Development of sexual structures influences metabolomic and transcriptomic profiles in Aspergillus flavus

Authors: LUIS, JANE - North Carolina State University; CARBONE, IGNAZIO - North Carolina State University; Mack, Brian; Lebar, Matthew; Cary, Jeffrey; Gilbert, Matthew; Bhatnagar, Deepak; Carter-Wientjes, Carol; PAYNE, GARY - Retired Non ARS Employee; Moore, Geromy; AMEEN, YAKEN - North Carolina State University; OJIAMBO, PETER - North Carolina State University

Submitted to: Fungal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2022
Publication Date: 1/31/2022
Citation: Luis, J.M., Carbone, I., Mack, B.M., Lebar, M.D., Cary, J.W., Gilbert, M.K., Bhatnagar, D., Carter-Wientjes, C.H., Payne, G.A., Moore, G.G., Ameen, Y.O., Ojiambo, P.S. 2022. Development of sexual structures influences metabolomic and transcriptomic profiles in Aspergillus flavus. Fungal Biology. 126:187-200.

Interpretive Summary: Aflatoxins are toxic and carcinogenic compounds produced by a fungus during growth on oilseed crops such as corn and have been associated with adverse health risks following exposure to humans and livestock. The fungus can also directly infect livestock and humans with compromised immune systems. Aflatoxin contamination, thus, poses significant food safety and food security risk particularly in developing countries where these crops are important food crops and are a major contributor to the economy. Aflatoxin producing fungi such as Aspergillus flavus can reproduce sexually by formation of structures known as sclerotia that are fertilized by structures termed conidia. The mechanism by which conidia fertilize sclerotia is not well understood nor are the biosynthetic processes that take place once a sclerotium has been fertilized. We have identified the expression patterns of genes produced during the fertilization process as well as identified chemical compounds produced when sclerotia are fertilized. The study of genes and compounds produced during sexual reproduction will aid in better understanding the process of fertilization. This will be useful in developing strategies to control aflatoxin contamination through the design of improved biological control fungi that are incapable of sexual recombination thus reducing the chances of conversion of non-aflatoxin producing biocontrol strains to aflatoxin producing due to sexual recombination with native aflatoxin producing strains present in the field.

Technical Abstract: Sclerotium (female) fertility, the capability of a strain to produce ascocarps in which meiosis occurs, influences morphological changes within the sclerotia during sexual reproduction in Aspergillus flavus. Although sclerotial morphogenesis has been linked to biosynthesis of secondary metabolites (SMs), metabolic and transcriptomic changes that occur within the sclerotia during sexual development in A. flavus are not known. Four treatments consisting of sclerotia from high fertility cross (Hi-Fert), low fertility cross (Lo-Fert), unmated NRRL 29507, and unmated NRRL 21882 were grown on mixed cereal agar and incubated at 30°C in continuous dark. Samples were harvested immediately after crosses were made and every 2 weeks until 8 weeks of incubation then subjected to targeted metabolomics and transcriptomic analysis. Aflatoxin B1 (AFB1) exhibited varied expression patterns between Hi-Fert and unmated NRRL 29507, while AFB1 consistently remained low or undetected in Lo-Fert and NRRL 21882. SM profiling of 17 SMs showed the elevated production of hydroxyaflavazole, an indole diterpene isomer, and an aflavinine isomer in Hi-Fert at 4 to 8 weeks, which coincides with the formation of ascocarps, asci and ascospores in A. flavus. Similarly, transcriptional analysis identified high expression of ayg1, hxtA, MAT1, asd-3, preA, preB, and SM gene clusters 30 and 44 in Hi-Fert at these time-points. Genes involved in vegetative incompatibility were also investigated. Results of this study broaden our knowledge of the biochemical and transcriptional processes that occur during sexual development in A. flavus.