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The position and complex genomic architecture of plant T-DNA insertions revealed by 4C

ABSTRACT: The integration of T-DNA to plant genomes is widely used for basic research and agriculture. High heterogeneity in the number of integration events per genome, their configuration and impact on genome integrity highlight both, the critical need and great challenge to detect the genomic locations of T-DNA insertions and their associated chromosomal rearrangements. Here we present ‘4SEE’, a circular chromosome conformation capture (4C) based method for robust, rapid and cost-efficient detection of the entire scope T-DNA locations. Moreover, by measuring the chromosomal architecture at plant genome flanking the T-DNA insertions, 4SEE outlines their associated complex chromosomal aberrations. Applying 4SEE to a collection of confirmed T-DNA lines revealed previously unmapped T-DNA insertions and chromosomal rearrangements such as inversions and translocations. Uncovering such events in feasible, robust and cost-effective manners by 4SEE in any plant of interest have implications for accurate annotation and phenotypic characterization of T-DNA insertion mutants and transgene expression in basic science applications as well as for plant biotechnology.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE147542 | GEO | 2020/04/05

REPOSITORIES: GEO

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Project description:Over the last 30 years the soil bacterium Agrobacterium tumefaciens has been the workhorse tool for plant genome engineering. Replacement of native tumor-inducing (Ti) plasmid elements with customizable cassettes enabled insertion of a sequence of interest as “Transfer DNA” (T-DNA) into the plant genome of interest. Although these T-DNA transfer mechanisms are well understood, detailed understanding of the structure and epigenomic status of insertion events was limited by current technologies. To fill this gap, we analyzed transgenic Arabidopsis thaliana lines from three widely used collections (SALK, SAIL and WISC) with two single molecule technologies, optical genome mapping and nanopore sequencing. Optical maps for four randomly selected T-DNA lines revealed between one and seven insertions/rearrangements with unexpectedly large sizes ranging from 27 to 236 kilobases. De novo nanopore-based genome assemblies for two heterozygous lines resolved T-DNA structures up to 36 kb and revealed large-scale T-DNA associated translocations and exchange of chromosome arm ends. The multiple internally rearranged nature of T-DNA arrays, consisting of identical T-DNA/backbone concatemers made full assembly even for long nanopore reads impossible. For the current TAIR10 reference genome, nanopore contigs corrected 83% of non-centromeric misassemblies. This unprecedented nucleotide-level definition of T-DNA insertions enabled the mapping of epigenome data. The SALK_059379 T-DNA insertions were enriched for 24nt siRNAs and contained dense cytosine DNA methylation. Transgene silencing via the RNA directed DNA methylation pathway was confirmed by in planta assays. In contrast, SAIL_232 T-DNA sequence was predominantly targeted by 21/22nt siRNAs, and DNA methylation and silencing was limited to the GUS gene, but not the resistance gene. With the emergence of genome editing technologies that rely on Agrobacterium for gene delivery, this study provides new insights into the structural impact of engineering plant genomes and demonstrates the utility of state-of-the-art long-range sequencing technologies to rapidly identify unanticipated genomic changes.

Project description:Transcription factors direct gene expression, and so there is much interest in mapping their genome-wide binding locations. M-BM- Current methods do not allow for the multiplexed analysis of TF binding, and this limits their throughput. We describe a novel method for determining the genomic target genes of multiple transcription factors simultaneously. DNA-binding proteins are endowed with the ability to direct transposon insertions into the genome near to where they bind. The transposon becomes a M-bM-^@M-^\Calling CardM-bM-^@M-^] marking the visit of the DNA-binding protein to that location. A unique sequence M-bM-^@M-^\barcodeM-bM-^@M-^] in the transposon matches it to the DNA-binding protein that directed its insertion. The sequences of the DNA flanking the transposon (which reveal where in the genome the transposon landed) and the barcode within the transposon (which identifies the TF that put it there) are determined by massively-parallel DNA sequencing. To demonstrate the methodM-bM-^@M-^Ys feasibility, we determined the genomic targets of eight transcription factors in a single experiment. The Calling Card method promises to significantly reduce the cost and labor needed to determine the genomic targets of many transcription factors in different environmental conditions and genetic backgrounds. These data contain Ty5 insertion sites mapped by an Illumina GAII analyzer in the S. cerevisiae genome for the background strain without any Sir4 present (1 run), in strains expressing Sir4-tagged copies of three well-characterized TFs: Gal4, Leu3, and Gcn4 (1 run each), and a multiplex of eight Sir4-tagged TFs pooled in a single experiment (2 biological replicates), and insertions from the Thi2-Sir4 fusion expressed from its native locus in two conditions (1 run each). The format of each insertions file is [chromosome number] [position of genomic base] [direction of insertion] [number of reads at that position]. Raw sequencing data comes in two varieties. Paired-end data contains a 5 bp barcode at the beginning of read #2. Single-end data contains a 2 bp barcode on the beggining of read #1.

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The position and complex genomic architecture of plant T-DNA insertions revealed by 4C

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