Fine Mapping of the QTL cqSPDA2 for Chlorophyll Content in Brassica Napus L.

Background: Chlorophyll is the most important factor enabling plants to absorb, transfer and transform light energy and plays an important role in yield formation. Brassica napus is one of the most important oil crops. Qinghai Province is located in the Qinghai-Tibet Plateau in China. Solar radiation and its intensity are higher, and the light duration is longer. Under this light condition, conducting high light efficiency breeding of Brassica napus from the perspective of improving photosynthetic efficiency has considerable social and economic value. At present, the fine mapping of chlorophyll quantitative trait loci (QTLs) in many crops has been studied, especially in rice. In Brassica napus, there have been studies on the initial location of chlorophyll in seed embryos and pericarps, but there are few reports on the fine mapping of chlorophyll QTLs. We built near-isogenic lines, fine mapped the chlorophyll locus, and evaluated the effect of the dominant locus on agronomic traits.Results: The cqSPDA2 locus was mapped in an interval of 21.87-22.91 Mb on the A02 chromosome of Brassica napus using doubled haploid (DH) lines. To fine map cqSPDA2, we built near-isogenic lines and designed Indel primers covering the mapping interval. The 469 individuals in the BC3F2 population were analyzed using these Indel primers. Among the Indel primers, 15 narrowed the mapping interval to 5.2 cM between Indel3 and Indel15. Next, 16 Indel primers and 19 SSR primers were designed within the new narrow mapping interval, and 7 primers were polymorphic and tightly linked to the cqSPDA2 locus in the BC4F2 population. The mapping interval was narrowed to 152 kb on A02 between SSR2 and Indel15. We found three annotated genes in the mapping interval, including BnaA02g30260D, BnaA02g30290D and BnaA02g30310D, which may be responsible for chlorophyll synthesis by gene expression analysis. Conclusions: The locus cqSPDA2, the dominant QTL for chlorophyll content in Brassica napus, was fine mapped to the 21.89-22.04 Mb interval on A02. Three annotated genes (BnaA02g30260D, BnaA02g30290D and BnaA02g30310D) which may be responsible for chlorophyll synthesis were found.