(i) the dynamics of chromatin landscapes during developmental transitions,
(ii) novel chromatin activator activities and their mechanisms,
(iii) nuclear and sub-cellular mechanisms associated with chloroplast biogenesis

Our strategy should allow understand the crosstalk between chromatin structure, transcription factor binding and communication between sub-cellular compartments, phenomenons often studied independently even though they are closely linked in the regulation of plant developmental transitions.

Dynamics of chromatin activation: temporal and spatial resolution at the developing flower
Plant ontogeny is associated with highly flexible cell fates that allow organogenetic programs to take place throughout the plant lifespan. During organogenesis, small clusters of stem cells acquire new fates before differentiating into specific cell types. Such events are initiated by the activation of developmental genes specific to clusters of cells that will give rise to specific organ primordia. We aim at deciphering the molecular events that take place at the level of the chromatin and underlie this transition. To this end, we develop and exploit new methodologies enabling a genome-wide analysis of chromatin activation dynamics. Our model of study is the Arabidopsis floral meristem for which genetic tools enable the isolation of synchronized tissues and/or specific tissue types, in large amounts. This permits to follow, in vivo, the transcriptional status of floral developmental genes at different stages of flower development.

Characterization of novel transcriptional and chromatin activators
We previously showed that ULTRAPETALA1 (ULT1), a plant-specific chromatin activator, induces gene expression through the removal of chromatin repressive marks. Taking ULT1 as an anchor, our goal is to identify novel transcriptional activators and characterize their molecular assembly during flower development in Arabidopsis. To that aim, we use (1) yeast-two-hybrid screen (2) Bimolecular Fluorescent Complementation and (3) in planta immuno-precipitation approaches.
Meta-analysis of binding maps for ULT1 and ULT1 partners, together with chromatin features will allow temporal resolution of their assembly and function during gene activation events.

Molecular and sub-cellular mechanisms associated with chloroplast biogenesis
Chloroplasts develop from proplastids in meristem cells but little is known about the genetic determinants of their biogenesis. The Plastid­Encoded RNA­Polymerase (PEP) complex, which is essential for building the photosynthetic apparatus, is profoundly reshaped during the dark-to-light transition, with the addition of 12 nuclear subunits named PAP (PEP-Associated Proteins), bringing the chimeric complex to a 1.1-MDa structure. Mutations in any PAP lead to albino/ivory or pale­-green plants with an arrested plastid development in which no or minor PEP activity is detected. We aim at deciphering the role of the PAPs in the nucleus, what is their trafficking route and whether they support retrograde signaling. The potential nuclear sub-complex contains PAPs with signature domains (DNA binding domains, SET methyltransferase domain), which indicate a role in gene expression and/or chromatin modification. Our goals are (1) in planta purification and characterization of PAP complexes; (2) uncoupling the subcellular functions of the bi-localized PAPs; (3) functional analysis of nuclear PAPs (chromatin binding profiles, influence on chromatin marks, effect on histone methylation status); and (4) assessing PAP trafficking from chloroplast to nucleus with a tag-based tracing system.