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Novel genomic approaches unravel genetic architecture of complex traits in apple.

Kumar S, Garrick DJ, Bink MC, Whitworth C, Chagné D, Volz RK - BMC Genomics (2013)

Bottom Line: Genomic regions were identified, some of which coincided with known candidate genes, with significant effects on various traits.Correlations between allele substitution effects obtained from single-marker and all-marker analyses were about 0.90 for all traits.Genomic regions with probable pleiotropic effects were supported by the corresponding higher linkage group (LG) level estimated genetic correlations.

View Article: PubMed Central - HTML - PubMed

Affiliation: The New Zealand Institute for Plant & Food Research Limited, Private Bag 1401, Havelock North 4157, New Zealand. Satish.Kumar@plantandfood.co.nz

ABSTRACT

Background: Understanding the genetic architecture of quantitative traits is important for developing genome-based crop improvement methods. Genome-wide association study (GWAS) is a powerful technique for mining novel functional variants. Using a family-based design involving 1,200 apple (Malus × domestica Borkh.) seedlings genotyped for an 8K SNP array, we report the first systematic evaluation of the relative contributions of different genomic regions to various traits related to eating quality and susceptibility to some physiological disorders. Single-SNP analyses models that accounted for population structure, or not, were compared with models fitting all markers simultaneously. The patterns of linkage disequilibrium (LD) were also investigated.

Results: A high degree of LD even at longer distances between markers was observed, and the patterns of LD decay were similar across successive generations. Genomic regions were identified, some of which coincided with known candidate genes, with significant effects on various traits. Phenotypic variation explained by the loci identified through a whole-genome scan ranged from 3% to 25% across different traits, while fitting all markers simultaneously generally provided heritability estimates close to those from pedigree-based analysis. Results from 'Q+K' and 'K' models were very similar, suggesting that the SNP-based kinship matrix captures most of the underlying population structure. Correlations between allele substitution effects obtained from single-marker and all-marker analyses were about 0.90 for all traits. Use of SNP-derived realized relationships in linear mixed models provided a better goodness-of-fit than pedigree-based expected relationships. Genomic regions with probable pleiotropic effects were supported by the corresponding higher linkage group (LG) level estimated genetic correlations.

Conclusions: The accuracy of artificial selection in plants species can be increased by using more precise marker-derived estimates of realized coefficients of relationships. All-marker analyses that indirectly account for population- and pedigree structure will be a credible alternative to single-SNP analyses in GWAS. This study revealed large differences in the genetic architecture of apple fruit traits, and the marker-trait associations identified here will help develop genome-based breeding methods for apple cultivar development.

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Genome-wide average LD decay estimated from first generation (n=1,120) and second generation (n=1,600) individuals.
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Figure 3: Genome-wide average LD decay estimated from first generation (n=1,120) and second generation (n=1,600) individuals.

Mentions: The pattern of LD (r2) decay in our GWAS population of 1120 individuals (arbitrarily called the first generation) was compared with that observed in the successive generation (i.e. second generation; see Methods). Results showed a high degree of LD even at longer distances between markers; for example, in the second generation the average r2 for SNPs separated by 0.1 Mbp, 0.5 Mbp (approximately 1 cM in apple), and 1.0 Mbp was 0.28, 0.21, and 0.16, respectively (Figure 3). This is somewhat lower compared to LD in the first generation (also reported earlier by [6]), but the pattern of LD decay was quite similar in both generations (Figure 3).


Novel genomic approaches unravel genetic architecture of complex traits in apple.

Kumar S, Garrick DJ, Bink MC, Whitworth C, Chagné D, Volz RK - BMC Genomics (2013)

Genome-wide average LD decay estimated from first generation (n=1,120) and second generation (n=1,600) individuals.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3686700&req=5

Figure 3: Genome-wide average LD decay estimated from first generation (n=1,120) and second generation (n=1,600) individuals.
Mentions: The pattern of LD (r2) decay in our GWAS population of 1120 individuals (arbitrarily called the first generation) was compared with that observed in the successive generation (i.e. second generation; see Methods). Results showed a high degree of LD even at longer distances between markers; for example, in the second generation the average r2 for SNPs separated by 0.1 Mbp, 0.5 Mbp (approximately 1 cM in apple), and 1.0 Mbp was 0.28, 0.21, and 0.16, respectively (Figure 3). This is somewhat lower compared to LD in the first generation (also reported earlier by [6]), but the pattern of LD decay was quite similar in both generations (Figure 3).

Bottom Line: Genomic regions were identified, some of which coincided with known candidate genes, with significant effects on various traits.Correlations between allele substitution effects obtained from single-marker and all-marker analyses were about 0.90 for all traits.Genomic regions with probable pleiotropic effects were supported by the corresponding higher linkage group (LG) level estimated genetic correlations.

View Article: PubMed Central - HTML - PubMed

Affiliation: The New Zealand Institute for Plant & Food Research Limited, Private Bag 1401, Havelock North 4157, New Zealand. Satish.Kumar@plantandfood.co.nz

ABSTRACT

Background: Understanding the genetic architecture of quantitative traits is important for developing genome-based crop improvement methods. Genome-wide association study (GWAS) is a powerful technique for mining novel functional variants. Using a family-based design involving 1,200 apple (Malus × domestica Borkh.) seedlings genotyped for an 8K SNP array, we report the first systematic evaluation of the relative contributions of different genomic regions to various traits related to eating quality and susceptibility to some physiological disorders. Single-SNP analyses models that accounted for population structure, or not, were compared with models fitting all markers simultaneously. The patterns of linkage disequilibrium (LD) were also investigated.

Results: A high degree of LD even at longer distances between markers was observed, and the patterns of LD decay were similar across successive generations. Genomic regions were identified, some of which coincided with known candidate genes, with significant effects on various traits. Phenotypic variation explained by the loci identified through a whole-genome scan ranged from 3% to 25% across different traits, while fitting all markers simultaneously generally provided heritability estimates close to those from pedigree-based analysis. Results from 'Q+K' and 'K' models were very similar, suggesting that the SNP-based kinship matrix captures most of the underlying population structure. Correlations between allele substitution effects obtained from single-marker and all-marker analyses were about 0.90 for all traits. Use of SNP-derived realized relationships in linear mixed models provided a better goodness-of-fit than pedigree-based expected relationships. Genomic regions with probable pleiotropic effects were supported by the corresponding higher linkage group (LG) level estimated genetic correlations.

Conclusions: The accuracy of artificial selection in plants species can be increased by using more precise marker-derived estimates of realized coefficients of relationships. All-marker analyses that indirectly account for population- and pedigree structure will be a credible alternative to single-SNP analyses in GWAS. This study revealed large differences in the genetic architecture of apple fruit traits, and the marker-trait associations identified here will help develop genome-based breeding methods for apple cultivar development.

Show MeSH
Related in: MedlinePlus