Microtubule-assisted mechanism for toxisome assembly in Fusarium graminearum

In Fusarium graminearum, a trichothecene biosynthetic complex known as the toxisome forms ovoid and spherical structures in the remodelled endoplasmic reticulum (ER) under mycotoxin-inducing conditions. Previous studies also demonstrated that disruption of actin and tubulin results in a significant decrease in deoxynivalenol (DON) biosynthesis in F. graminearum. However, the functional association between the toxisome and microtubule components has not been clearly defined. In this study we tested the hypothesis that the microtubule network provides key support for toxisome assembly and thus facilitates DON biosynthesis. Through fluorescent live cell imaging, knockout mutant generation, and protein-protein interaction assays, we determined that two of the four F. graminearum tubulins, alpha(1) and beta(2) tubulins, are indispensable for DON production. We also showed that these two tubulins are directly associated. When the alpha(1)-beta(2) tubulin heterodimer is disrupted, the metabolic activity of the toxisome is significantly suppressed, which leads to significant DON biosynthesis impairment. Similar phenotypic outcomes were shown when F. graminearum wild type was treated with carbendazim, a fungicide that binds to microtubules and disrupts spindle formation. Based on our results, we propose a model where alpha(1)-beta(2) tubulin heterodimer serves as the scaffold for functional toxisome assembly in F. graminearum.

Automated summary

In Fusarium graminearum, alpha(1) and beta(2) tubulins are essential for deoxynivalenol (DON) biosynthesis, with disruption of the alpha(1)-beta(2) tubulin heterodimer leading to impaired toxisome metabolic activity and decreased DON production. This study suggests that the alpha(1)-beta(2) tubulin heterodimer acts as the scaffold for functional toxisome assembly in F. graminearum.