Scientists Sequence a Cereal Killer
Jennifer Martin, CSREES Staff (202) 720-8188
November 2, 2007
By Stacy Kish, CSREES Staff
Important cereal crops, such as wheat and barley, are susceptible to a fungus, called Fusarium graminearum that is responsible for head blight disease. Researchers recently sequenced and annotated the genome of this fungus, shedding light on how it is able to survive in rapidly changing environments. The new knowledge could lead to new ways to combat the harmful pathogen, which has caused more than $10 billion in crop losses over the past 10 years.
USDA scientist H. Corby Kistler, along with Christina Cuomo of the Broad Institute of MIT and Harvard and colleagues at a consortium of universities and labs around the world, used a whole genome shotgun approach, a faster approach that involves shredding and replicating the genome in order to sequence the Fusarium graminearum genome, bypassing the need for a physical map. The scientists found very few repetitive sequences in the genome. Instead, they discovered that most mutations occur at particular points in the genome sequence, specifically associated with plant-fungus interactions. The specific locations of the high sequence diversity in the genome may explain the ability of the fungus to adapt rapidly to changing environments and hosts.
Plant-fungus interaction is like an intricate game of cat and mouse. If the plant can detect the fungus, it can mount a defense and ward off the fungus. However, the newly identified genome sequence is like a closet full of disguises, cloaking the fungus from plant detection. If the fungus can disguise itself and gain access to the plant, it can override the plant's defenses and cause disease.
The growth of this fungus is largely dependent on weather conditions. The fungus thrives in cool wet conditions and infects unsuspecting fields by releasing an assault of pinprick-sized spores. The tiny spores colonize the edible portion of newly emerging plants and grow down through the stalk. Once a fungal mass is established, the fruiting structures of the fungus penetrate the plant's leaves, in effect suffocating the plant. During the winter, the fungus goes dormant in the debris of the withered, bleached heads of the blighted grain. As spring approaches, the cycle begins again.
To date, cultural disease management strategies, such as crop rotation, tillage practices and field sanitation, resulted in partial control. Preventative application of fungicide has also shown moderate disease control.
The recently identified portion of the Fusarium genome is like the game day playbook for fungal attacks on plants. Future work focused on the high sequence diversity may result in environmentally-friendly ways to combat this important agricultural pathogen.
The results of this research study are presented in the September 7, 2007, issue of the journal Science .
The USDA's Cooperative State Research, Education, and Extension Service (CSREES) funded this research project through the NRI Microbial Genomics program. CSREES advances knowledge for agriculture, the environment, human health and well-being, and communities by supporting research, education and extension programs in the Land-Grant University System and other partner organizations. For more information, visit www.csrees.usda.gov.