Wheat Transformation: a Needed Tool for Wheat Genetics and Germplasm Improvement

Fusarium head blight (FHB) is a major disease of wheat in the north central and eastern United States that affects both grain yield and end-use quality. It is generally agreed that the most cost effective way of preventing this disease would be through the release of FHB resistant cultivars. A major limitation to developing FHB resistant cultivars is the limited availability of resistant germplasm. Our project has attempted to increase genetic resources expressing FHB resistance through wheat transformation. Though microprojectile bombardment is commonly used, wheat transformation using Agrobacterium tumefaciens is preferred because a higher probability of simple, low copy integration events and ease in generating ‘marker-free’ transgenic lines by simultaneous delivery of two T-DNA elements. Currently we are using two strategies for increasing FHB resistance. The first strategy relies upon anti-fungal protein expression, such as bovine lactoferrin along with its derivative bovine lactoferricin, and the synthetic lytic peptide D4E1. The second strategy is to develop lines expressing inhibitors of programmed cell death (anti-apoptotic genes; Bcl-xL, Op-IAP, Sf-IAP, and ced9). FHB and its toxin, deoxynivalenol, have been suggested to regulate programmed cell death during pathogen infection. By transforming wheat with inhibitors of programmed cell death we hope to not only increase tolerance to FHB in wheat, but inhibit necrotrophic pathogen infection in general. The expression of inhibitors of programmed cell death may result in other agronomically beneficial traits as well. Preliminary results suggest improved tolerance to high levels of salinity and cold stress, as transgenic plants demonstrate reduced levels of DNA fragmentation and increased hardiness, respectively. We have also demonstrated the ability of deoxynivalenol to induce increased levels of programmed cell death via TUNEL staining of treated leaf sections. Finally, while our interest lays in the augmentation of FHB resistance present in wheat and its relatives, the importance of wheat transformation as a key genomics tools is clear. Transformation technology provides the ability to insert beneficial genes as well as silence existing genes in order to elucidate host-pathogen interactions during necrotrophic infection. For example, a newly discovered extremely efficient gene silencing system called DRIGS (direct repeat induced post transcriptional gene silencing) is currently being tested in wheat.