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Association of aflatoxin biosynthesis and sclerotial development in Aspergillus parasiticus
Perng-Kuang Chang1, Joan W Bennett, Peter J Cotty
1Southern Regional Research Center, Agricultural Research Service, US Department of Agriculture, New Orleans, Louisiana 70124, USA. pkchang@srrc.ars.usda.gov
Abstract:
Secondary metabolism in fungi is frequently associated with asexual and sexual development. Aspergillus parasiticus produces aflatoxins known to contaminate a variety of agricultural commodities. This strictly mitotic fungus. besides producing conidia asexually, produces sclerotia, structures resistant to harsh conditions and for propagation. Sclerotia are considered to be derived from the sexual structure, cleistothecia. and may represent a vestige of ascospore production. Introduction of the aflatoxin pathway-specific regulatory gene, aflR, and aflJ, which encoded a putative co-activator, into an O-methylsterigmatocystin (OMST)-accumulating strain, A. parasiticus SRRC 2043, resulted in elevated levels of accumulation of major aflatoxin precursors, including norsolorinic acid (NOR), averantin (AVN), versicolorin A (VERA) and OMST. The total amount of these aflatoxin precursors, NOR, VERA, AVN and OMST, produced by the aflR plus aflJ transformants was two to three-fold that produced by the aflR transformants. This increase indicated a synergistic effect of aflR and aflJ on the synthesis of aflatoxin precursors. Increased production of the aflatoxin precursors was associated with progressive decrease in sclerotial size, alteration in sclerotial shape and weakening in the sclerotial structure of the transformants. The results showed that sclerotial development and aflatoxin biosynthesis are closely related. We proposed that competition for a common substrate, such as acetate, by the aflatoxin biosynthetic pathway could adversely affect sclerotial development in A. parasiticus.
Insights
Aflatoxin biosynthesis in Aspergillus parasiticus is linked to fungal development. Overexpression of aflatoxin genes aflR and aflJ enhances precursor production but impairs sclerotia formation, suggesting substrate competition.
Area of Science:
- Mycology
- Biochemistry
- Fungal Genetics
Background:
- Secondary metabolism in fungi, including aflatoxin production by Aspergillus parasiticus, is linked to developmental processes.
- Aspergillus parasiticus, a fungus known for aflatoxin contamination, also produces sclerotia, resistant structures potentially linked to sexual reproduction.
Purpose of the Study:
- To investigate the relationship between aflatoxin biosynthesis and sclerotial development in Aspergillus parasiticus.
- To examine the synergistic effect of aflatoxin pathway genes aflR and aflJ on aflatoxin precursor accumulation.
Main Methods:
- Genetic transformation of an O-methylsterigmatocystin (OMST)-accumulating strain (A. parasiticus SRRC 2043) with aflR and aflJ.
- Quantification of aflatoxin precursors (norsolorinic acid, averantin, versicolorin A, OMST).
- Assessment of sclerotial morphology and structure in transformants.
Main Results:
- Co-expression of aflR and aflJ led to a two-to-three-fold increase in aflatoxin precursor accumulation compared to aflR alone, indicating synergy.
- Increased aflatoxin precursor production correlated with reduced sclerotial size, altered shape, and weakened structure.
- Aflatoxin biosynthesis and sclerotial development were found to be closely related.
Conclusions:
- Aflatoxin biosynthesis and sclerotial development in A. parasiticus are interconnected processes.
- Competition for common substrates, such as acetate, between aflatoxin synthesis and sclerotial development pathways may explain the observed inverse relationship.