SntB triggers the antioxidant pathways to regulate development and aflatoxin biosynthesis in Aspergillus flavus
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eLife assessment
In this useful study, the authors investigate the regulatory mechanisms related to toxin production and pathogenicity in Aspergillus flavus. Their observations indicate that the SntB protein regulates morphogenesis, aflatoxin biosynthesis, and the oxidative stress response, however, the data supporting these conclusions are incomplete. The work will be of interest to bacteriologists.
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Abstract
The epigenetic reader SntB was identified as an important transcriptional regulator of growth, development, and secondary metabolite synthesis in Aspergillus flavus . However, the underlying molecular mechanism is still unclear. In this study, sntB gene deletion (Δ sntB ), complementary (Com- sntB ), and HA tag fused to sntB ( sntB -HA) strains were constructed by using the homologous recombination method, respectively. Our results revealed that deletion of sntB inhibited the processes of mycelia growth, conidial production, sclerotia formation, aflatoxin synthesis, and ability to colonize host compared to wild type (WT), and the defective phenotype of knockout strain Δ sntB could be restored in its complementary strain Com- sntB . Chromatin immunoprecipitation sequencing (ChIP-seq) of sntB- HA and WT and RNA sequencing (RNA-seq) of Δ sntB and WT strains revealed that SntB played key roles in oxidative stress response of A. flavus . The function of catC (encode a catalase) gene was further analyzed based on the integration results of ChIP-seq and RNA-seq. In Δ sntB strain, the relative expression level of catC was significantly higher than in WT strain, while a secretory lipase encoding gene (G4B84_008359) was down-regulated. Under the stress of oxidant menadione sodium bisulfite (MSB), the deletion of sntB obvious down-regulated the expression level of catC . After deletion of catC gene, the mycelia growth, conidial production, and sclerotia formation were inhibited, while ROS level and aflatoxin production were increased compared to the WT strain. Results also showed that the inhibition rate of MSB to Δ catC strain was significantly lower than that of WT group and AFB1 yield of the Δ catC strain was significantly decreased than that of WT strain under the stress of MSB. Our study revealed the potential machinery that SntB regulated fungal morphogenesis, mycotoxin anabolism, and fungal virulence through the axle of from SntB to fungal virulence and mycotoxin bio-synthesis, i.e. H3K36me3 modification-SntB-Peroxisomes-Lipid hydrolysis-fungal virulence and mycotoxin bio-synthesis. The results of the study shed light into the SntB mediated transcript regulation pathway of fungal mycotoxin anabolism and virulence, which provided potential strategy for control the contamination of A. flavus and its aflatoxins.
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eLife assessment
In this useful study, the authors investigate the regulatory mechanisms related to toxin production and pathogenicity in Aspergillus flavus. Their observations indicate that the SntB protein regulates morphogenesis, aflatoxin biosynthesis, and the oxidative stress response, however, the data supporting these conclusions are incomplete. The work will be of interest to bacteriologists.
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Reviewer #1 (Public Review):
The manuscript by Wu et al. explores the role of the histone reader protein SntB in Aspergillus flavus, claiming it to be a key regulator of development and aflatoxin biosynthesis. While the study incorporates various techniques, including gene deletion, ChIP-seq, and RNA-seq, several concerns and omissions in the paper raise questions about the validity and completeness of the presented findings.
(1) Omissions of Prior Work:
The authors fail to acknowledge and integrate prior research by Pfannenstiel et al. (2018) on the sntB gene in A. flavus, which covered phenotypic changes, RNA-seq data, and histone modifications. This omission raises concerns about the transparency and completeness of the current study.The absence of reference to studies by Karahoda et al. (2022, 2023) revealing SntB's involvement in …
Reviewer #1 (Public Review):
The manuscript by Wu et al. explores the role of the histone reader protein SntB in Aspergillus flavus, claiming it to be a key regulator of development and aflatoxin biosynthesis. While the study incorporates various techniques, including gene deletion, ChIP-seq, and RNA-seq, several concerns and omissions in the paper raise questions about the validity and completeness of the presented findings.
(1) Omissions of Prior Work:
The authors fail to acknowledge and integrate prior research by Pfannenstiel et al. (2018) on the sntB gene in A. flavus, which covered phenotypic changes, RNA-seq data, and histone modifications. This omission raises concerns about the transparency and completeness of the current study.The absence of reference to studies by Karahoda et al. (2022, 2023) revealing SntB's involvement in the KERS complex in A. flavus and A. nidulans is a major oversight. This raises questions about the specificity of SntB's regulatory functions, as it may be part of a larger complex. The authors should clarify why these studies were omitted and how they ensure that SntB alone, and not the entire KERS complex, is responsible for the observed effects.
(2) Transparency and Accessibility of Data:
The lack of accessibility and visualization tools for ChIP-seq and RNA-seq data poses a challenge for independent verification and in-depth analysis. The authors should address this issue by providing more accessible data or explaining the limitations of data availability. A critical component missing from the paper is a detailed presentation of ChIP-seq data, specifically demonstrating SntB binding patterns on key promoters. This omission weakens the link between SntB and the mentioned regulatory genes. The authors should include these crucial data visualizations to strengthen their claims.(3) SntB Binding Sites and Consensus Sequence:
The study mentions several genes upregulated in the sntB mutant without demonstrating SntB binding sites on their promoters. A detailed analysis of SntB binding maps is necessary to establish a direct link between SntB and these regulatory genes.(4) Mechanistic Insight into Peroxisome Biogenesis:
If SntB indeed regulates peroxisome biogenesis, the absence of markers for peroxisomes and the localization of peroxisomes in the sntB mutant vs. WT strains is a significant gap. Providing evidence for peroxisome regulation is crucial for understanding the proposed mechanism and validating the study's claims.In summary, while the manuscript presents intriguing findings regarding SntB's role in A. flavus, the omissions of prior work, lack of transparency in data accessibility, and insufficient mechanistic insights call for revisions and additional experimental evidence to strengthen the validity and impact of the study. Addressing these concerns will enhance the manuscript's contribution to the field.
Additionally, the way the English language is used could be improved.
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Reviewer #2 (Public Review):
Summary:
This work is of great significance in revealing the regulatory mechanisms of pathogenic fungi in toxin production, pathogenicity, and in its prevention and pollution control. Overall, this is generally an excellent manuscript.Strengths:
The data in this manuscript is robust and the experiments conducted are appropriate.Weaknesses:
(1) The authors found that SntB played key roles in the oxidative stress response of A. flavus by ChIP-seq and RNA sequencing. To confirm the role of SntB in oxidative stress, the authors have to better measure the ROS levels in the ΔsntB and WT strains, besides the ΔcatC strain.(2) Why did the authors only study the function of catC among the 7 genes related to an oxidative response listed in Table S14?
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