Photoperiod-responsive changes in chromatin accessibility in phloem companion and epidermis cells of Arabidopsis leaves.

Photoperiod plays a key role in controlling the phase transition from vegetative to reproductive growth in flowering plants. Leaves are the major organs perceiving day-length signals, but how specific leaf cell types respond to photoperiod remains unknown. We integrated photoperiod-responsive chromatin accessibility and transcriptome data in leaf epidermis and vascular companion cells of Arabidopsis thaliana by combining isolation of nuclei tagged in specific cell/tissue types with assay for transposase-accessible chromatin using sequencing and RNA-sequencing. Despite a large overlap, vasculature and epidermis cells responded differently. Long-day predominantly induced accessible chromatin regions (ACRs); in the vasculature, more ACRs were induced and these were located at more distal gene regions, compared with the epidermis. Vascular ACRs induced by long days were highly enriched in binding sites for flowering-related transcription factors. Among the highly ranked genes (based on chromatin and expression signatures in the vasculature), we identified TREHALOSE-PHOSPHATASE/SYNTHASE 9 (TPS9) as a flowering activator, as shown by the late flowering phenotypes of T-DNA insertion mutants and transgenic lines with phloem-specific knockdown of TPS9. Our cell-type-specific analysis sheds light on how the long-day photoperiod stimulus impacts chromatin accessibility in a tissue-specific manner to regulate plant development.

De novo transcriptome assembly of the oak processionary moth Thaumetopoea processionea.

OBJECTIVES: The oak processionary moth (OPM) (Thaumetopoea processionea) is a species of moth (order: Lepidoptera) native to parts of central Europe. However, in recent years, it has become an invasive species in various countries, particularly in the United Kingdom and the Netherlands. The larvae of the OPM are covered with urticating barbed hairs (setae) causing irritating and allergic reactions at the three last larval stages (L3-L5). The aim of our study was to generate a de novo transcriptomic assembly for OPM larvae by including one non-allergenic stage (L2) and two allergenic stages (L4 and L5). A transcriptomic assembly will help identify potential allergenic peptides produced by OPM larvae, providing valuable information for developing novel therapeutic strategies and allergic immunodiagnostic assays. DATA: Transcriptomes of three larval stages of the OPM were de novo assembled and annotated using Trinity and Trinotate, respectively. A total of 145,251 transcripts from 99,868 genes were identified. Bench-marking universal single-copy orthologues analysis indicated high completeness of the assembly. About 19,600 genes are differentially expressed between the non-allergenic and allergenic larval stages. The data provided here contribute to the characterization of OPM, which is both an invasive species and a health hazard.

A two-step adaptive walk rewires nutrient transport in a challenging edaphic environment.

Most well-characterized cases of adaptation involve single genetic loci. Theory suggests that multilocus adaptive walks should be common, but these are challenging to identify in natural populations. Here, we combine trait mapping with population genetic modeling to show that a two-step process rewired nutrient homeostasis in a population of Arabidopsis as it colonized the base of an active stratovolcano characterized by extremely low soil manganese (Mn). First, a variant that disrupted the primary iron (Fe) uptake transporter gene (IRT1) swept quickly to fixation in a hard selective sweep, increasing Mn but limiting Fe in the leaves. Second, multiple independent tandem duplications occurred at NRAMP1 and together rose to near fixation in the island population, compensating the loss of IRT1 by improving Fe homeostasis. This study provides a clear case of a multilocus adaptive walk and reveals how genetic variants reshaped a phenotype and spread over space and time.

Targeted DNA methylation represses two enhancers of FLOWERING LOCUS T in Arabidopsis thaliana.

FLOWERING LOCUS T (FT) plays a major role in regulating the floral transition in response to an inductive long day photoperiod in Arabidopsis thaliana. Expression of FT in leaves is dependent on the distal transcriptional enhancer Block C, located 5-kilobases (kb) upstream of the transcriptional start site (TSS). We expressed an inverted repeat of Block C to induce local DNA methylation and heterochromatin formation, which lead to FT downregulation in an inductive photoperiod. Using targeted DNA methylation as a tool to uncover further regulatory regions at the FT locus, we identified Block E, located 1 kb downstream of the gene, as a novel enhancer of FT. As Block C, Block E is conserved across Brassicaceae and located in accessible chromatin. Block C and E act as additive transcriptional enhancers that, in combination with the proximal FT promoter, control expression of FT in response to photoperiod in the leaf phloem.

Genome-wide mapping of transcriptional enhancer candidates using DNA and chromatin features in maize.

BACKGROUND: While most cells in multicellular organisms carry the same genetic information, in each cell type only a subset of genes is being transcribed. Such differentiation in gene expression depends, for a large part, on the activation and repression of regulatory sequences, including transcriptional enhancers. Transcriptional enhancers can be located tens of kilobases from their target genes, but display characteristic chromatin and DNA features, allowing their identification by genome-wide profiling. Here we show that integration of chromatin characteristics can be applied to predict distal enhancer candidates in Zea mays, thereby providing a basis for a better understanding of gene regulation in this important crop plant. RESULT: To predict transcriptional enhancers in the crop plant maize (Zea mays L. ssp. mays), we integrated available genome-wide DNA methylation data with newly generated maps for chromatin accessibility and histone 3 lysine 9 acetylation (H3K9ac) enrichment in young seedling and husk tissue. Approximately 1500 intergenic regions, displaying low DNA methylation, high chromatin accessibility and H3K9ac enrichment, were classified as enhancer candidates. Based on their chromatin profiles, candidate sequences can be classified into four subcategories. Tissue-specificity of enhancer candidates is defined based on the tissues in which they are identified and putative target genes are assigned based on tissue-specific expression patterns of flanking genes. CONCLUSIONS: Our method identifies three previously identified distal enhancers in maize, validating the new set of enhancer candidates and enlarging the toolbox for the functional characterization of gene regulation in the highly repetitive maize genome.

Plant Enhancers: A Call for Discovery.

Higher eukaryotes typically contain many different cell types, displaying different cellular functions that are influenced by biotic and abiotic cues. The different functions are characterized by specific gene expression patterns mediated by regulatory sequences such as transcriptional enhancers. Recent genome-wide approaches have identified thousands of enhancers in animals, reviving interest in enhancers in gene regulation. Although the regulatory roles of plant enhancers are as crucial as those in animals, genome-wide approaches have only very recently been applied to plants. Here we review characteristics of enhancers at the DNA and chromatin level in plants and other species, their similarities and differences, and techniques widely used for genome-wide discovery of enhancers in animal systems that can be implemented in plants.

Chromatin and epigenetics in all their states: Meeting report of the first conference on Epigenetic and Chromatin Regulation of Plant Traits - January 14 - 15, 2016 - Strasbourg, France.

In January 2016, the first Epigenetic and Chromatin Regulation of Plant Traits conference was held in Strasbourg, France. An all-star lineup of speakers, a packed audience of 130 participants from over 20 countries, and a friendly scientific atmosphere contributed to make this conference a meeting to remember. In this article we summarize some of the new insights into chromatin, epigenetics, and epigenomics research and highlight nascent ideas and emerging concepts in this exciting area of research.