Corepressors SsnF and RcoA Regulate Development and Aflatoxin B1 Biosynthesis in Aspergillus flavus NRRL 3357

Abstract

Aspergillus flavus is a saprophytic fungus that can be found across the entire world. It can produce aflatoxin B1 (AFB1), which threatens human health. CreA, as the central factor in carbon catabolite repression (CCR), regulates carbon catabolism and AFB1 biosynthesis in A. flavus. Additionally, SsnF-RcoA are recognized as the corepressors of CreA in CCR. In this study, ssnF and rcoA not only regulated the expressions of CCR factors and hydrolase genes, but also positively affected mycelia growth, conidia production, sclerotia formation, and osmotic stress response in A. flavus. More importantly, SsnF and RcoA were identified as positive regulators for AFB1 biosynthesis, as they modulate the AF cluster genes and the relevant regulators at a transcriptional level. Additionally, the interactions of SsnF-CreA and RcoA-CreA were strong and moderate, respectively. However, the interaction of SsnF and RcoA was weak. The interaction models of CreA-SsnF, CreA-RcoA, and SsnF-RcoA were also simulated with a docking analysis. All things considered, SsnF and RcoA are not just the critical regulators of the CCR pathway, but the global regulators involving in morphological development and AFB1 biosynthesis in A. flavus.

Implications of carbon catabolite repression for Aspergillus‐based cell factories: A review

“…[ 128 ] Recent studies have also found that in addition to CreA, SsnF, and RcoA, which are closely related to CreA in the CCR system, also affect aflatoxin production. [ 103 ] Although deletion of ssnF and rcoA had less effect on aflatoxin than deletion of creA , they still significantly reduced aflatoxin production. Compared with the wild type, the aflatoxin content of these two knockout strains was reduced by 3‐ and 7‐fold, respectively.…”

“…[ 103 ] Subsequent studies have shown that SsnF and RcoA not only regulate the expression of CCR related factors and hydrolase genes, but also positively affect conidial production and mycelial growth as global regulators. [ 103 ] For instance, in the ssnF deletion strains, the expression of amylase and xylanase genes was significantly reduced, meanwhile, the expression of CCR‐related genes, such as creA , creB , creC , creD , hulA , and schA , was also lower. [ 103 ] This study also found that the deletion of rcoA gene resulted in significant up‐regulation of the creC and creB genes, and significant down‐regulation of creD .…”

“…[ 103 ] For instance, in the ssnF deletion strains, the expression of amylase and xylanase genes was significantly reduced, meanwhile, the expression of CCR‐related genes, such as creA , creB , creC , creD , hulA , and schA , was also lower. [ 103 ] This study also found that the deletion of rcoA gene resulted in significant up‐regulation of the creC and creB genes, and significant down‐regulation of creD . [ 103 ] This suggests that RcoA can act as a positive regulator for creD , the same as SsnF, but simultaneously inhibit the expression of creC and creB genes.…”

“…Curiously, the effects of RcoA on hydrolase genes were not found to be consistent with SsnF. [ 103 ] Deletion of rcoA gene only reduced the expression of xlnA and cbhA , while all CCR pathway genes were significantly down‐regulated in the ssnF deleting strain, including those specific regulators (such as amyR and xlnR , etc.) and other hydrolase genes (such as amyA , cbhA , xlnA , eglA , eglC , etc.).…”

“…[ 102 ] A recent study in A. flavus has shown that the action of SsnF‐RcoA complex is biased towards independence, that is, the interactions of SsnF‐CreA and RcoA‐CreA are stronger than that of SsnF‐RcoA. [ 103 ] Subsequent studies have shown that SsnF and RcoA not only regulate the expression of CCR related factors and hydrolase genes, but also positively affect conidial production and mycelial growth as global regulators. [ 103 ] For instance, in the ssnF deletion strains, the expression of amylase and xylanase genes was significantly reduced, meanwhile, the expression of CCR‐related genes, such as creA , creB , creC , creD , hulA , and schA , was also lower.…”