The construction of transgenic Forsythia plants: comparative study of three Forsythia species

Forsythia spp. are perennial woody plants containing abundant amounts of beneficial lignans, and the transgenic metabolic engineering of Forsythia is expected to produce plants with a more efficient production of specific lignans on demand. However, the transgenic methods for Forsythia have yet to be fully established. In this study, we have investigated the optimal conditions for the regeneration, growth, and antibiotic-based selection of Forsythia suspense (Fs), F. koreana (Fk), and F. intermedia (Fi), and compared the possibility of the construction of transgenic plants among the three species. Fk, Fi, and Fs explants regenerated more than 100, 36, and 4 shoots per leaf, respectively, revealing that Fk is especially endowed with potent regeneration ability. Fi initiated shoot formation 6 days earlier, but required 6 extra days for the initiation of rooting than the two Forsythia spp. Moreover, Fs, Fk, and Fi displayed different preferences for the components of the MS macro elements in the regeneration media. Fk and Fi calli grew to 10-cm long plants for approximately 120 day. We also found that Fk and Fi exhibited prominent dose-dependent sensitivity to hygromycin, but not to kanamycin. We constructed transgenic hygromycin-resistant Fk and Fi via agrobacterium-based transformation with a hygromycin-resistant gene, hptII. Polymerase chain reaction analyses confirmed the introduction and expression of hptII in the transgenic Fk and Fi. Altogether, these data showed the establishment of the methods for Fk and Fi transgenic plants, and revealed multiple different propensities among Forsythia species.