Erin Ladle and Dr. Jeff Maughan, Plant and Wildlife Sciences

Main Text

Bromus tectorum L., commonly known as cheatgrass, is an invasive annual grass species that dominates millions of hectares of land in the Great Basin area, in the western United States.1 The widespread invasion of cheatgrass has increased fire incidence in some areas of the Great Basin from every 30-100 years to every 5 years. Moreover, once cheatgrass becomes the dominant vegetative species, it monopolizes resources, significantly contributing to the endangerment of many native plant species.

Cheatgrass growth is inhibited by Ustilago bullata Berk., a fungal smut that infects the growing spikelet, destroying the seed. For several years, our group has been working to manipulate the U. bullata pathosystem towards the end goal of biocontrol of cheatgrass. Biocontrol, or the use of biological agents to control the species has been proposed as a cost effective and environmentally sensible method to control cheatgrass invasion and dominance.

Previous research identified a genetic marker that is linked to the virulence gene with an 18.7 cM distance. This gene was mapped through comparative analysis to chromosome 8 of the genome. However, having only one genetic marker is not enough to determine the precise location of the virulence gene.

Our goals from this research project were to 1) identify genetic markers linked to the causal virulence gene in U. bullata and 2) identify candidate virulence genes based on comparative genomic analysis with Ustilago maydis (D.C.) Cda, a closely related species.

The first course of action I took was to identify candidate virulence genes. I researched virulence genes in U. maydis. This species of fungus has been studied very thoroughly and gene and sequence data are easily available, unlike U. bullata. Through the NCBI (National Center for Biotechnology Information) website and Google Scholar Search, I was able to identify the location and sequence of 3 virulence genes found on U. maydis. I created six genetic markers based off of these sequences hoping that the two species were closely related enough to have similar DNA sequences in these chromosome regions. I tested these genetic markers in three different populations of U. bullata. None of these markers were found to be linked with the virulence gene.

My next step was to gather all of the DNA sequence information available from NCBI on chromosome 8 of U. maydis. I then compared the sequence data we had of U. bullata with the sequence of chromosome 8 of U. maydis. By doing this, I was able to create a hypothetical sequence of chromosome 8 of U. bullata. Having this sequence information allowed me to create more specific genetic markers. Through MISA, a biotechnology computer program, I identified 3 microsatellites within chromosome 8 of U. bullata. I was able to create 6 genetic markers based on these findings. After analyzing these genetic markers, I found that none of them are linked with the virulence gene.

We are still in the “identifying” phase of the research project; we need to identify another genetic marker linked with virulence before we can locate and sequence the virulence gene. I feel a little like Thomas Edison when he said, “I haven’t failed, I’ve found 10,000 ways that don’t work”. I never would have expected as much frustration as I have had from this research project. I have learned great lessons of patience and perseverance. We still hope to find a genetic marker, so that we might complete our end goal of sequencing the virulence gene. With this sequence, the biocontrol of cheatgrass will become a much more viable option.

The next course of action is to continue to create genetic markers and analyze them to determine if they are linked with the virulence gene. We hope also that if research goes according to plan then the findings from this project will be presented at the Plant and Animal Genome research conference in San Diego in January 2011.

I plan on continuing to work on this research project until I begin graduate school this coming fall. I will be working towards a Master’s Degree in Genetic Counseling at the University of Utah. There is no doubt in my mind that this research experience is what helped make me such a strong candidate for graduate school. I was accepted to all four of the schools at which I interviewed. The interviewers at each school asked about my experience obtaining this research grant and working on a project. They all seemed impressed by this amazing opportunity I had while still an undergraduate student.

Through this research project I was able to learn many new laboratory skills and I gained greater confidence in the lab. I also really enjoyed being part of a research team. It was a great experience to be able to collaborate and learn from others, including my mentor – Dr. Jeff Maughan, USDA researcher- Dr. Susan Meyer, a professor – Dr. Craig Coleman, to name a few. It was fascinating to get together for meetings on the project and to see how my research project was a part of something much larger than I had initially imagined.

Sources

• Whisenant S G (1990) Changing fire frequencies on Idaho’s Snake River Plains: ecological management implications. In Proceedings-Symposium on Cheatgrass Invasion, Shrub Die-Off, and Other Aspects of Shrub Biology and Management. USDA For Serv Gen Tech Rep 276:4-10 2
• Meyer S, Nelson D L, Clement S (2001) Evidence for resistance polymorphism in the Bromus tectorum-Ustilago bullata pathosystem implications for biocontrol. Can J Plant Pathol 23:19-27