Agrobacterium tumefaciens-mediated Transformation of Walnut (Juglans regia)

Abstract

Like many woody plant species, walnut (Juglans regia) can be difficult to genetically transform and regenerate. However, somatic embryos have been used successfully for over two decades as a target tissue for transformation and regeneration of transgenic walnut plants. Walnut somatic embryos, initiated originally from developing zygotic embryos or anther tissue, will proliferate numerous secondary embryos from single cells in the epidermal layer. These single cells in intact somatic embryos can be efficiently transformed by Agrobacterium tumefaciens (A. tumefaciens). This gene transfer system is most efficient when Agrobacterium binary vector plasmids contain a scorable maker gene (e.g. uidA) and a selectable marker gene (e.g. nptII). This system should be applicable to any crop that undergoes repetitive embryogenesis from single Agrobacterium-susceptible cells. Here we describe the method of transforming somatic embryos in detail so that this technique can be applied to walnut and other woody plant species.