Chromosome level high-density integrated genetic maps improve the Pyrus bretschneideri 'DangshanSuli' v1.0 genome.

Chromosomal level reference genomes provide a crucial foundation for genomics research such as genome-wide association studies (GWAS) and whole genome selection. The chromosomal-level sequences of both the European (Pyrus communis) and Chinese (P. bretschneideri) pear genomes have not been published in public databases so far. To anchor the scaffolds of P. bretschneideri 'DangshanSuli' (DS) v1.0 genome into pseudo-chromosomes, two genetic maps (MH and YM maps) were constructed using half sibling populations of Chinese pear crosses, 'Mantianhong' (MTH) × 'Hongxiangsu' (HXS) and 'Yuluxiang' (YLX) × MTH, from 345 and 162 seedlings, respectively, which were prepared for SNP discovery using genotyping-by-sequencing (GBS) technology. The MH and YM maps, each with 17 linkage groups (LGs), were constructed from 2606 and 2489 SNP markers and spanned 1847 and 1668 cM, respectively, with average marker intervals of 0.7. The two maps were further merged with a previously published genetic map (BD) based on the cross 'Bayuehong' (BYH) × 'Dangshansuli' (DS) to build a new integrated MH-YM-BD map. By using 7757 markers located on the integrated MH-YM-BD map, 898 scaffolds (400.57 Mb) of the DS v1.0 assembly were successfully anchored into 17 pseudo-chromosomes, accounting for 78.8% of the assembled genome size. About 88.31% of them (793 scaffolds) were directionally anchored with two or more markers on the pseudo-chromosomes. Furthermore, the errors in each pseudo-chromosome (especially 1, 5, 7 and 11) were manually corrected and pseudo-chromosomes 1, 5 and 7 were extended by adding 19, 12 and 14 scaffolds respectively in the newly constructed DS v1.1 genome. Synteny analyses revealed that the DS v1.1 genome had high collinearity with the apple genome, and the homologous fragments between pseudo-chromosomes were similar to those found in previous studies. Moreover, the red-skin trait of Asian pear was mapped to an identical locus as identified previously. The accuracy of DS v1.1 genome was improved by using larger mapping populations and merged genetic map. With more than 400 MB anchored to 17 pseudo-chromosomes, the new DS v1.1 genome provides a critical tool that is essential for studies of pear genetics, genomics and molecular breeding.

Xue H ，Wang S ，Yao JL ，Deng CH ，Wang L ，Su Y ，Zhang H ，Zhou H ，Sun M ，Li X ，Yang J ... -  《BMC GENOMICS》

Integrated high-density consensus genetic map of Pyrus and anchoring of the 'Bartlett' v1.0 (Pyrus communis) genome.

Genetic maps are essential tools for pear genetics and genomics research. In this study, we first constructed an integrated simple sequence repeat (SSR) and single nucleotide polymorphism (SNP)-based consensus genetic map for pear based on common SSR markers between nine published maps. A total of 5,085 markers, including 1,232 SSRs and 3,853 SNPs, were localized on a consensus map spanning 3,266.0 cM in total, with an average marker interval of 0.64 cM, which represents the highest density consensus map of pear to date. Using three sets of high-density SNP-based genetic maps with European pear genetic backgrounds, we anchored a total of 291.5 Mb of the 'Bartlett' v1.0 (Pyrus communis L.) genome scaffolds into 17 pseudo-chromosomes. This accounted for 50.5% of the genome assembly, which was a great improvement on the 29.7% achieved originally. Intra-genome and inter-genome synteny analyses of the new 'Bartlett' v1.1 genome assembly with the Asian pear 'Dangshansuli' (Pyrus bretschneideri Rehd.) and apple (Malus × domestica Borkh.) genomes uncovered four new segmental duplication regions. The integrated high-density SSR and SNP-based consensus genetic map provided new insights into the genetic structure patterns of pear and assisted in the genome assembly of 'Bartlett' through further exploration of different pear genetic maps.

Li L ，Deng CH ，Knäbel M ，Chagné D ，Kumar S ，Sun J ，Zhang S ，Wu J ... -  《-》

High-resolution genetic linkage map of European pear (Pyrus communis) and QTL fine-mapping of vegetative budbreak time.

Gabay G ，Dahan Y ，Izhaki Y ，Faigenboim A ，Ben-Ari G ，Elkind Y ，Flaishman MA ... -  《BMC PLANT BIOLOGY》

Exploiting genotyping by sequencing to characterize the genomic structure of the American cranberry through high-density linkage mapping.

Covarrubias-Pazaran G ，Diaz-Garcia L ，Schlautman B ，Deutsch J ，Salazar W ，Hernandez-Ochoa M ，Grygleski E ，Steffan S ，Iorizzo M ，Polashock J ，Vorsa N ，Zalapa J ... -  《BMC GENOMICS》

Genome-wide characterization of simple sequence repeats in Pyrus bretschneideri and their application in an analysis of genetic diversity in pear.

Xue H ，Zhang P ，Shi T ，Yang J ，Wang L ，Wang S ，Su Y ，Zhang H ，Qiao Y ，Li X ... -  《BMC GENOMICS》