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My laboratory is using genomics technologies to identify genes and mechanisms that provide resistance to barley and wheat
scab. Fusarium graminearum, the causal scab pathogen, 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 thousands of genes. Our idea is that genes that are expressed either in response to
infection or differentially expressed between genotypes are candidates for playing a role in resistance to scab. Thus, our overall objective is to identify genes from these thousands 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 these technologies to examine the gene expression patterns in barley and wheat during F. graminearum infection and in barley during DON
accumulation. In barley and wheat, we have defined the stages of infection, developed an understanding of the host response to infection, and developed an integrated model for the host response in barley and wheat.
We also identified 14 genes that exhibited expression differences between resistance and susceptible wheat genotypes during F. graminearum infection. In barley, we have identified over 100 genes that exhibit
expression patterns that differentiate resistant and susceptible genotypes. We also identified 255 barley genes that responded to DON. In addition, we initiated a project to sequence expressed genes in resistance
and susceptible wheat genotypes. From these gene discovery efforts, we have identified two promising genes. One gene detoxifies DON and another appears to regulate the host response to DON accumulation.
The best test of a potential gene involved in scab resistance is to develop a transgenic wheat plant and test
the plants for resistance. Unfortunately, developing transgenic wheat is an expensive and time-consuming process. Thus, limiting the number of potential resistance genes that can be tested. To reduce the number of
potential resistance genes for testing in transgenic wheat, we are using a relatively quick assay to examine the function of a set of genes.
Developing transgenic wheat with resistance to scab
Plants defend themselves from pathogens through a variety of responses and mechanisms. One approach to fungal
resistance is to express potential resistance genes at a high level in transgenic wheat. The idea is that increased expression of potential resistance genes 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. These lines will be evaluated this summer in the field as part of Dr. Ruth Dill-Macky’s (University of Minnesota) transgenic wheat trial. We have also initiated development of transgenic
wheat that will carry a gene that detoxifies DON and another gene that appears to play a role in regulating the host response to DON accumulation. -- Gary J. Muehlbauer, Department of Agronomy and Plant Genetics,
Univ. of MN.
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