Pierce’s Disease control through PGIP expression in grafted rootstock
Pierce’s Disease (PD) is the bacterial leaf scorch disease of grapevines caused by Xylella fastidiosa (Xf) and characterized by marginal leaf necrosis, premature leaf blade abscission, and uneven wood maturation. The bacteria use a polygalacturonase (PG) and other putative cell wall modifying enzymes to digest the barriers separating adjoining xylem vessels within the grapevine. The resulting systemic spread of the bacteria throughout the grapevine’s xylem network leads to the progression of PD symptoms. Transgenic grapevines expressing a PG-inhibiting protein (PGIP) from pear fruit exhibit reduced PD symptom development as Xf is effectively constrained to the initially inoculated vessels. The pear PGIP is also graft transmissible, meaning its activity can be passed from a transgenic rootstock to a wild-type grapevine scion. We are currently exploring the effectiveness of this grafting strategy in greenhouse and field-tested grapevines challenged with both natural and artificial PD pressures.
The PG-PGIP relationship has been studied in many backgrounds to better understand the plant cell wall-mediated mechanisms leading to fruit ripening and disease susceptibility. PGIPs exhibit great specificity in their inhibition spectra. In addition to the above work, we are also trying to elucidate the factors influencing potential XfPG inhibition by PGIPs from many plant sources. A PGIP maximally inhibiting XfPG would be an optimal candidate for PD resistance, as delivered from transgenic rootstocks. We are using predictive structure modeling to identify candidate PGIPs and testing their activity against XfPG in vitro and in planta.
This work was funded by the California Department of Food and Agriculture (CDFA) Initiative on Glassy Winged Sharpshooter and Pierce’s Disease
Zac Chestnut (Plant Biology Graduate Group PhD student) and Ravi Barabote (Post-doc) are currently working on this project with Constanza Jackson (Davis Senior High School student) and Ali Spurgeon (UC Davis undergraduate).
http://www.piercesdisease.org/projects/314 (field trial)
http://www.piercesdisease.org/projects/289 (rootstock PGIPs)
The antibody report doesn’t have a page on the PD website yet, but you can attach the Symposium Proceedings report or link to the whole Proceedings here: http://www.cdfa.ca.gov/pdcp/2010_Research_Proceedings.html.