Abstract
The RNA polymerase II (Pol II) transcription process is coordinated by the reversible phosphorylation of its largest subunit-carboxy terminal domain (CTD). Ssu72 is identified as a CTD phosphatase with specificity for phosphorylation of Ser5 and Ser7 and plays critical roles in regulation of transcription cycle in eukaryotes. However, the biofunction of Ssu72 is still unknown in Aspergillus flavus, which is a plant pathogenic fungus and produces one of the most toxic mycotoxins-aflatoxin. Here, we identified a putative phosphatase Ssu72 and investigated the function of Ssu72 in A. flavus. Deletion of ssu72 resulted in severe defects in vegetative growth, conidiation and sclerotia formation. Additionally, we found that phosphatase Ssu72 positively regulates aflatoxin production through regulating expression of aflatoxin biosynthesis cluster genes. Notably, seeds infection assays indicated that phosphatase Ssu72 is crucial for pathogenicity of A. flavus. Furthermore, the Δssu72 mutant exhibited more sensitivity to osmotic and oxidative stresses. Taken together, our study suggests that the putative phosphatase Ssu72 is involved in fungal development, aflatoxin production and pathogenicity in A. flavus, and may provide a novel strategy to prevent the contamination of this pathogenic fungus.
Highlights
IntroductionAspergillus flavus is a saprophytic plant pathogenic fungus that infects a range of seed crops (maize, peanuts, cottonseed and tree nuts) before and after harvest [1,2]
Aspergillus flavus is a saprophytic plant pathogenic fungus that infects a range of seed crops before and after harvest [1,2]
To identify the ortholog of Ssu72 phosphatase in A. flavus, the Ssu72 protein sequence of model organism S. cerevisiae was used to search with a basic local alignment search tool (BLAST) in the A. flavus genome database
Summary
Aspergillus flavus is a saprophytic plant pathogenic fungus that infects a range of seed crops (maize, peanuts, cottonseed and tree nuts) before and after harvest [1,2]. A. flavus is a human opportunistic pathogen, causing invasive aspergillosis in mammals and humans [3,4]. It is essential to explain and clarify the regulatory mechanism of this fungus in pathogenicity and aflatoxin biosynthesis. Previous studies have shown that aflatoxin biosynthesis and pathogenicity of A. flavus are regulated by multiple factors, such as temperature [9], water activity [10] and post-translational modifications (PTMs) including phosphorylation [11], acetylation [12], succinylation [13], methylation [14] and Toxins 2020, 12, 717; doi:10.3390/toxins12110717 www.mdpi.com/journal/toxins
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