Food and Feed Safety Research Unit, USDA/ARS, Southern Regional Research Center, New Orleans, LA 70124, USA.
Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, Columbia, SC 29208, USA.
Toxins (Basel). 2017 Oct 12;9(10):315. doi: 10.3390/toxins9100315.
Homeobox proteins, a class of well conserved transcription factors, regulate the expression of targeted genes, especially those involved in development. In filamentous fungi, homeobox genes are required for normal conidiogenesis and fruiting body formation. In the present study, we identified eight homeobox () genes in the aflatoxin-producing ascomycete, , and determined their respective role in growth, conidiation and sclerotial production. Disruption of seven of the eight genes had little to no effect on fungal growth and development. However, disruption of the homeobox gene AFLA_069100, designated as , in two morphologically different strains, CA14 and AF70, resulted in complete loss of production of conidia and sclerotia as well as aflatoxins B₁ and B₂, cyclopiazonic acid and aflatrem. Microscopic examination showed that the Δ mutants did not produce conidiophores. The inability of Δ mutants to produce conidia was related to downregulation of (bristle) and (abacus), regulatory genes for conidiophore development. These mutants also had significant downregulation of the aflatoxin pathway biosynthetic genes , , and the cluster-specific regulatory gene, . Our results demonstrate that not only plays a significant role in controlling development but is also critical for the production of secondary metabolites, such as aflatoxins.
同源盒蛋白是一类保守的转录因子，可调节靶基因的表达，尤其是那些与发育相关的基因。在丝状真菌中，同源盒基因对于正常的分生孢子发生和子实体形成是必需的。在本研究中，我们在产黄曲霉（Aspergillus flavus）中鉴定出了 8 个同源盒基因（），并确定了它们在生长、分生孢子形成和菌核产生中的各自作用。这 8 个基因中的 7 个基因的缺失对真菌的生长和发育几乎没有影响。然而，同源盒基因 AFLA_069100（命名为）在两个形态不同的菌株 CA14 和 AF70 中的缺失导致完全丧失了分生孢子和菌核以及黄曲霉 B₁和 B₂、环匹阿尼酸和黄曲霉毒素的产生。显微镜检查表明，Δ突变体不产生分生孢子梗。Δ突变体不能产生分生孢子与调控基因（bristle 和 abacus）的下调有关，该调控基因参与分生孢子梗的发育。这些突变体也显著下调了黄曲霉毒素生物合成基因（aflaD、aflaE 和 aflaC）和簇特异性调控基因（aflR）。我们的结果表明，不仅在控制发育方面起着重要作用，而且对次级代谢产物（如黄曲霉毒素）的产生也至关重要。
