A survey of genome-wide single nucleotide polymorphisms through genome resequencing in the Périgord black truffle (Tuber melanosporum Vittad.)

Abstract

The Périgord black truffle (Tuber melanosporum Vittad.), considered a gastronomic delicacy worldwide, is an ectomycorrhizal filamentous fungus that is ecologically important in Mediterranean French, Italian and Spanish woodlands. In this study, we developed a novel resource of single nucleotide polymorphisms (SNPs) for T. melanosporum using Illumina high-throughput resequencing. The genome from six T. melanosporum geographical accessions was sequenced to a depth of approximately 20×. These geographical accessions were selected from different populations within the northern and southern regions of the geographical species distribution. Approximately 80% of the reads for each of the six resequenced geographical accessions mapped against the reference T. melanosporum genome assembly, estimating the core genome size of this organism to be approximately 110 Mbp. A total of 442 326 SNPs corresponding to 3540 SNPs/Mbps were identified as being included in all seven genomes. The SNPs occurred more frequently in repeated sequences (85%), although 4501 SNPs were also identified in the coding regions of 2587 genes. Using the ratio of nonsynonymous mutations per nonsynonymous site (pN) to synonymous mutations per synonymous site (pS) and Tajima's D index scanning the whole genome, we were able to identify genomic regions and genes potentially subjected to positive or purifying selection. The SNPs identified represent a valuable resource for future population genetics and genomics studies.

Keywords: SNP resource; black truffle; genome resequencing; next-generation sequencing.