Abstract
We investigated the molecular basis of an extremely late bolting, non-heading ‘Leafy Green Parental Line No. 2 (Tsukena No. 2)’, to obtain suitable DNA markers for breeding the late bolting trait in Chinese cabbage (Brassica rapa L. ssp. pekinensis). We found that Tsukena No. 2 contains a ~5 kbp large insertion near the 5′ end of the first intron of BrFLC2, BrFLC3 and BrFLC3′, which are homologs of an Arabidopsis repressor gene for floral transition, FLOWERING LOCUS C (FLC). The transcript abundance of BrFLC1 in Tsukena No. 2 was repressed during cold exposure to the same level as found in a mid-season bolting commercial F1 variety “Muso” (heading Chinese cabbage) and an early-bolting parent of commercial F1 varieties, “Early” (Sakata Co.), whereas repression of BrFLC2 and BrFLC3 containing the large insertion was weak. Furthermore, QTL analysis of a F2 population derived from the Tsukena No. 2 × “Early” revealed that polymorphisms at the BrFLC2 and BrFLC3 loci explained 46.0 and 9.9 % of the phenotypic variation in the bolting time of vernalized plants, respectively. In Arabidopsis, cold-induced repression of FLC and maintenance of that repression are associated with the first intron of FLC. Our study suggests that a naturally occurring large insertion in the first intron resulted in weak repression of BrFLC2 and BrFLC3 during cold exposure and therefore explains the extremely late bolting of the Tsukena No. 2 cultivar.
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Acknowledgments
This study was supported by “Development of extremely late bolting cultivars in Brassicaceae using molecular analysis of a breeding material which requires long-day for bolting”, Adaptable and Seamless Technology Transfer Program through Target-driven Research & Development, Japan Science and Technology Agency. We would like to thank to Professor Ryo Ohsawa in the University of Tsukuba for support of the construction of linkage map and QTL analysis. We also would like to thank to Dr. Karen S. for a review of our manuscript.
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Kitamoto, N., Yui, S., Nishikawa, K. et al. A naturally occurring long insertion in the first intron in the Brassica rapa FLC2 gene causes delayed bolting. Euphytica 196, 213–223 (2014). https://doi.org/10.1007/s10681-013-1025-9
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DOI: https://doi.org/10.1007/s10681-013-1025-9