Project description:Phenotype-driven forward genetic experiments are among the most powerful approaches for linking biology and disease to genomic elements. Although widely used in a range of model organisms, positional cloning of causal variants is still a very laborious process. Here, we describe a novel universal approach, named fast forward genetics that combines traditional bulk segregant techniques with next-generation sequencing technology and targeted genomic enrichment, to dramatically improve the process of mapping and cloning multiple mutants in a single experiment. In a two-step procedure the mutation is first roughly mapped by ‘light’ sequencing of the bulk segregant pool, followed by genomic enrichment and deep-sequencing of the mutant pool for the linked genomic region. The latter step allows for simultaneous fine-mapping and mutation discovery. We successfully applied this approach to three Arabidopsis mutants, but the method can in principle be applied to any model organism of interest and is largely independent of the genome size. Moreover, we show that both steps can be performed in multiplex using barcoded samples, thereby increasing efficiency enormously. Inducible overexpression of the RETINOBLASTOMA-RELATED (RBR-OE) gene in Arabidopsis roots causes the complete differentiation of stem cells and premature differentiation of daughter cells, leading to a full exhaustion of the primary root meristem. In order to identify regulators of RBR function in cell differentiation, RBR-OE plants in the Columbia background (Col0) were treated with EMS mutagenesis and a set of genetic suppressors of RBR-OE, which restores root growth capacity, were isolated. In this study, we used one the identified suppressor lines, which segregated as a recessive mutation. Mapping populations were generated by outcrossing to Ler ecotype. Seedlings from the F2 population were grown for 15 days post germination (dpg). A pool of 60 seedlings each with a clear suppressor phenotype (homozygous for suppressor mutation) and of 60 seedlings showing RBOE phenotype (Heterozygous for the suppressor mutation) were prepared and genomic DNA was isolated with the RNeasy Plant Mini Kit from QIAGEN according to manufacturer's protocol. The other two, mutants 136 and 193 were obtained in fluorescence based mutant screen and a QCmarker based mutagenesis, respectively. Mutants were generated by chemical mutagenesis (EMS) in Colombia (Col) genetic background. Mutants were subsequently crossed to the Landsberg (Ler) ecotype to create the mapping populations. Bulk-segregant pools of about 200 mutant as well as wild-type plants were generated for every mutant line.

Project description:Targeted genomic enrichment followed by next-generation sequencing dramatically increased the efficiency of mutation discovery in human genomes. Here we demonstrate that these techniques also revolutionize traditional genetic approaches in model systems. We developed a two-step protocol utilizing a traditional bulk-segregant analysis (BSA) approach for positional cloning mutants in phenotype-driven forward genetic screens. First, BSA pools are 'light' sequenced for rough mapping, followed by targeted enrichment and deep-sequencing of the mutant BSA pool for the linked genomic region to fine-map and discover candidate mutations. We applied this method successfully to three Arabidopsis mutants and show that it can be scaled by multiplexing. Similarly, we applied these techniques to a gene-driven reverse genetics method (chemical driven target-selected mutagenesis or TILLING) that is used for generating gene knockouts in a wide range of organisms, including plants, invertebrates and vertebrates. We developed an efficient multiplexed genomic enrichment protocol for pre-barcoded samples. As a proof-of-principle, 770 genes were screened for induced mutations in 30 rats, which identified all but one known variants (30) as well as a large series of novel knockout and missense alleles. Mutations were retrieved at the expected frequency with a the false-positive rate of less than 1 in 6 million basepairs, which is much lower as compared to traditional mutation discovery approaches. Both methods are largely independent of the genome size due to the targeted enrichment and can thus be applied to any genetic model system of interest. Targeted genomic enrichment followed by next-generation sequencing dramatically increased the efficiency of mutation discovery in human genomes. Here we demonstrate that these techniques also revolutionize traditional genetic approaches in model systems. We developed a two-step protocol utilizing a traditional bulk-segregant analysis (BSA) approach for positional cloning mutants in phenotype-driven forward genetic screens. First, BSA pools are 'light' sequenced for rough mapping, followed by targeted enrichment and deep-sequencing of the mutant BSA pool for the linked genomic region to fine-map and discover candidate mutations. We applied this method successfully to three Arabidopsis mutants and show that it can be scaled by multiplexing. Similarly, we applied these techniques to a gene-driven reverse genetics method (chemical driven target-selected mutagenesis or TILLING) that is used for generating gene knockouts in a wide range of organisms, including plants, invertebrates and vertebrates. We developed an efficient multiplexed genomic enrichment protocol for pre-barcoded samples. As a proof-of-principle, 770 genes were screened for induced mutations in 30 rats, which identified all but one known variants (30) as well as a large series of novel knockout and missense alleles. Mutations were retrieved at the expected frequency with a the false-positive rate of less than 1 in 6 million basepairs, which is much lower as compared to traditional mutation discovery approaches. Both methods are largely independent of the genome size due to the targeted enrichment and can thus be applied to any genetic model system of interest.

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Arabidopsis thaliana

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