|Chang, Perng Kuang|
Submitted to: Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2004
Publication Date: 12/1/2004
Citation: Wilson, R.A., Calvo, A.M., Chang, P.-K., Keller, N.P. 2004. Characterization of the Aspergillus parasiticus delta 12-desaturase gene: A role for lipid metabolism in the aspergillus-seed interaction. Microbiology. 150:2881-2888. Interpretive Summary: The contamination of oilseed crops by aflatoxigenic fungi remains a persistent problem in many countries. Hot and dry conditions promote infiltration of the oilseed host by Aspergillus flavus and A. parasiticus. The inoculum for fungal infection of the crop can be in the form of sclerotia, compact aggregates of fungal hyphae, or wind blown conidia. Following infection, the inoculum germinates, leading to fungal growth, aflatoxin production, and sporulation resulting in secondary infection. One approach to controlling the contamination of crops would involve reducing sporulation such that fewer spores are produced for the next round of the infection cycle. This requires an understanding of the factors that influence fungal development. Unsaturated fatty acids are important constituents of all cell membranes and are required for normal growth. In the Aspergillus spp., unsaturated fatty acids and their derivatives also influence sporulation processes. To investigate the relationship between fatty acid metabolism and fungal development, we have disrupted a gene in A. parasiticus necessary for fatty acid metabolism. We show that, compared to wild type, altering fatty acid biosynthesis by disrupting this gene delays germination of conidiospores, reduces growth and conidiation, and abolishes sclerotial development. Moreover, the A. parasiticus mutant strain is compromised in its ability to infect peanut and corn seed. This work might lead to a strategy that reduces inocula of aflatoxigenic strains in the field through the manipulation of fungal fatty acid metabolism. This would lead to a net reduction in aflatoxin contamination of oilseed crops during growing seasons, and a net increase in profitability to the growers.
Technical Abstract: In the mycotoxigenic oilseed pathogens Aspergillus flavus and Aspergillus parasiticus, and the model filamentous fungus Aspergillus nidulans, unsaturated fatty acids and their derivatives act as important developmental signals that affect asexual conidiospore, sexual ascospore, and/or sclerotial development. To dissect the relationship between lipid metabolism and fungal development, we generated an A. parasiticus delta 12-desaturase mutant unable to convert oleic acid to linoleic acid and thus impaired in polyunsaturated fatty acid biosynthesis. The delta 12-desaturase mutant demonstrates delayed spore germination, a two-fold reduction in growth, a reduced level of conidiation, and complete loss of sclerotial development compared to wild type. Host colonization is impaired as reflected by a decrease in conidial production on live peanut and corn seed by the mutant compared to the wild type. Similarly, the previously isolated A. nidulans delta 12-desaturase mutant has reduced colonization capabilities compared to wild type. Therefore, desaturation mutants display a key requisite affording a genetic solution to oilseed crop contamination by mycotoxigenic Aspergillus spp: a reduction in the production of conidia, the infectious particle of the pathogenic Aspergilli.