Identifying genes and mechanisms that provide resistance to scab

My laboratory is using genomics technologies to identify genes and mechanisms that provide resistance to barley and wheat scab. Fusarium graminearum infects wheat and barley and causes severe yield loss. In addition, grain quality is reduced due to the accumulation of deoxynivalenol (DON) and other mycotoxins.  During infection and accumulation of DON, wheat and barley induce a defense response consisting of the expression of hundreds of genes. Our overall objective is to identify a small subset of genes from these hundreds of genes that provide resistance to scab.  The Affymetrix GeneChip technology provides the ability to monitor the expression of 22,000 and 61,000 genes in barley and wheat, respectively. We used this technology to monitor gene expression in resistant and susceptible barley and wheat genotypes during infection and inoculation with DON. In our first set of experiments we identified over 450 barley genes that responded to infection. Next, we identified a set of 69 barley genes that specifically respond to mycotoxin accumulation. We also identified sets of genes that are differentially expressed between resistant and susceptible wheat and barley genotypes.  Recently, we identified over 100 barley genes that are specifically expressed after DON inoculation. Based on extensive analysis of these barley and wheat genes, we identified a subset of approximately 100 genes that may provide some level of resistance. Our challenge now is to identify the genes from this set of 100 that provide resistance.  To systematically test these genes, we established a novel approach to individually examine these genes in wheat for resistance to scab.  Over the next few months we plan to begin to test these genes for resistance. 

Developing transgenic wheat with resistance to scab
Plants defend themselves from pathogens through expressing a large set of genes that are referred to as defense response genes.  One approach to fungal resistance is to express these defense response genes at a high level in transgenic wheat.  The idea is that increased expression of a defense response gene will provide resistance to scab. My laboratory has developed a large set of transgenic wheat lines that express a large set of potential scab resistance genes. We have identified many lines that exhibit reduced scab severity compared to non transgenic controls in multiple greenhouse screens.  In the summer of 2007, we conducted field screens of our best transgenic wheat lines (collaboration with Dr. Ruth Dill-Macky, University of Minnesota).  From the field screen in 2007, we identified six lines that exhibit significant reductions in scab severity.  Combined with our previous field screens in 2004, 2005, and 2006, we have identified 12 lines that exhibit reductions in scab symptoms.

-- Gary J. Muehlbauer, Department of Agronomy and Plant Genetics, University of Minnesota