Transformation of European ash (Fraxinus excelsiorL.) callus as a starting point for understanding the molecular basis of ash dieback

Plant genetic engineering requires transfer of genetic material into plant cells, a process that is frequently challenging for tree species. Here we report first successful genetic transformation of European ash ( Fraxinus excelsior ). The protocol relies on the use of Agrobacterium tumefaciens to transform callus tissue derived from embryos of F. excelsior . In our experiments, we use the β-glucuronidase (GUS) reporter system to demonstrate transformation of ash callus tissue. Moreover, we describe an antibiotic-resistance based selection process enabling formation of stable transgenic callus lines. Since ash dieback threatens the long-term stability of many native F. excelsior populations, we hope that the transformation techniques described in this manuscript will facilitate rapid progress in uncovering the molecular basis of the disease and mechanisms used by trees to resist it.