Inhibition of plant-pathogenic fungi by a corn trypsin inhibitor overexpressed in Escherichia coli.
ABSTRACT The cDNA of a 14-kDa trypsin inhibitor (TI) from corn was subcloned into an Escherichia coli overexpression vector. The overexpressed TI was purified based on its insolubility in urea and then refolded into the active form in vitro. This recombinant TI inhibited both conidium germination and hyphal growth of all nine plant pathogenic fungi studied, including Aspergillus flavus, Aspergillus parasiticus, and Fusarium moniliforme. The calculated 50% inhibitory concentration of TI for conidium germination ranged from 70 to more than 300 microgram/ml, and that for fungal growth ranged from 33 to 124 microgram/ml depending on the fungal species. It also inhibited A. flavus and F. moniliforme simultaneously when they were tested together. The results suggest that the corn 14-kDa TI may function in host resistance against a variety of fungal pathogens of crops.
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ABSTRACT: Fumonisins (FB) are mycotoxins found in (italic)Fusarium verticillioides-infected maize grain worldwide. Attention has focused on FBs because of their widespread occurrence, acute toxicity to certain livestock, and their potential carcinogenicity. FBs are present at low levels in most field-grown maize but may spike to high levels depending on both the environment and genetics of the host plant. Among the strategies for reducing risk of FB contamination in maize supplied to the market, development and deployment of Fusarium ear mold-resistant maize germplasm is a high priority. Breeding for increased ear mold tolerance and reduced mycotoxin levels is being practiced today in both commercial and public programs, but the amount of resistance achievable may be limited due to complicated genetics and/or linkage to undesirable agronomic traits. Molecular markers can be employed to speed up the incorporation of chromosomal regions that have a quantitative effect on resistance (quantitative trait loci). Transgenic approaches to ear mold/mycotoxin resistance are now feasible as well. These potentially include genetically enhanced resistance to insect feeding, increased fungal resistance, and detoxification/prevention of mycotoxins in the grain. An example of the first of these approaches is already on the market, namely transgenic maize expressing Bacillus thuringiensis (Bt) toxin, targeted to the European corn borer. Some Bt maize hybrids have the potential to reduce FB levels in field-harvested grain, presumably through reduced feeding of Bt-susceptible insects in ear tissues. However, improved ear mold resistance per se is still an important goal, as the plant will still be vulnerable to noninsect routes of entry to (italic)Fusarium. A second approach, transgene-mediated control of the ability of Fusarium to infect and colonize the ear, could potentially be achieved through overexpression of specific antifungal proteins and metabolites, or enhancement of the plant's own defense systems in kernel tissues. This has not yet been accomplished in maize, although promising results have been obtained recently in other monocots versus other fungal and bacterial pathogens. Achieving reproducible and stable enhanced ear mold resistance under field conditions will be immensely challenging for biotechnologists. A third approach, transgene strategies aimed at preventing mycotoxin biosynthesis, or detoxifying mycotoxins in planta, could provide further protection for the grower in environments where FBs present a risk to the crop even when the maize is relatively resistant to Fusarium mold. In one example of such a strategy, enzymes that degrade FBs have been identified in a filamentous saprophytic fungus isolated from maize, and corresponding genes have been cloned and are currently being tested in transgenic maize.Environmental Health Perspectives 06/2001; 109 Suppl 2:337-42. · 7.04 Impact Factor
Article: Comparative study of the major Iranian cereal cultivars and some selected spices in relation to support Aspergillus parasiticus growth and aflatoxin production.[show abstract] [hide abstract]
ABSTRACT: Aflatoxins are toxic fungal metabolites enable to contaminate a wide range of natural substrates. This contamination can be host-specific for different plant species. In this study, the ability of a toxigenic Aspergillus parasiticus to produce various aflatoxins on major Iranian cereals was evaluated with special focus on plant susceptibility to toxin production at cultivar level. Aspergillus parasiticus cultured on major Iranian cereal cultivars and some selected spices was incubated in shaking condition at 28 masculineC for 6 days. The concentration of aflatoxins B1 and total (B1, B2, G1 and G2) was measured by thin layer chromatography. The amounts of aflatoxin B1 produced on maize, wheat and rice cultivars were in the ranges of 1.0-33.9, 41.9-193.7, and 39.1-82.3 microg/g fungal weight, respectively. Interestingly, genetically modified Bacillus thuringiensis rice (GM rice) of Tarom Molaii cultivar examined for the first time in this study showed less susceptibility to aflatoxin production in comparison with its normal counterpart (P less than 0.05). The mean of aflatoxin production on maize cultivars was less than both wheat and rice cultivars that indicates considerable resistance of maize to aflatoxin compared with two other cereals. Unlike to Cuminum cyminum, both Helianthus annuus and Carum carvi seeds were highly resistant to aflatoxin production. These results indicate that inter- and intra-species differences exist in susceptibility of the major Iranian cereals as well as spices tested to A. parasiticus growth and aflatoxin production. Further studies are recommended to determine resistance markers of selected cultivars of Iranian cereals.Iranian biomedical journal 11/2008; 12(4):229-36.