Development of efficient transformation systems for functional genomic research in apple

Apple has become a model species for Rosaceae genetic and genomic research, but it is difficult to obtain transgenic apple plants. Transgenic lines have been obtained from a number of genotypes, but the efficiency of apple transformation is not high. In the past several years, we developed an efficient regeneration and Agrobacterium-mediated transformation system for apple using cotyledons as explants. The proximal cotyledons, excised from apple seedlings that emerged from mature embryos cultured for 10-14 d in vitro, were suitable as explants for Agrobacterium-mediated transformation, and the percentage of explants with kanamycin-resistant buds was about 10%. At the same time, one in vitro seedling clone with high regeneration capacity was developed from the open-pollinated seeds of apple. The seedling clone, named GL-3, was also susceptible to Agrobacterium. After the leaf segments of GL-3 were transformed with A. tumefaciens strain EHA105 carrying the AtmiR156a antisense gene, the percentage of explants with kanamycin-resistant buds reached 27.5%. Our results lay a foundation for apple functional genomic research.