A high-density, multi-parental SNP genetic map on apple validates a new mapping approach for outcrossing species

Quantitative trait loci(QTL)mapping approaches rely on the correct ordering of molecular markers along the chromosomes,which can be obtained from genetic linkage maps or a reference genome sequence.For apple(Malus domestica Borkh),the genome sequence v1 and v2 could not meet this need;therefore,a novel approach was devised to develop a dense genetic linkage map,providing the most reliable marker-loci order for the highest possible number of markers.The approach was based on four strategies:(i)the use of multiple full-sib families,(ii)the reduction of missing information through the use of HaploBlocks and alternative calling procedures for single-nucleotide polymorphism(SNP)markers,(iii)the construction of a single backcross-type data set including all families,and(iv)a two-step map generation procedure based on the sequential inclusion of markers.The map comprises 15417 SNP markers,clustered in 3 K HaploBlock markers spanning 1267 cM,with an average distance between adjacent markers of 0.37 cM and a maximum distance of 3.29 cM.Moreover,chromosome 5 was oriented according to its homoeologous chromosome 10.This map was useful to improve the apple genome sequence,design the Axiom Apple 480 K SNP array and perform multifamily-based QTL studies.Its collinearity with the genome sequences v1 and v3 are reported.To our knowledge,this is the shortest published SNP map in apple,while including the largest number of markers,families and individuals.This result validates our methodology,proving its value for the construction of integrated linkage maps for any outbreeding species.

Genomic signatures of different adaptations to environmental stimuli between wild and cultivated Vitis vinifera L

The application of population genetic methods in combination with gene mapping strategies can help to identify genes and mutations selected during the evolution from wild plants to crops and to explore the considerable genetic variation still maintained in natural populations.We genotyped a grapevine germplasm collection of 44 wild(Vitis vinifera subsp.sylvestris)and 48 cultivated(V.vinifera subsp.sativa)accessions at 54 K single-nucleotide polymorphisms(SNPs)to perform a whole-genome comparison of the main population genetic statistics.The analysis of Wright Fixation Index(FST)along the whole genome allowed us to identify several putative“signatures of selection”spanning over two thousand SNPs significantly differentiated between sativa and sylvestris.Many of these genomic regions included genes involved in the adaptation to environmental changes.An overall reduction of nucleotide diversity was observed across the whole genome within sylvestris,supporting a small effective population size of the wild grapevine.Tajima’s D resulted positive in both wild and cultivated subgroups,which may indicate an ongoing balancing selection.Association mapping for six domestication-related traits was performed in combination with population genetics,providing further evidence of different perception and response to environmental stresses between sativa and sylvestris.