Genome-wide discovery of DNA polymorphism in Brassica rapa.

Single nucleotide polymorphisms (SNPs) and/or insertion/deletions (InDels) are frequent sequence variations in the plant genome, which can be developed as molecular markers for genetic studies on crop improvement. The ongoing Brassica rapa genome sequencing project has generated vast amounts of sequence data useful in genetic research. Here, we report a genome-wide survey of DNA polymorphisms in the B. rapa genome based on the 557 bacterial artificial clone sequences of B. rapa ssp. pekinensis cv. Chiifu. We identified and characterized 21,311 SNPs and 6,753 InDels in the gene space of the B. rapa genome by re-sequencing 1,398 sequence-tagged sites (STSs) in eight genotypes. Comparison of our findings with a B. rapa genetic linkage map confirmed that STS loci were distributed randomly over the B. rapa whole genome. In the 1.4 Mb of aligned sequences, mean nucleotide polymorphism and diversity were theta = 0.00890 and pi = 0.00917, respectively. Additionally, the nucleotide diversity in introns was almost three times greater than that in exons, and the frequency of observed InDel was almost 17 times higher in introns than in exons. Information regarding SNPs/InDels obtained here will provide an important resource for genetic studies and breeding programs of B. rapa.