Fine mapping of the yellow seed locus in Brassica juncea L.

The yellow mustard plant in Northern Shaanxi is a precious germplasm, and the yellow seed trait is controlled by a single recessive gene. In this report, amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) techniques were used to identify markers linked to the brown seed locus in an F(2) population consisting of 1258 plants. After screening 256 AFLP primer combinations and 456 pairs of SSR primers, we found 14 AFLP and 2 SSR markers that were closely linked to the brown seed locus. Among these markers, the SSR marker CB1022 showed codominant inheritance. By integrating markers previously found to be linked to the brown seed locus into the genetic map of the F(2) population, 23 markers were linked to the brown seed locus. The two closest markers, EA02MC08 and P03MC08, were located on either side of the brown seed locus at a distance of 0.3 and 0.5 cM, respectively. To use the markers for the breeding of yellow-seeded mustard plants, two AFLP markers (EA06MC11 and EA08MC13) were converted into sequence-characterized amplified region (SCAR) markers, SC1 and SC2, with the latter as the codominant marker. The two SSR markers were subsequently mapped to the A9/N9 linkage group of Brassica napus L. by comparing common SSR markers with the published genetic map of B. napus. A BLAST analysis indicated that the sequences of seven markers showed good colinearity with those of Arabidopsis chromosome 3 and that the homolog of the brown seed locus might exist between At3g14120 and At3g29615 on this same chromosome. To develop closer markers, we could make use of the sequence information of this region to design primers for future studies. Regardless, the close markers obtained in the present study will lay a solid foundation for cloning the yellow seed gene using a map-based cloning strategy.