Overproduction of mycotoxin biosynthetic enzymes triggers Fusarium toxisome-shaped structure formation via endoplasmic reticulum remodeling

Abstract

Mycotoxin deoxynivalenol (DON) produced by the Fusarium graminearum complex is highly toxic to animal and human health. During DON synthesis, the endoplasmic reticulum (ER) of F. graminearum is intensively reorganized, from thin reticular structure to thickened spherical and crescent structure, which was referred to as “DON toxisome”. However, the underlying mechanism of how the ER is reorganized into toxisome remains unknown. In this study, we discovered that overproduction of ER-localized DON biosynthetic enzyme Tri4 or Tri1, or intrinsic ER-resident membrane proteins FgHmr1 and FgCnx was sufficient to induce toxisome-shaped structure (TSS) formation under non-toxin-inducing conditions. Moreover, heterologous overexpression of Tri1 and Tri4 proteins in non-DON-producing fungi F. oxysporum f. sp. lycopersici and F. fujikuroi also led to TSS formation. In addition, we found that the high osmolarity glycerol (HOG), but not the unfolded protein response (UPR) signaling pathway was involved in the assembly of ER into TSS. By using toxisome as a biomarker, we screened and identified a novel chemical which exhibited high inhibitory activity against toxisome formation and DON biosynthesis, and inhibited Fusarium growth species-specifically. Taken together, this study demonstrated that the essence of ER remodeling into toxisome structure is a response to the overproduction of ER-localized DON biosynthetic enzymes, providing a novel pathway for management of mycotoxin contamination.

Nucleoside Diphosphate Kinase FgNdpk Is Required for DON Production and Pathogenicity by Regulating the Growth and Toxisome Formation of Fusarium graminearum

“…DON is synthesized in specialized subcellular structures called toxisomes . The toxisomes are approximately 3 to 4 μm in diameter and were presumed to be the site for trichothecene biosynthesis, and may have developed from reorganized ER responsive to trichothecene induction. ,− The cytochrome P450 oxygenases FgTri1, FgTri4, and FgTri11 are involved in DON biosynthesis and are clustered and anchored to the smooth ER membrane of the toxisome, along with P450 reductase and HMG-CoA reductase in F. graminearum .…”

“…8−10 Two cytochrome P-450 oxygenases (FgTri1 and FgTri4) localize to spherical organelles, approximately 3 to 4 μm in diameter, that were presumed to be the site for trichothecene biosynthesis. 5,11,12 Subsequently, these spherical organelles were named toxisomes, derived from remodeled endoplasmic reticulum (ER) under mycotoxin-inducing conditions. 8,13 In recent years, myosin I, actin capping proteins, microtubule, plasma membrane H + -ATPase FgPMA1, venturicidin A, transcription factor FgStuA, and RNA exosome complex were demonstrated to be required for toxisome formation or assembly in F. graminearum.…”

“…Fusrarium graminearum is a plant pathogen that infects many crop plants, including wheat and barley, and causes Fusarium head blight. − The fungus produces many mycotoxins, including the trichothecenes deoxynivalenol (DON), nivalenol (NIV), and the estrogenic mycotoxin zearalenone . These mycotoxins contaminate grains and cause serious health problems in humans and animals. − In Fusarium species, the enzymes involved in the de novo trichothecene biosynthetic pathway (from acetyl-CoA to DON) have been comprehensively investigated. − Two cytochrome P-450 oxygenases (FgTri1 and FgTri4) localize to spherical organelles, approximately 3 to 4 μm in diameter, that were presumed to be the site for trichothecene biosynthesis. ,, Subsequently, these spherical organelles were named toxisomes, derived from remodeled endoplasmic reticulum (ER) under mycotoxin-inducing conditions. , In recent years, myosin I, actin capping proteins, microtubule, plasma membrane H + -ATPase FgPMA1, venturicidin A, transcription factor FgStuA, and RNA exosome complex were demonstrated to be required for toxisome formation or assembly in F. graminearum. ,− However, the mechanisms of the formation and assembly of the toxisomes are still not well characterized.…”