Genome-wide genotyping and SNP discovery by ultra-deep Restriction-Associated DNA (RAD) tag sequencing of pooled samples of E. grandis and E. globulus

Abstract

The availability of next generation sequencing (NGS) technologies has opened the door to new strategies of SNP discovery and genotyping. Rapid genome-wide SNP detection via deep resequencing of reduced representation libraries of restriction digested pools of genomic DNA combined with a reference genome has been successfully used for SNP discovery in microorganisms [1], plants [2]and domestic animals [3]. Taking a step further from using NGS for SNP discovery, Baird et al [1]showed that NGS of short tags derived from barcoded multiplexed genomic representations generated with restriction enzymes could be used for direct genotyping of individuals, calling this method RAD (Restriction-site associated DNA) sequencing. RAD sequencing involves cutting a genome with at least one restriction enzyme and NGS the ends of the resulting fragments. We have recently developed a first set of SNPs for high-throughput genotyping of species of Eucalyptus. Although SNP assay success was high, the proportion of polymorphic SNPs declined as phylogenetic distance between species increased, down to <20% when contrasting E. grandis and E. globulus, the two main worldwide commercially planted species were considered [4]. In this work we used RAD sequencing to discover polymorphic SNPs across these two species. Additionally we were interested in assessing the potential of RAD for direct genotyping-by-sequencing in Eucalyptus.