Development of transgenic strawberry plants expressing monellin, a sweet protein

Leaf discs from ‘Yeobong’ and ‘Maehyang’ strawberry plants were used as explants for transformation. The Agrobacterium tumefaciens strain EHA105 harboring the monellin gene under the control of the CaMV 35S promoter was used in co-cultivation experiments. The frequencies of callus formation and plant regeneration from leaf explants after co-cultivation in ‘Yeobong’ were higher than those of ‘Maehyang’. These transgenic plants showed normal growth patterns and flowering. PCR and Southern hybridization confirmed that 1 to 2 copies of the monellin gene were integrated into genome of the transgenic strawberry plants. Northern blot analysis confirm that the transcripts were expressed in transgenic strawberry plants. Although long-term subcultured transgenic strawberry plants showed a phenomenon to escape the transgene, the transformation system established in this study provides new opportunities for genetic improvement of strawberry plants.