Project description:Although the pattern of lateral organ formation from apical meristems establishes species-specific plant architecture, the positional information that confers cell fate to cells as they transit to the meristem flanks where they differentiate, remains largely unknown. We have combined fluorescence-activated cell sorting and RNA-seq to characterise the cell-type-specific transcriptome at the earliest developmental time-point of lateral organ formation using DORNRÖSCHEN-LIKE::GFP to mark founder-cell populations at the periphery of the inflorescence meristem (IM) in apetala1 cauliflower double mutants, which overproliferate IMs. Within these founder-cells, floral primordium identity genes are upregulated and stem-cell identity markers are downregulated. The transcriptional network of differentially expressed genes supports the hypothesis that lateral organ founder-cell specification involves the creation of polarity from the centre to the periphery of the IM and the establishment of a boundary from surrounding cells, consistent with bract initiation. In contrast to the established paradigm that sites of auxin response maxima pre-pattern lateral organ initiation in the IM, only subtle transcriptional reprogramming within the global auxin network was observed, suggesting that auxin response might play a minor role in the earliest stages of lateral floral initiation.
Project description:Two methods Fluorescence Activated Cell Sorting (FACS) and Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-seq) are combined to analyse the chromatin accessibility of Lateral Organ Founder Cells (LOFCs) in the peripheral zone of the apetala1 cauliflower double mutant Arabidopsis inflorescence meristem. Genome-wide we observed a striking correlation between Transposase Hypersensitive Sites (THS) detected in ATAC-seq and DNase I Hypersensitive Sites (DHS), covering mostly extended regions substructured into several individual THS that correspond to phylogenetically conserved sequence, enhancer elements and binding sites of MADS-box transcription factors. Relative to available RNA-seq data, chromatin configuration changes according to gene activation or repression, i.e. at cellular resolution chromatin regions gain or lose Tn5 transposase accessibility in direct correlation with gene expression levels. A pronounced THS priority immediately upstream of the transcription start and reduced numbers of THSs in the transcription unit are complementary to established H3K4me3 activation or H3K27me3 repressive marks. At this resolution, the FACS/ATAC-seq combination should be widely applicable to detect chromatin changes in course of cell type specification and facilitate the detection of regulatory promoter elements in plant promoters.
Project description:Description of gene expression in various types of cauliflower (including Romanesco type) Cauliflower structures develop on inflorescences from plants such as the apetala1 cauliflower double mutant in Arabidopsis thaliana or in the edible Brassica oleracea var botrytis or Romanesco. Whereas the genetic basis for the development of such structure is well understood in the model plant Arabidopsis thaliana, it is less understood in Brassica oleracea. In order to gain insight into the gene expression present in cauliflower and Romanesco curds, we performed RNA-seq analyses of mature cauliflowers and Romanesco curds and from growing cauliflowers curds. This analysis allowed to establish the nature of genes from the APETALA1 and CAULIFLOWER clade that are either mutated or expressed at very low levels in curd structures. These results shed light on the molecular nature of structures that have been selected in the domestication process.
Project description:Plant inflorescence-to-floral phase transition is an important developmental stage, in which floral cell identities and many traits of reproductive organs are determined. Two MADS-domain transcription factors, APETALA1 (AP1) and CAULIFLOWER (CAL), have been known as master regulators controlling the early stage of the phase transition in Arabidopsis. In plants with loss-of-function alleles of ap1 and cal double mutations, flower development is heavily delayed at the flower initiation stage and accumulate a large number of inflorescence-like meristem cells compared to wild-type plants, resulting in a cauliflower-like phenotype. To facilitate investigation on molecular mechanisms during inflorescence-to-floral phase transition, an inducible system of synchronized floral development has been developed, in which ap1,cal inflorescence-like meristem cells express a fusion protein of AP1 and the hormone-binding domain of the rat glucocorticoid receptor (GR) driven by 35S constitutive promoter. When inflorescences of 35S:AP1-GR ap1,cal plants are treated by steroid hormone dexamethasone as the activator to allow the AP1-GR fusion protein translocate into nucleus, inflorescence-to-floral phase transition is triggered and plants start to produce hundreds of relatively synchronized floral buds. To explore molecular basis at early stage of flower development in Arabidopsis, we used the inducible system of synchronized floral development (35S:AP1-GR ap1,cal) to profile transcriptome change of meristem cells during inflorescence-to-floral phase transition by strand-specific RNA-sequencing.
Project description:The APETALA2 (AP2) transcription factor regulates flower development, floral transition and shoot apical meristem (SAM) maintenance in Arabidopsis. AP2 is also regulated at the post-transcriptional level by microRNA172 (miR172), but the contribution of this to SAM maintenance is poorly understood. We generated transgenic plants carrying a form of AP2 that is resistant to miR172 (rAP2) or carrying a wild-type AP2 susceptible to miR172. Phenotypic and genetic analyses were performed on these lines and mir172 mutants to study the role of AP2 regulation by miR172 on meristem size and the rate of flower production. We found that rAP2 enlarges the inflorescence meristem by increasing cell size and cell number. Misexpression of rAP2 from heterologous promoters showed that AP2 acts in the central zone (CZ) and organizing center (OC) to increase SAM size. Furthermore, we found that AP2 is negatively regulated by AUXIN RESPONSE FACTOR 3 (ARF3). However, genetic analyses indicated that ARF3 also influences SAM size and flower production rate independently of AP2. The study identifies miR172/AP2 as a regulatory module controlling inflorescence meristem size and suggests that transcriptional regulation of AP2 by ARF3 fine tunes SAM size determination.
Project description:Small RNA sequences from Arabidopsis thaliana Col-0 inflorescence tissues of three biological replicates. The data were analyzed to identify non-templated nucleotides in Arabidopsis small RNAs.
Project description:We report the application of laser capture microdissection (LCM) for high resolution transcriptome profiling of the second internode of the Arabidopsis thaliana inflorescence stem. In this series, we used LCM to determine and compare the transcriptome profiles of the phloem cap, the pith, and the remaining vascular bundle area.