Organisms
Outline
Fusarium graminearum
Fusarium graminearum is the causal agent of head blight (scab) of wheat and barley, a plant disease with great impact on U.S. agriculture and society during the past decade. Approximately $3 billion were lost to U. S. agriculture during wheat scab epidemics in the 1990s, resulting in devastating effects on farm communities in the upper Midwest and elsewhere (McMullen et al., 1997; Windels, 2000). Moreover, the disease is becoming a threat to the world's food supply due to recent head blight outbreaks in Asia, Canada, Europe and South America (Dubin et al., 1997). The fungus also infects and causes disease on corn and rice (Webster and Gunnell, 1992; White, 1999). The pathogen poses a two-fold threat: first, infested cereals are significantly reduced in seed quality and yield, and secondly, scabby grain is contaminated with trichothecene and estrogenic mycotoxins, making it unsuitable for food or feed (McMullen et al., 1997). As a food safety issue, trichothecene toxins such as "vomitoxin" (deoxynivalenol) pose a serious hazard to human and animal health because these sesquiterpenoids are potent inhibitors of eukaryotic protein biosynthesis. Vomitoxin causes weight loss and feeding refusal in non-ruminant livestock, and human ingestion of grain contaminated with F. graminearum has been associated with alimentary toxic aleukia as well as illness characterized by nausea, vomiting, anorexia, and convulsions (Murphy and Armstrong, 1995). Trichothecenes also are powerful modulators of human immune function and may promote neoplasms, cause autoimmune disease, or have long-term effects on resistance to infectious disease by altering immune response (Berek et al., 2001; Lindsay, 1997).
Sequenced strain information: The strain chosen for sequencing by the International Gibberella zeae Genomics Consortium (IGGR) was PH-1 (NRRL 31084). Fusarium graminearum is the predominant FHB species causing scab of wheat and barley in North America and Europe and is distributed worldwide (O'Donnell et al., 2000, 2004). Isolated in Michigan, PH-1 is highly fertile (Trail and Common, 2000), produces trichothecenes and zearalenone , sporulates abundantly in pure culture and is highly pathogenic to wheat and barley. The strain can be readily transformed and is closely related to strain GZ3639 (NRRL 29169) that has been studied for trichothecene biosynthesis (Brown et al., 2001) and strain 00-676 (NRRL 34097) used as one parent with PH-1 for the genetic map (Gale et al., 2005).
Fusarium verticillioides
Fusarium verticillioides is the causal agent of kernel and ear rot of maize. This destructive disease occurs virtually everywhere that maize is grown worldwide. In years with high temperatures, drought, and heavy insect damage, the disease can significantly diminish crop quality.
The most significant economic impact of F. verticillioides is its ability to produce fumonisin mycotoxins. Various diseases caused by fumonisins have been reported in animals, such as liver and kidney cancer as well as neural tube defects in rodents (Howard et al. 2001, Seefelder et al. 2003), leukoencephalomalacia in equines (Wilson et al. 1992), and pulmonary edema in pigs (Kriek et al. 1981). More importantly, epidemiological correlations have been established between human esophageal cancer and the consumption of fumonisin-contaminated maize in some regions of the world where maize is a dietary staple. In addition, fumonisins have been reported to be a potential cause of neural tube defects in humans (Seefelder et al. 2003). Due to potential health risks, guidelines for fumonisin levels in food have been established by the US FDA and by other government agencies worldwide (FDA/CFSAN, 2001). In 2003, fumonisin B1, the fumonisin produced most abundantly by F. verticillioides, was added to the California Proposition 65 List of Substances Known to Cause Cancer.
Sequenced strain information: Strain 7600 (FRC M3125=NRRL 20956), which has been used extensively in molecular and pathological studies, was selected for the genome project. This strain is available at FGSC, NCAUR-ARS-USDA and the Fusarium Research Center at Penn State. The genome size is estimated to be 46 Mb with 12 chromosomes.
Fusarium oxysporum
Members of the Fusarium oxysporum species complex (FOSC) are the most common phytopathogenic Fusaria. They cause vascular wilts of over 100 cultivated plant species, including tomato, potato, sugarcane, bean, cowpea, date and oil palm, as well as cooking and dessert bananas (Beckman 1987, Moore et al. 2001). Tomato wilt, caused by F. oxysporum f. sp. lycopersici, has been reported in at least 32 countries worldwide (Jones et al., 1991). While plant disease resistance genes have been identified for the effective control of tomato wilt, new races of the pathogen continue to develop, overcoming deployed resistance and thwarting tomato breeding efforts (Cai et al., 2003; Gale et al., 2003). Because it is a long-lived, soil-borne pathogen, infested soil remains contaminated indefinitely, so only resistant varieties can be grown on that site. Sequenced strain information:Fusarium oxysporum f. sp. lycopersici strain 4287 (race 2, VCG 0030) was selected for sequencing. The strain is available from the Fungal Genetics Stock Center (FGSC 4286) and NCAUR/USDA (NRRL 34936). The genome size is estimated to be 59.9 Mb.
This strain was originally isolated from an infected tomato plant. In addition to tomato, it also infects Arabidopsis thaliana where it induces typical wilt symptoms. This characteristic permits extensive investigation of host-pathogen interactions, pathogen infection, and plant defense mechanisms, using the model plant system A. thaliana. Based on intensive study over the past 10 years, this strain has displayed remarkable phenotypic stability, including mycelial growth on different culture media, sporulation and high virulence. This strain is also highly amenable to transformation, via both protoplasts and Agrobacterium tumefaciens, and transformation-mediated gene disruption (Di Pietro et al., 2003). A mitotic linkage map was created from the protoplast fusion of two strains of F. oxysporum f. sp. lycopersici, VCG 0030 (Teunissen et al. 2003). A novel and highly efficient gene knock-out technique and molecular cytological tools also have been developed (Khang et al. 2005).