Developing Apple Intragenic Transformation Systems

We aim to improve apple transformation systems to facilitate the production of intragenic plants, containing DNA sequences derived solely from apple, and thereby enhance the marketability of novel apple cultivars generated via genetic modification. Significant progress has been made in a number of areas. The cytokinin transformation vectors, developed by J.R. Simplot Co., containing the isopentenyl transferase (IPT) gene located in the vector backbone were tested in apple. Our results show that IPT gene expression confers a bushy phenotype on apple plants, and can be used for early identification and elimination of transformed apple plants containing undesirable vector backbone sequences. However, IPT transcribed from the potato ubiquitin promoter did not significantly enhance apple shoot regeneration on cytokinin-free media, whereas use of a CaMV35S driven IPT gene did enhance apple shoot regeneration on cytokinin-free media. We have also generated derivatives of the apple acetolactate synthase gene using site-specific mutagenesis, that confer chlorsulfuron resistance, demonstrating the potential of using an apple-derived gene as a selectable marker for apple transformation. In addition, we have identified apple DNA sequences that can function as T-DNA border elements. With Plant & Food Research's identification and characterisation of several apple genes and regulatory elements that confer novel and beneficial traits, we are now well placed to produce intragenic apple trees with commercial potential.