Review of Factors Affecting Organogenesis, Somatic Embryogenesis and Agrobacterium tumefaciens- Mediated Transformation of Strawberry

Standardization of an efficient regeneration system for each strawberry genotype is generally an indispensible pre-requisite for the successful development of transgenic plants. In this paper, we review some key factors affecting the regeneration of strawberry plants via adventitious organogenesis or somatic embryogenesis, such as type of explant, growth regulators or dark/light treatments. Since Agrobacterium tumefaciens-mediated transformation is the method of choice for strawberry transformation, we review the strategies adopted by different scientists to achieve higher transformation efficiencies and recovery of marker-free transgenic plants. Sufficient Agrobacterium cells during cocultivation, an adequate cocultivation period, the use of vir gene inducers like acetosyringone, introduction of a preselection phase between co-cultivation and selection, and optimum selection pressure, are all important factors to obtain stable transformants. For effective transformation, the antibiotic regime should control bacterial growth without inhibiting the regeneration of plant cells. A general protocol for the Agrobacterium transformation of strawberry leaf discs is also described. Finally, we discuss the metrics employed by different researchers for measuring the success of transformation, and highlight the difference between transformation efficiency and transformation percentage. _____________________________________________________________________________________________________________