Construction of chromosome segment substitution lines enables QTL mapping for flowering and morphological traits in Brassica rapa.

Xiaonan Li,Kangning Li,Yong Pyo Lim,Zhe Wang,Wenke Wang,Zhongyun Piao

doi:10.3389/fpls.2015.00432

Abstract

Chromosome segment substitution lines (CSSLs) represent a powerful method for precise quantitative trait loci (QTL) detection of complex agronomical traits in plants. In this study, we used a marker-assisted backcrossing strategy to develop a population consisting of 63 CSSLs, derived from backcrossing of the F1 generated from a cross between two Brassica rapa subspecies: “Chiifu” (ssp. pekinensis), the Brassica “A” genome-represented line used as the donor, and “49caixin” (ssp. parachinensis), a non-heading cultivar used as the recipient. The 63 CSSLs covered 87.95% of the B. rapa genome. Among them, 39 lines carried a single segment; 15 lines, two segments; and nine lines, three or more segments of the donor parent chromosomes. To verify the potential advantage of these CSSL lines, we used them to locate QTL for six morphology-related traits. A total of 58 QTL were located on eight chromosomes for all six traits: 17 for flowering time, 14 each for bolting time and plant height, six for plant diameter, two for leaf width, and five for flowering stalk diameter. Co-localized QTL were mainly distributed on eight genomic regions in A01, A02, A05, A06, A08, A09, and A10, present in the corresponding CSSLs. Moreover, new chromosomal fragments that harbored QTL were identified using the findings of previous studies. The CSSL population constructed in our study paves the way for fine mapping and cloning of candidate genes involved in late bolting, flowering, and plant architecture-related traits in B. rapa. Furthermore, it has great potential for future marker-aided gene/QTL pyramiding of other interesting traits in B. rapa breeding.

Highlights

Segregating populations have been widely used in genetic mapping, quantitative trait loci (QTL) analysis, and gene discovery
chromosome segment substitution lines (CSSLs) Population Development and markerassisted selection (MAS) A framework map was constructed on the basis of the BC1F1 generation by using the 110 genome-wide distributed simple sequence repeat (SSR) markers
In B. rapa, numerous QTL-mapping studies have been conducted for identifying agronomical traits (Ge et al, 2011b; Li et al, 2013), quality traits (Lou et al, 2008; Zhao et al, 2008), and disease resistance traits (Piao et al, 2009; Chen et al, 2013), very few have been used for the genetic improvement of varieties in plant breeding programs

Summary

Introduction

Segregating populations have been widely used in genetic mapping, quantitative trait loci (QTL) analysis, and gene discovery. Advanced mapping populations, including chromosome segment substitution lines (CSSLs), recombinant chromosome substitution lines (RCSLs), introgression lines (ILs), backcross inbred lines (BILs), and near-isogenic lines (NILs), allow to achieve precise QTL identification. These mapping populations have been used for many species such as rice (Ebitani et al, 2005; Tian et al, 2006; Gu et al, 2012), tomato (Eshed and Zamir, 1995; Monforte and Tanksley, 2000), lettuce (Jeuken and Lindhout, 2004), and wheat (Miura et al, 2002; Liu et al, 2006)

Methods

Results

Conclusion