Functional Identification of Apple Baby Boom in Genetic Transformation and Somatic Embryogenesis

Agrobacterium-mediated genetic transformation is inefficient in apple, which limits the development of apple-related research and industry . Using molecular methods to create a new and more efficient method of genetic transformation has become the focus of research, and improving the efficiency of the three key steps of transformation, regeneration, and rooting has become an effective means of achieving this goal. Baby Boom (BBM) is widely used in plant biotechnology as an important transcription factor regulating adventitious shoot regeneration and somatic embryogenesis. A homologous gene, MDP0000125317 , with high amino acid sequence similarity to AtBBM was cloned in this study, and it was identified from the Royal Gala apple genome ( Malus × domestica Borkh.), which was named as MdBBM . The qRT-PCR analysis revealed that MdBBM was expressed at higher levels in the ovary, roots, and seeds. Agrobacterium -mediated transformation of pRI101- MdBBM significantly improved the shoot regeneration efficiency in apples. In the experiment, 33 of the MdBBM-OE transformants were obtained. Compared with the control, only adventitious shoots were formed on the regeneration shoot medium. In vitro leaves of MdBBM-OE transformants were regenerated in three forms: adventitious shoots, adventitious roots, and somatic embryos. Overexpression of MdBBM promoted somatic embryogenesis under 2,4-dichlorophenoxyacetic acid (2,4-D) induction.