| Since their inception, genetically engineered (GE)-crops have provided environmental and economic benefits on a global scale. However, various issues such as regulatory costs, gene flow concerns, and consumer perceptions of food safety, have hampered the widespread adoption of this technology. A novel biotechnology application, consisting of a transgenic rootstock and wild-type scion (called a trans-graft), has potential to provide the benefits of GE-crops while addressing gene flow concerns, and perhaps even garner greater consumer acceptance. In addition, trans-grafted crops may facilitate the incorporation of GE-specialty crops into consumer markets by allowing multiple scions to be utilized with a single deregulated GE-rootstock. Before trans-grafted plants enter the translational pipeline, regulatory considerations will need to be addressed. Of fundamental importance will be a comprehensive experimental framework that determines the presence or absence of transgenic proteins and nucleic acids in the scion in a quantifiable manner. At present, no science-based regulatory framework exists that would accomplish this. Determining the maximum allowable threshold of transgenic material that can be present in a scion and still allow its classification as non-GE material will ultimately depend on regulators and legislators. However, this process is unlikely to proceed without experimental precedent.;In order to provide an example of this framework, Crown Gall-resistant walnut lines producing siRNAs, and Xylella fastidiosa and Botrytis cinerea-resistant grape lines producing pear polygalacturonase-inhibiting protein (pPGIP) were examined along with their transgenic counterpart in a tomato model. Constructs consisted of cytoplasmic marker-genes GUS and NPTII, apoplast-targeted pPGIP, and two siRNA hairpins, IPT and IAAM. During the examination of these plants, no instances of gDNA or mRNA mobility were detected. Cytosolic marker-proteins, GUS and NPTII, were not detected in any scion material either. Significantly, it was discovered that transgenic siRNAs accumulated across the graft-junction in walnut kernel, but not in tomato fruit, nor in any leaf tissue by our detection method. In addition, translocation of apoplast-targeted pPGIP protein in grape and tomato leaves did not occur to the extent expected based on previous studies in grape. Thus, generalized notions of transgene mobility derived from model plant systems may not necessarily be applicable to other plant systems and should be interpreted with reservation.;The experimental framework outlined here serves as a basis for researchers to expand upon, and learn which techniques are most applicable to addressing questions regarding trans-grafting. This report also provides an example to regulatory bodies of the type data that will be generated and need to be interpreted prior to scion equivalency determinations. |
