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The carotenoid biosynthetic pathway was genetically manipulated using the recombinant PAC (Phytoene synthase-2A-Carotene desaturase) gene in Korean soybean (Glycine max L. cv. Kwangan). The PAC gene was linked to either the β-conglycinin (β) or CaMV-35S (35S) promoter to generate β-PAC and 35S-PAC constructs, respectively. A total of 37 transgenic lines (19 for β-PAC and 18 for 35S-PAC) were obtained through Agrobacterium-mediated transformation using the modified half-seed method. The multi-copy insertion of the transgene was determined by genomic Southern blot analysis. Four lines for β-PAC were selected by visual inspection to confirm an orange endosperm, which was not found in the seeds of the 35S-PAC lines. The strong expression of PAC gene was detected in the seeds of the β-PAC lines and in the leaves of the 35S-PAC lines by RT-PCR and qRT-PCR analyses, suggesting that these two different promoters function distinctively. HPLC analysis of the seeds and leaves of the T2 generation plants revealed that the best line among the β-PAC transgenic seeds accumulated 146 µg/g of total carotenoids (approximately 62-fold higher than non-transgenic seeds), of which 112 µg/g (77%) was β-carotene. In contrast, the level and composition of the leaf carotenoids showed little difference between transgenic and non-transgenic soybean plants. We have therefore demonstrated the production of a high β-carotene soybean through the seed-specific overexpression of two carotenoid biosynthetic genes, Capsicum phytoene synthase and Pantoea carotene desaturase. This nutritional enhancement of soybean seeds through the elevation of the provitamin A content to produce biofortified food may have practical health benefits in the future in both humans and livestock.

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This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.Plant Breed. Biotech. 2015 (September) is one of the most important crops in the world and in Korea as well. Since the official start of soybean breeding program in Korea at which a landrace 'Jangdanbaekmok' was first released to promote cultivation in 1913, approximately one century has elapsed. Currently, a total of 178 soybean varieties are registered at two representative Korean national institutes, the RDA-Genebank Information Center (http://www.genebank.go.kr) and the Korea Seed & Variety Service (http://www.seed.go.kr). Of these, 155 varieties (87.1%) have been developed through hybridization-based breeding technologies, of which most cultivars (133 varieties, 85.8%) have been released in the last twenty five years. In this review, we attempted to integrate all the information for individual cultivars and to rebuild a breeding pedigree including the entirety of registered Korean soybean varieties. The analysis has resulted in a total of four pedigrees involving 168 cultivars (94.4% out of 178 cultivars), which form the broadest network of pedigrees. Each of pedigrees highlights different key varieties within the context of progenitor networks derived from crossing of various elite parental lines as follows; pedigree I-'Kwangkyo', 'Hwangkeumkong', 'Paldalkong' and 'Sinpaldalkong2', pedigree II-'Baegunkong', 'Jangyeobkong' and 'Keunolkong', pedigree III-'Danyeob', 'Pangsa' and 'Eunhakong'. These pedigrees also reveal purpose (i.e., desirable traits)-driven development of characteristic soybean varieties during the past century of breeding history in Korea. We expect that the pedigree reconstructed in this study will provide breeders with information useful to design breeding schema and guidance towards the genomics-assisted soybean improvement in the future.