Aflatoxin biosynthesis is a novel source of reactive oxygen species--a potential redox signal to initiate resistance to oxidative stress?
Aflatoxin biosynthesis in the filamentous fungus Aspergillus parasiticus involves a minimum of 21 enzymes, encoded by genes located in a 70 kb gene cluster. For aflatoxin biosynthesis to be completed, the required enzymes must be transported to specialized early and late endosomes called aflatoxisomes. Of particular significance, seven aflatoxin biosynthetic enzymes are P450/monooxygenases which catalyze reactions that can produce reactive oxygen species (ROS) as byproducts. Thus, oxidative reactions in the aflatoxin biosynthetic pathway could potentially be an additional source of intracellular ROS. The present work explores the hypothesis that the aflatoxin biosynthetic pathway generates ROS (designated as "secondary" ROS) in endosomes and that secondary ROS possess a signaling function. We used specific dyes that stain ROS in live cells and demonstrated that intracellular ROS levels correlate with the levels of aflatoxin synthesized. Moreover, feeding protoplasts with precursors of aflatoxin resulted in the increase in ROS generation. These data support the hypothesis. Our findings also suggest that secondary ROS may fulfill, at least in part, an important mechanistic role in increased tolerance to oxidative stress in germinating spores (seven-hour germlings) and in regulation of fungal development.
Department of Food Science and Human Nutrition, Michigan State University (MSU), East Lansing, MI 48824, USA. roze@msu.edu.|Department of Plant Biology, Michigan State University (MSU), East Lansing, MI 48824, USA. roze@msu.edu.
Ludmila V
LV
Roze
Department of Microbiology and Molecular Genetics, Michigan State University (MSU), East Lansing, MI 48824, USA. laivenie@msu.edu.
Maris
M
Laivenieks
Department of Food Science and Human Nutrition, Michigan State University (MSU), East Lansing, MI 48824, USA. lunohong@yahoo.co.kr.
Sung-Yong
SY
Hong
Department of Food Science and Human Nutrition, Michigan State University (MSU), East Lansing, MI 48824, USA. weejosep@msu.edu.
Josephine
J
Wee
Department of Food Science and Human Nutrition, Michigan State University (MSU), East Lansing, MI 48824, USA. wongs94@yahoo.com.
Shu-Shyan
SS
Wong
Department of Food Science and Human Nutrition, Michigan State University (MSU), East Lansing, MI 48824, USA. vanosben@msu.edu.
Benjamin
B
Vanos
Department of Food Science and Human Nutrition, Michigan State University (MSU), East Lansing, MI 48824, USA. awaddeen@msu.edu.
Deena
D
Awad
Southern Regional Research Center, Agricultural Research Service, USDA, New Orleans, LA 70124, USA. ehrlich8@gmail.com.
Kenneth C
KC
Ehrlich
Department of Food Science and Human Nutrition, Michigan State University (MSU), East Lansing, MI 48824, USA. jlinz@msu.edu.|Department of Microbiology and Molecular Genetics, Michigan State University (MSU), East Lansing, MI 48824, USA. jlinz@msu.edu.|Center for Integrative Toxicology, Michigan State University (MSU), East Lansing, MI 48824, USA. jlinz@msu.edu.
John E
JE
Linz
D000348:Aflatoxins / Q000096:biosynthesis*; D001230:Aspergillus / Q000187:drug effects / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism
D000348:Aflatoxins; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D002374:Catalase; D013482:Superoxide Dismutase