Validation And Fine Mapping Of The Major QTL Controlling Leaf Lobes In Brassica Rapa

Leaf shape was of vial importance for the photosynthetic rate and yield in plants. During the length of natural and artifical selection, a highlevel of variation in leaf shape, including the leaflobes, is present in Brassica rapa. In our previous study, a major QTL-lobl0.1 controlling leaf lobes was detected at the bottom of linkage group A10 basing on an F2 population which was developed from the maternal parent Brassica rapa L. ssp. Dichotoma RcBr and the male parent Brassica rapa L. ssp. Pekinensis 08A061. In this study, we validate the detected major QTL by developing QTL-NILs. The NIL-F2 population was developed for fine mapping the lob10.1 and the candidate gene was also predicted in this region. The results are as follows:1. An F2 plant without leaf lobes that was homozygous in the targeted region for marker alleles from the male parent (08A061), was backcrossed to RcBr, the recurrent parent with leaf lobes. The QTL-NIL was developed through four cycles of backcrossing followed by one cycle of self-pollination. The estimated length of substituted chromosomal segment in the NILs, lob10.1-NIL, was only 5.6cM and representing 99.45% of the RcBr genome. Compared to RcBr, the recurrent parent, all the NILs showed the absence of leaf lobes and had no significiant differences in other agriculturally important traits.2. For fine mapping the lob 10.1, a NIL-F2 population were developed from the cross between RcBr and lob10.1-NIL. The presence and absence for leaf lobes in the NIL-F2 population fits to 3:1 very well, which indicated the leaf lobe was controlled by one recessive gene in RcBr background. A total of 1180 individuals, absence of leaf lobes, were selected for fine mapping of the major QTL. Seven polymorphic primers between two flanking markers BrID 10909 and BrID 10233 were used to screen the recombinant. Finally, the gene controlling leaf lobes was mapped in a physical distance of 46.5kb, between marker WXInDel-31 and BrID 10909. A total of 12 genes lie in the region, Bra009479-Bra009490.3. Basing on gene annotation in this region, we find that the gene Bra009485 has similar function with genes AT5G04110 in Arabidopsis. AT5G04110 makes function at LP.02 two leaves visible stage, LP.04 four leaves visible stage, LP.06 six leaves visible stage, LP.08 eight leaves visible stage, LP.10 ten leaves visible stage and LP.12 twelve leaves visible stage in DNA topoisomerase activity. Six pairs of primers are designed basing on the sequence of Bra009485. One pair of primer-Bra4 designed on Bra009485 gene promoter region is found to have different amplified bands between the two parents. Thus, we predict Bra009485 is the candidate gene controlling the leaf lobes in Brasssica rapa.