Allan Booth

Exome capture is a reduced representation approach that selectively captures sequence from only the gene-bearing regions of a genome. It is based on probes targeted at these regions and, compared with whole genome shotgun sequencing, leads to a significant reduction in cost and data processing effort while still providing insights into the most relevant part of a genome. An exome capture array for barley was released in 2013 and this has opened the door to numerous studies that have put this technology to good use. In this chapter we detail the laboratory protocols required for enrichment and sequencing, and provide detailed step-by-step instructions for the bioinformatics analysis of the resulting data.

\ud Barley is a model species for the investigation of the evolution, adaptation and spread of the world’s important crops. In this article, we describe the first application of an oligonucleotide pool assay single nucleotide polymorphism (SNP) platform to assess the evolution of barley in a portion of the Fertile Crescent, a key region in the development of farming.\ud \ud •\ud A large collection of > 1000 genetically mapped, genome-wide SNPs was assayed in geographically matched landrace and wild barley accessions (N = 448) from Jordan and Syria.\ud \ud •\ud Landrace and wild barley categories were clearly genetically differentiated, but a limited degree of secondary contact was evident. Significant chromosome-level differences in diversity between barley types were observed around genes known to be involved in the evolution of cultivars. The region of Jordan and southern Syria, compared with the north of Syria, was supported by SNP data as a more likely domestication origin.\ud \ud •\ud Our data provide evidence for hybridization as a possible mechanism for the continued adaptation of landrace barley under cultivation, indicate regions of the genome that may be subject to selection processes and suggest limited origins for the development of the cultivated crop.\u

More than 2,000 genome-wide barley single nucleotide polymorphisms (SNPs) were developed by resequencing unigene fragments from eight diverse accessions. The average genome-wide SNP frequency observed in 877 unigenes was 1 SNP per 200 bp. However, SNP frequency was highly variable with the least number of SNP and SNP haplotypes observed within European cultivated germplasm reflecting effects of breeding history on genetic diversity. More than 300 SNP loci were mapped genetically in three experimental mapping populations which allowed the construction of an integrated SNP map incorporating a large number of RFLP, AFLP and SSR markers (1,237 loci in total). The genes used for SNP discovery were selected based on their transcriptional response to a variety of abiotic stresses. A set of known barley abiotic stress QTL was positioned on the linkage map, while the available sequence and gene expression information facilitated the identification of genes potentially associated with these traits. Comparison of the sequenced SNP loci to the rice genome sequence identified several regions of highly conserved gene order providing a framework for marker saturation in barley genomic regions of interest. The integration of genome-wide SNP and expression data with available genetic and phenotypic information will facilitate the identification of gene function in barley and other non-model organisms.