Second generation physical and linkage maps of yellowtail (Seriola quinqueradiata) and comparison of synteny with four model fish

Abstract

Background: Physical and linkage maps are important aids for the assembly of genome sequences, comparative analyses of synteny, and to search for candidate genes by quantitative trait locus analysis. Yellowtail, Seriola quinqueradiata, is an economically important species in Japanese aquaculture, and genetic information will be useful for DNA-assisted breeding. We report the construction of a second generation radiation hybrid map, its synteny analysis, and a second generation linkage map containing SNPs (single nucleotide polymorphisms) in yellowtail.

Results: Approximately 1.4 million reads were obtained from transcriptome sequence analysis derived from 11 tissues of one individual. To identify SNPs, cDNA libraries were generated from a pool of 500 whole juveniles, and the gills and kidneys of 100 adults. 9,356 putative SNPs were detected in 6,025 contigs, with a minor allele frequency ≥ 25%. The linkage and radiation hybrid maps were constructed based on these contig sequences. 2,081 markers, including 601 SNPs markers, were mapped onto the linkage map, and 1,532 markers were mapped in the radiation hybrid map.

Conclusions: The second generation linkage and physical maps were constructed using 6,025 contigs having SNP markers. These maps will aid the de novo assembly of sequencing reads, linkage studies and the identification of candidate genes related to important traits. The comparison of marker contigs in the radiation hybrid map indicated that yellowtail is evolutionarily closer to medaka than to green-spotted pufferfish, three-spined stickleback or zebrafish. The synteny analysis may aid studies of chromosomal evolution in yellowtail compared with model fish.

Figure 1

Gene Ontology assignment for assembled contigs. (A) Molecular function, (B) Biological process and (C) Cellular component assignment.

Figure 2

Examples of two linkage groups (female and male). Squ1 has 53 and 48 markers, including 20 and 14 SNPs, in the female and male, respectively. Squ2 has 82 and 77 markers, including 11 and 11 SNPs, in the female and male, respectively. Distances between markers are shown in centiMorgans (cM).

Figure 3

Examples of four radiation hybrid (RH) groups. Each group has 79 markers in SQ1, 70 markers in SQ2, 60 markers in SQ3 and 69 markers in SQ4. Distances between markers are shown in centiRays (cR).

Figure 4

Oxford grids showing conservation of synteny between yellowtail and four model fish. A: medaka, B: zebrafish, C: three-spined stickleback, D: green spotted pufferfish. Each box is highlighted as follows: 0–4: white square, 5–10: yellow square, 11–20: green square, 21–30: sky blue square, 31–40: blue square, more than 40: dark blue square.