Project description:Plant development is controlled by transcription factors (TFs) which form complex gene-regulatory networks. Genome-wide TF DNA-binding studies revealed that these TFs have several thousands of binding sites in the Arabidopsis genome, and may regulate the expression of many genes directly. Given the importance of natural variation in plant developmental programs, there is a need to understand the molecular basis of this variation at the level of developmental gene regulation. However, until now, the evolutionary turnover and dynamics of TF binding sites among plant species has not yet experimentally determined. Here, we performed comparative ChIP-seq studies of the MADS-box TF SEPALLATA3 (SEP3) in inflorescences of two Arabidopsis species: A. thaliana and A. lyrata. Comparative RNA-seq analysis shows that the loss/gain of BSs is often followed by a change in gene expression.
Project description:Plant development is controlled by transcription factors (TFs) which form complex gene-regulatory networks. Genome-wide TF DNA-binding studies revealed that these TFs have several thousands of binding sites in the Arabidopsis genome, and may regulate the expression of many genes directly. Given the importance of natural variation in plant developmental programs, there is a need to understand the molecular basis of this variation at the level of developmental gene regulation. However, until now, the evolutionary turnover and dynamics of TF binding sites among plant species has not yet experimentally determined. Here, we performed comparative ChIP-seq studies of the MADS-box TF SEPALLATA3 (SEP3) in inflorescences of two Arabidopsis species: A. thaliana and A. lyrata. Comparative RNA-seq analysis shows that the loss/gain of BSs is often followed by a change in gene expression.
Project description:In angiosperms, flower patterning requires the localized expression of the APETALA3 (AP3) floral homeotic gene involved in petal and stamen development. AP3 is synergistically induced by the master transcription factor LEAFY (LFY) and the F-box protein UNUSUAL FLORAL ORGANS (UFO), but the molecular mechanism underlying this synergy has remained unknown. Here we show that the connection to ubiquitination pathways suggested by the F-box domain of UFO is mostly dispensable and that UFO instead acts by forming a transcriptional complex with LFY on newly discovered regulatory elements. The cryo-electron microscopy structure of the UFO-LFY-DNA complex shows that UFO-DNA contacts allows relocating LFY to novel DNA sites. Finally, we show that this complex has a deep evolutionary origin, largely predating flowering plants. This work unravels an unsuspected role for a member of one of the largest protein families in plants as a modulator of the DNA binding specificity of a master TF.
Project description:Floral organ identities in plants are specified by the combinatorial action of homeotic master regulatory transcription factors (TFs). How these factors achieve their regulatory specificities is however still largely unclear. Genome-wide in vivo DNA binding data show that homeotic MADS-domain proteins recognize partly distinct genomic regions, suggesting that DNA binding specificity contributes to functional differences of homeotic protein complexes. We used in vitro systematic evolution of ligands by exponential enrichment followed by high throughput DNA sequencing (SELEX-seq) on several floral MADS-domain protein homo- and heterodimers to measure their DNA-binding specificities. We show that specification of reproductive organs is associated with distinct binding preferences of a complex formed by SEPALLATA3 (SEP3) and AGAMOUS (AG). Binding specificity is further modulated by different binding site (BS) spacing preferences. Combination of SELEX-seq and genome-wide DNA binding data allows to differentiate between targets in specification of reproductive versus perianth organs in the flower. We validate the importance of DNA-binding specificity for organ-specific gene regulation by modulating promoter activity through targeted mutagenesis. Our study shows that intrafamily protein interactions affect DNA-binding specificity of floral MADS-domain proteins. DNA-binding specificity of individual dimers, as well as DNA-binding preferences of higher-order complexes differ between floral homeotic protein complexes. Differential DNA-binding of MADS-domain protein complexes plays a role in the specificity of target gene regulation.
Project description:Despite great advances in sequencing capacity, generating functional information for non-model organisms remains a challenge. One solution lies in an improved ability to predict genetic circuits based on primary DNA sequence combined with the characterization of regulatory molecules from model species. Here, we focus on the LEAFY (LFY) transcription factor, a conserved master regulator of floral development. Starting with biochemical and structural information, we built a biophysical model describing LFY DNA binding specificity in vitro that accurately predicts in vivo LFY binding sites in the Arabidopsis thaliana genome. Extending the model to other species, we show that it can correctly identify functional homologs of known LFY targets from Arabidopsis thaliana in other angiosperms, even if a functional shift between orthologs and paralogs has occurred. Moreover, this model demonstrates the evolutionary fluidity of the link between LFY and one of its target genes, underlining how this regulatory interaction can be conserved despite changes in position, sequence and affinity of the LFY binding sites. Our study shows that the cis-element fluidity recently illustrated in animals also exists in plants, and that it can be detected without any experimental work in each individual species, using a biophysical transcription factor model. A. thaliana LEAFY ChIP-seq w control, 2 replicates