Abstract
In filamentous fungi, several lines of experimental evidence indicate that secondary metabolism is triggered by oxidative stress; however, the functional and molecular mechanisms that mediate this association are unclear. The basic leucine zipper (bZIP) transcription factor AtfB, a member of the bZIP/CREB family, helps regulate conidial tolerance to oxidative stress. In this work, we investigated the role of AtfB in the connection between oxidative stress response and secondary metabolism in the filamentous fungus Aspergillus parasiticus. This well characterized model organism synthesizes the secondary metabolite and carcinogen aflatoxin. Chromatin immunoprecipitation with specific anti-AtfB demonstrated AtfB binding at promoters of seven genes in the aflatoxin gene cluster that carry CREs. Promoters lacking CREs did not show AtfB binding. The binding of AtfB to the promoters occurred under aflatoxin-inducing but not under aflatoxin-noninducing conditions and correlated with activation of transcription of the aflatoxin genes. Deletion of veA, a global regulator of secondary metabolism and development, nearly eliminated this binding. Electrophoretic mobility shift analysis demonstrated that AtfB binds to the nor-1 (an early aflatoxin gene) promoter at a composite regulatory element that consists of highly similar, adjacent CRE1 and AP-1-like binding sites. The five nucleotides immediately upstream from CRE1, AGCC(G/C), are highly conserved in five aflatoxin promoters that demonstrate AtfB binding. We propose that AtfB is a key player in the regulatory circuit that integrates secondary metabolism and cellular response to oxidative stress.
Highlights
Cellular response to oxidative stress in vertebrates, plants, and fungi is of fundamental importance; it enables the cell to survive a variety of extra- and intracellular oxidative stressors
Cloning of AtfB from A. parasiticus—Previous Electrophoretic mobility shift analysis (EMSA) and Southwestern blot analysis indicated that a 32-kDa A. parasiticus protein is a key component in a protein complex that binds a cAMP-response element (CRE1) in the nor-1 promoter in vivo and in vitro
The deduced protein consists of 318 amino acids with a mass of 35.9 kDa, similar to the predicted molecular mass for the p32 we identified in previous work
Summary
Cellular response to oxidative stress in vertebrates, plants, and fungi is of fundamental importance; it enables the cell to survive a variety of extra- and intracellular oxidative stressors. As a part of the response to oxidative stress, transcription factors activated directly or indirectly by ROS bind to the promoters of specific genes that trigger defense and signaling related activities. Genetic and biochemical studies shed light on the role of ROS in fungal defense, pathogenicity, and development and suggest that fungi use similar stress response pathways as mammalian and plant cells (20 –24). AtfB Binds to Aflatoxin Gene Promoters toxin biosynthesis suggesting that oxidative stress serves as a trigger of secondary metabolism [26, 27, 32,33,34,35,36]. The molecular mechanisms that connect secondary metabolism, oxidative stress, and development are not clear
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
