IMPROVING OUR UNDERSTANDING OF SUBSTANCE TRANSPORT ACROSS GRAFT UNIONS

• Author(s): Cousins, Peter; Reisch, Bruce; Eom, Seok-Hyun; Kikkert, Julie;
• Abstract: The goal of this project is to determine whether it is possible to mobilize proteins from rootstocks to scions via xylem transport. Xylem-mobile gene products may provide a means for control of Pierces disease (PD). Multiple lines of transgenic grapevines containing NPT-II, endochitinase, and GUS/NPT-II fusion genes are being used to investigate the movement of transgene products across graft unions into non-transgenic scions. These transgenic lines produce proteins that differ in molecular weight [29 kDa (NPT-II), 42 kDa (endochitinase), and 97 kDa (GUS/NPT-II fusion product)] as well as concentration. Lines were chosen for either high or low levels of expression in order to determine whether the root concentration of each protein would affect levels found in non-transgenic scions. To determine transgenic protein concentrations in root tissues, protein assays were conducted using in-vitro grown transgenic vines corresponding to the lines grown in the field. ELISA assays were used to determine NPT-II protein concentrations (g/g protein). Chitinase activity was determined according to a fluorescence assay. As results of these assays, selected transgenic lines were chosen for use as rootstocks with non-transgenic Chardonnay scions. More than five grafted vines of each desired combination were created via either chip-budding or approach grafting. Non-transgenic scion tissues will be assayed for the presence of rootstock-produced transgenic proteins to enhance our understanding of substance transport across graft unions. Initial testing indicates that the 97 kDa GUS/NPT-II fusion product does not move across graft unions.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium