Abstract
Fatty acid (FA) composition is the typical quantitative trait in oil seed crops, of which study is not only closely related to oil content, but is also more critical for the quality improvement of seed oil. The double haploid (DH) population named KN with a high density SNP linkage map was applied for quantitative trait loci (QTL) analysis of FA composition in this study. A total of 406 identified QTL were detected for eight FA components with an average confidence interval (CI) of 2.92 cM, the explained phenotypic variation (PV) value ranged from 1.49 to 45.05%. Totally, 204 consensus and 91 unique QTL were further obtained via meta-analysis method for the purpose of detecting multiple environment expressed and pleiotropic QTL, respectively. Of which, 74 stable expressed and 22 environmental specific QTL were also revealed, respectively. In order to make clear the genetic mechanism of FA metabolism at individual QTL level, conditional QTL analysis was also conducted and more than two thousand conditional QTL which could not be detected under the unconditional mapping were detected, which indicated the complex interrelationship of the QTL controlling FA content in rapeseed. Through comparative genomic analysis and homologous gene annotation, 61 candidates related to acyl lipid metabolism were identified underlying the CI of FA QTL. To further visualize the genetic mechanism of FA metabolism, an intuitive and meticulous network about acyl lipid metabolism was constructed and some closely related candidates were positioned. This study provided a more accurate localization for stable and pleiotropic QTL, and a deeper dissection of the molecular regulatory mechanism of FA metabolism in rapeseed.
Highlights
Rapeseed (Brassica napus L., genome AACC, 2n = 38) is the second largest oil crop in the world, which can provide affluent edible oil for diet and valuable source for industrial biodiesel (Kimber and Mcgregor, 1995)
The three monounsaturated Fatty acid (FA) (MUFAs) C18:1, C20:1, and C22:1 displayed bi-modal distribution pattern, which indicated that these compositions might be controlled by a few major genes with a relatively large effect
The frequency distribution of the remaining five FA compositions displayed normal or near-normal distribution, which implied that these compositions were typical for the quantitative composition and were controlled by various loci with small genetic effect (Figure 1)
Summary
Revealing the genetic mechanism of FA biosynthesis, increasing the production and improving the quality of seed oil, are the main purpose of breeding program in B. napus. Despite several studies have been performed for the QTL analysis of FA in rapeseed, the deficiencies of lower resolution and credibility, poor precision of the detected QTL still exist due to few years and sites of field trial, low marker density, and smaller size of the mapping populations were used (Burns et al, 2003; Hu et al, 2006; Zhao et al, 2008; Smooker et al, 2011; Yan et al, 2011; Wang et al, 2015), and obtained results were hardly applied to practical breeding program due to lower credibility and large CI. The effort for identification of environmental stable and specific QTL to meet the actual demand of breeding program in B. napus is profound and the field trials with multiple breeding sites, as well as multiyear can facilitate goal achievement
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