Adenylate Cyclase AcyA Regulates Development, Aflatoxin Biosynthesis and Fungal Virulence in Aspergillus flavus.

Kunlong Yang,Limei Zhang,Shihua Wang,Chihao Chen,Yinghang Liu,Linlin Liang,Qiuping Qin,Feng Zhang,Huahui Lan,Yunchao You

doi:10.3389/fcimb.2016.00190

Abstract

Aspergillus flavus is one of the most important opportunistic pathogens of crops and animals. The carcinogenic mycotoxin, aflatoxins produced by this pathogen cause a health problem to human and animals. Since cyclic AMP signaling controls a range of physiological processes, like fungal development and infection when responding to extracellular stimuli in fungal pathogens, in this study, we investigated the function of adenylate cyclase, a core component of cAMP signaling, in aflatoxins biosynthesis and virulence on plant seeds in A. flavus. A gene replacement strategy was used to generate the deletion mutant of acyA that encodes the adenylate cyclase. Severe defects in fungal growth, sporulation and sclerotia formation were observed in the acyA deletion mutant. The defect in radical growth could be partially rescued by exogenous cAMP analog. The acyA mutant was also significantly reduced in aflatoxins production and virulence. Similar to the former studies in other fungi, The acyA mutant showed enhancing tolerance to oxidative stress, but more sensitive to heat stress. Overall, the pleiotropic defects of the acyA deletion mutant indicates that the cAMP-PKA pathway is involved in fungal development, aflatoxins biosynthesis and plant seed invasion in A. flavus.

Highlights

Aspergillus flavus is a saprophytic soilborne fungus that contaminates food-stuffs and a broad range of important agricultural crops, including maize, peanut, and cottonseed, with the most carcinogenic metabolite, aflatoxins (AFs) (Amaike and Keller, 2011; Yang et al, 2015)
The results showed that sclerotia formation in acyA mutant was severely blocked compared to that in wild type and acyAC strain (Figures 5A,B), indicating that AcyA is required for the formation of sclerotia in A. flavus
The qRT-PCR was performed to detect the transcript levels of laeA, encoding a global regulator of many secondary metabolisms, the aflatoxin globally regulated gene aflR, and the structure genes, aflD and aflO, and the resluts showed that the expression levels of laeA, aflR and aflO were significantly decreased in the acyA mutant compared to that in WT and acyA-C (Figure 9C), the aflD transcript showed no difference among these strains (Figure 9C). All these results indicated that the AcyA might play an important role in regulating aflatoxins biosynthesis by reducing the AF regulator genes’ expression in A. flavus

Summary

Introduction

Aspergillus flavus is a saprophytic soilborne fungus that contaminates food-stuffs and a broad range of important agricultural crops, including maize, peanut, and cottonseed, with the most carcinogenic metabolite, aflatoxins (AFs) (Amaike and Keller, 2011; Yang et al, 2015). This fungus is one of the most opportunistic pathogen of human and animals causing aspergillosis diseases or liver cancer either through consumption of contaminated food or through invasive growth (Hedayati et al, 2007; Amaike and Keller, 2011; Yang et al, 2015).

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