Project description:In order to pinpoint the most differentially expressed genes between Eucalyptus grandis leaf blades and vascular (xylem) tissues as well as between E. grandis and Eucalyptus globulus xylem tissues, a total number of nine 50mer-oligoprobes covering the length of each one of 21,432 unique sequences derived from the Genolyptus EST dataset were synthesized “on-chip” in duplicate, randomly distributed in two blocks of each slide. Probes were also synthesized from ten cDNA sequences encoding known human proteins as negative controls, totaling 21,442 sequences. Leaves and xylem samples were taken from two E. grandis clonal trees, i.e., both derived from the same matrix tree and harboring the same genotype. Two additional xylem samples were collected from two other E. grandis clonal trees of a different genotype, as well as from two E. globulus clonal trees. Therefore, ten cDNA samples and ten identical chips were produced at Roche NimbleGen for the microarray assays, with a total number of 385,956 features per slide. Besides the discovery of differentially expressed genes between leaf and xylem, we wanted to test the validity of the assumed “technical” and “biological duplicates” since all trees were field-grown and four years-old in age. A ten chip study using total RNA recovered from mature leaf and vascular (xylem) tissues of Eucalyptus grandis and xylem from Eucalyptus globulus trees. Two clonal trees of E. grandis (E.grandis_Clone A_Ramet 1 and E.grandis_Clone A_Ramet 2), derived from a single matrix tree and therefore genomically identical, were the source of two samples of leaf RNA and two samples of xylem RNA, individually hybridized to four chips after cDNA synthesis/Cy3 labeling. Two other clonal trees of E. grandis (E.grandis_Clone B_Ramet 1 and E.grandis_Clone B_Ramet 2), derived from a different matrix tree, were the source of two additional samples of xylem RNA individually hybridized to four chips after cDNA synthesis/Cy3 labeling. Likewise, two pairs of clonal trees of E. globulus (E.globulus_Clone A_Ramet 1 and E.globulus_Clone A_Ramet 2/ E.globulus_Clone B_Ramet 1 and E.globulus_Clone B_Ramet 2), derived from two distinct matrix trees, were the source of four additional samples of xylem RNA, individually hybridized to four chips after cDNA synthesis/Cy3 labeling. Each chip measures the expression level of 21,432 genes from Eucalyptus sp. and ten human genes (negative controls) with nine 50-mer probe pairs (PM/MM) per gene in two separate blocks per chip (technical duplicate), totalizing 18 hybridization signal values per gene per chip.

Project description:Histone modifications play an integral role in plant development, but have been poorly studied in woody plants. Investigating chromatin organization in wood-forming tissue and its role in regulating gene expression allows us to understand the mechanisms underlying cellular differentiation during xylogenesis (wood formation) and identify novel functional regions in plant genomes. However, woody tissue poses unique challenges for using high-throughput chromatin immunoprecipitation (ChIP) techniques for studying genome-wide histone modifications in vivo. We investigated the role of the modified histone H3K4me3 (trimethylated lysine 4 of histone H3) in gene expression during the early stages of wood formation using ChIP-seq in Eucalyptus grandis, a woody biomass model. Plant chromatin fixation and isolation protocols were optimized for developing xylem tissue collected from field-grown E. grandis trees. A “nano-ChIP-seq” procedure was employed for ChIP DNA amplification. Over 9 million H3K4me3 ChIP-seq and 18 million control paired-end reads were mapped to the E. grandis reference genome for peak-calling using Model-based Analysis of ChIP-Seq. The 12,177 significant H3K4me3 peaks identified covered ~1.5% of the genome and overlapped some 9,623 protein-coding genes and 38 noncoding RNAs. H3K4me3 library coverage, peaking ~600 - 700 bp downstream of the transcription start site, was highly correlated with gene expression levels measured with RNA-seq. Overall, H3K4me3-enriched genes tended to be less tissue-specific than unenriched genes and were overrepresented for general cellular metabolism and development gene ontology terms. Relative expression of H3K4me3-enriched genes in developing secondary xylem was higher than unenriched genes, however, and highly expressed secondary cell wall-related genes were enriched for H3K4me3 as validated using ChIP-qPCR. In this first genome-wide analysis of a modified histone in a woody tissue, we developed optimized a ChIP-seq procedure suitable for field-collected samples. In developing E. grandis xylem, H3K4me3 enrichment is an indicator of active transcription, consistent with its known role in sustaining pre-initiation complex formation in yeast. The H3K4me3 ChIP-seq data from this study paves the way to understanding the chromatin landscape and epigenomic architecture of xylogenesis in plants, and complements RNA-seq evidence of gene expression for the future improvement of the E. grandis genome annotation. Examination of H3K4me3 in developing secondary xylem tissue from two clonal individuals of E. grandis growing in the field

Project description:Histone modifications play an integral role in plant development, but have been poorly studied in woody plants. Investigating chromatin organization in wood-forming tissue and its role in regulating gene expression allows us to understand the mechanisms underlying cellular differentiation during xylogenesis (wood formation) and identify novel functional regions in plant genomes. However, woody tissue poses unique challenges for using high-throughput chromatin immunoprecipitation (ChIP) techniques for studying genome-wide histone modifications in vivo. We investigated the role of the modified histone H3K4me3 (trimethylated lysine 4 of histone H3) in gene expression during the early stages of wood formation using ChIP-seq in Eucalyptus grandis, a woody biomass model. Plant chromatin fixation and isolation protocols were optimized for developing xylem tissue collected from field-grown E. grandis trees. A “nano-ChIP-seq” procedure was employed for ChIP DNA amplification. Over 9 million H3K4me3 ChIP-seq and 18 million control paired-end reads were mapped to the E. grandis reference genome for peak-calling using Model-based Analysis of ChIP-Seq. The 12,177 significant H3K4me3 peaks identified covered ~1.5% of the genome and overlapped some 9,623 protein-coding genes and 38 noncoding RNAs. H3K4me3 library coverage, peaking ~600 - 700 bp downstream of the transcription start site, was highly correlated with gene expression levels measured with RNA-seq. Overall, H3K4me3-enriched genes tended to be less tissue-specific than unenriched genes and were overrepresented for general cellular metabolism and development gene ontology terms. Relative expression of H3K4me3-enriched genes in developing secondary xylem was higher than unenriched genes, however, and highly expressed secondary cell wall-related genes were enriched for H3K4me3 as validated using ChIP-qPCR. In this first genome-wide analysis of a modified histone in a woody tissue, we developed optimized a ChIP-seq procedure suitable for field-collected samples. In developing E. grandis xylem, H3K4me3 enrichment is an indicator of active transcription, consistent with its known role in sustaining pre-initiation complex formation in yeast. The H3K4me3 ChIP-seq data from this study paves the way to understanding the chromatin landscape and epigenomic architecture of xylogenesis in plants, and complements RNA-seq evidence of gene expression for the future improvement of the E. grandis genome annotation.

Dataset Information

Genolyptus microarray studies of Eucalyptus grandis and Eucalyptus globulus leaf and xylem tissues

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