Chromosome Level Assembly of Homozygous Inbred Line 'Wongyo 3115' Facilitates the Construction of a High-Density Linkage Map and Identification of QTLs Associated With Fruit Firmness in Octoploid Strawberry (Fragaria × ananassa)

Hye-Eun Lee; Abinaya Manivannan; Sun Yi Lee; Koeun Han; Jun-Geol Yeum; Jinkwan Jo; Jinhee Kim; Il Rae Rho; Ye-Rin Lee; Eun Su Lee; Byoung-Cheorl Kang; Do-Sun Kim

doi:10.3389/fpls.2021.696229

Chromosome Level Assembly of Homozygous Inbred Line 'Wongyo 3115' Facilitates the Construction of a High-Density Linkage Map and Identification of QTLs Associated With Fruit Firmness in Octoploid Strawberry (Fragaria × ananassa)

Front Plant Sci. 2021 Jul 14:12:696229. doi: 10.3389/fpls.2021.696229. eCollection 2021.

Authors

Affiliations

¹ Vegetable Research Division, National Institute of Horticultural and Herbal Science, Rural Development Administration, Jeonju, South Korea.
² Department of Agriculture, Forestry and Bioresources, Plant Genomics and Breeding Institute, College of Agriculture and Life Sciences, Seoul National University, Seoul, South Korea.
³ Department of Agronomy, Institute of Agriculture and Life Sciences, Gyeongsang National University, Jinju, South Korea.

Abstract

Strawberry is an allo-octoploid crop with high genome heterozygosity and complexity, which hinders the sequencing and the assembly of the genome. However, in the present study, we have generated a chromosome level assembly of octoploid strawberry sourced from a highly homozygous inbred line 'Wongyo 3115', using long- and short-read sequencing technologies. The assembly of 'Wongyo 3115' produced 805.6 Mb of the genome with 323 contigs scaffolded into 208 scaffolds with an N50 of 27.3 Mb after further gap filling. The whole genome annotation resulted in 151,892 genes with a gene density of 188.52 (genes/Mb) and validation of a genome, using BUSCO analysis resulted in 94.10% complete BUSCOs. Firmness is one of the vital traits in strawberry, which facilitate the postharvest shelf-life qualities. The molecular and genetic mechanisms that contribute the firmness in strawberry remain unclear. We have constructed a high-density genetic map based on the 'Wongyo 3115' reference genome to identify loci associated with firmness in the present study. For the quantitative trait locus (QTL) identification, the 'BS F₂' populations developed from two inbred lines were genotyped, using an Axiom 35K strawberry chip, and marker positions were analyzed based on the 'Wongyo 3115' genome. Genetic maps were constructed with 1,049 bin markers, spanning the 3,861 cM. Using firmness data of 'BS F₂' obtained from 2 consecutive years, five QTLs were identified on chromosomes 3-3, 5-1, 6-1, and 6-4. Furthermore, we predicted the candidate genes associated with firmness in strawberries by utilizing transcriptome data and QTL information. Overall, we present the chromosome-level assembly and annotation of a homozygous octoploid strawberry inbred line and a linkage map constructed to identify QTLs associated with fruit firmness.

Keywords: QTL analysis; de novo assembly; firmness; high density genetic map; homozygous inbred line.