A sequence-tagged linkage map of Brassica rapa.

A detailed genetic linkage map of Brassica rapa has been constructed containing 545 sequence-tagged loci covering 1287 cM, with an average mapping interval of 2.4 cM. The loci were identified using a combination of 520 RFLP and 25 PCR-based markers. RFLP probes were derived from 359 B. rapa EST clones and amplification products of 11 B. rapa and 26 Arabidopsis. Including 21 SSR markers provided anchors to previously published linkage maps for B. rapa and B. napus and is followed as the referenced mapping of R1-R10. The sequence-tagged markers allowed interpretation of the pattern of chromosome duplications within the B. rapa genome and comparison with Arabidopsis. A total of 62 EST markers showing a single RFLP band were mapped through 10 linkage groups, indicating that these can be valuable anchoring markers for chromosome-based genome sequencing of B. rapa. Other RFLP probes gave rise to 2-5 loci, inferring that B. rapa genome duplication is a general phenomenon through 10 chromosomes. The map includes five loci of FLC paralogues, which represent the previously reported BrFLC-1, -2, -3, and -5 and additionally identified BrFLC3 paralogues derived from local segmental duplication on R3.