The cultivated strawberry (Fragaria× ananassa) is an octoploid (2n = 8x = 56) of the Rosaceae family whose genomic architecture is still controversial. Several recent studies support the AAA′A′BBB′B′ model, but its complexity has hindered genetic and genomic analysis of this important crop. To overcome this difficulty and to assist genome-wide analysis of F. × ananassa, we constructed an integrated linkage map by organizing a total of 4474 of simple sequence repeat (SSR) markers collected from published Fragaria sequences, including 3746 SSR markers [Fragaria vesca expressed sequence tag (EST)-derived SSR markers] derived from F. vesca ESTs, 603 markers (F. × ananassa EST-derived SSR markers) from F. × ananassa ESTs, and 125 markers (F. × ananassa transcriptome-derived SSR markers) from F. × ananassa transcripts. Along with the previously published SSR markers, these markers were mapped onto five parent-specific linkage maps derived from three mapping populations, which were then assembled into an integrated linkage map. The constructed map consists of 1856 loci in 28 linkage groups (LGs) that total 2364.1 cM in length. Macrosynteny at the chromosome level was observed between the LGs of F. × ananassa and the genome of F. vesca. Variety distinction on 129 F. × ananassa lines was demonstrated using 45 selected SSR markers.
A total of 20 P1 clones with an average insert size of 80 kb and each containing a marker(s) specifically mapped on chromosome 5 were isolated from a P1 library of the Arabidopsis thaliana genome, and their nucleotide sequences were determined according to a shotgun-based strategy and precisely located on the physical map of chromosome 5 separately constructed. The total length of the sequenced regions were summed up to 1,621,245 bp. By comparison with the sequences in protein and EST databases and analysis with computer programs for gene modeling, a total of 347 potential protein-coding genes and/or gene segments with known or predicted functions were identified. The positions of exons which do not exhibit any similarity to known genes were also predicted. An average density of the genes and/or gene segments assigned so far as 1 gene/4,672 bp. Introns were identified in approximately 78% of the potential genes, and the average number and length of the introns per gene were 3.7 and 161 bp. The transcription level of the predicted genes was roughly monitored by counting the numbers of identified Arabidopsis ESTs. The sequence data and gene information are available through the World Wide Web at http:/(/)www.kazusa.or.jp/arabi/.
Genome-wide genotyping data regarding breeding materials are essential resources for improving breeding efficiency, especially in plants with complex genomes with a high degree of polyploidy. Several current breeding efforts in cultivated peanut (Arachis hypogaea L.), which has a tetraploid genome, are devoted to developing high oleic acid cultivars. Genetic maps for such breeding programs have been developed using simple-sequence repeat (SSR) markers, the use of which requires time-consuming electrophoretic analyses. Next-generation sequencing (NGS) technology can overcome this technical hurdle. Initially, we attempted double-digest restriction siteassociated DNA sequencing on peanut breeding materials used to develop high oleic acid cultivars. However, this method was not effective because few single nucleotide polymorphism (SNPs) were available because of low genetic diversity of the lines.
A fine physical map of Arabidopsis thaliana chromosome 5 was constructed by ordering the clones from YAC, P1, TAC and BAC libraries of the genome using the sequences of a variety of genetic and EST markers and terminal sequences of clones. The markers used were 88 genetic markers, 13 EST markers, 87 YAC end probes, 100 YAC subclone end probes, and 390 end probes of P1, TAC and BAC clones. The entire genome of chromosome 5, except for the centromeric and telomeric regions, was covered by two large contigs 11.6 Mb and 14.2 Mb long separated by the centromeric region. The minimum tiling path of the chromosome was constituted by a total of 430 P1, TAC and BAC clones. The map information is available at the Web site http://www.kazusa.or.jp/arabi/.
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