The transcriptional regulator Hbx1 affects the expression of thousands of genes in the aflatoxin-producing fungus Aspergillus flavus

Authors: Cary, Jeffrey; ENTWISTLE, SARAH - Northern Illinois University; SATTERLEE, TIM - Northern Illinois University; Mack, Brian; Gilbert, Matthew; Chang, Perng Kuang; Scharfenstein, Leslie; YIN, YANBIN - Northern Illinois University; CALVO, ANA - Northern Illinois University

Submitted to: G3, Genes/Genomes/Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2018
Publication Date: 1/1/2019
Citation: Cary, J.W., Entwistle, S., Satterlee, T., Mack, B.M., Gilbert, M.K., Chang, P.-K., Scharfenstein, L.L., Yin, Y., Calvo, A. 2019. The transcriptional regulator Hbx1 affects the expression of thousands of genes in the aflatoxin-producing fungus Aspergillus flavus. G3, Genes/Genomes/Genetics. 9(1):167-178. https://doi.org/10.1534/g3.118.200870.
DOI: https://doi.org/10.1534/g3.118.200870

Interpretive Summary: This work describes experiments that have been conducted in an effort to better understand the genetic mechanisms that control aflatoxin production and growth and development in Aspergillus flavus. Aflatoxins are toxic and carcinogenic compounds often produced by the fungi, A. flavus during growth on crops such as corn, peanuts, cottonseed, and treenuts. Because of the potential health risks, aflatoxin contamination of food and feed crops is also of great economic importance to farmers who cannot sell their crops due to strict domestic and international regulatory guidelines with regards to aflatoxin contamination. We have succeeded identifying a gene, designated hbx1, from A. flavus that when inactivated stops the fungus from making aflatoxins and also structures known as conidia and sclerotia that help the fungus to spread and survive in the field under adverse conditions. The hbx1 gene is a class of genes known as homeobox transcription factors that are known to regulate development in fungi, animals and humans. This study showed that hbx1 controls the expression of thousands of genes in A. flavus with a diversity of functions. These results further our knowledge of the role that hbx1 plays in regulating the biology of the fungus and this in turn will help in devising strategies for eliminating fungal toxin contamination of food and feed crops.

Technical Abstract: In filamentous fungi, homeobox proteins are conserved transcription factors described to control conidiogenesis and fruiting body formation. Eight homeobox (hbx) genes are found in the genome of the aflatoxin-producing ascomycete, Aspergillus flavus. While loss-of-function of seven of the eight genes had little to no effect on fungal growth and development, disruption of hbx1, resulted in aconidial colonies and lack of sclerotial production. Furthermore, the hbx1 mutant was unable to produce aflatoxins B1 and B2, cyclopiazonic acid and aflatrem. In the present study, hbx1 transcriptome analysis revealed that hbx1 has a broad effect on the A. flavus genome, and that its effect increases overtime, affecting more than six thousand genes (including over one thousand long non-coding RN A genes). Among them, the category of secondary metabolism (SM) genes, followed by that of carbohydrate metabolism, were the most affected. Specifically, regarding its effect on SM, we found that genes in forty four SM gene clusters where upregulated while forty nine where downregulated in the absence of hbx1, including the genes in the SM clusters responsible for the synthesis of asparasone, piperazine and aflavarin, all known to be associated with sclerotia. In addition, our study revealed that hbx1 affects the expression of other transcription factor genes involved in development, including the conidiation central regulatory pathway, flb genes and light-sensing genes.