Dongya Shi

Heme biosynthesis is a highly conserved pathway from bacteria to higher animals. Heme, which serves as a prosthetic group for various enzymes involved in multiple biochemical processes, is essential in almost all species, making heme homeostasis vital for life. However, studies on the biological functions of heme in filamentous fungi are scarce. In this study, we investigated the role of heme in Fusarium graminearum. A mutant lacking the rate-limiting enzymes in heme synthesis, coproporphyrinogen III oxidase (Cpo) or ferrochelatase (Fc), was constructed using a homologous recombination strategy. The results showed that the absence of these enzymes was lethal to F. graminearum, but the growth defect could be rescued by the addition of hemin, so we carried out further studies with the help of hemin. The results demonstrated that heme was required for the activity of FgCyp51, and its absence increased the sensitivity to tebuconazole and led to the upregulation of FgCYP51 in F. graminearum. Additionally, heme plays an indispensable role in the life cycle of F. graminearum, which is essential for vegetative growth, conidiation, external stress response (especially oxidative stress), lipid accumulation, fatty acid β-oxidation, autophagy, and virulence.

Smi1 is a protein required for cell cycle progression, morphogenesis, stress response and life span of Saccharomyces cerevisiae. FaSmi1 was identified as a Smi1 homolog in a wheat scab pathogenic fungus Fusarium asiaticum strain 2021. The deletion of FaSmi1 leads to defects in mycelial growth, asexual reproduction, and virulence. The FaSmi1 deletion mutant also exhibited increased sensitivity to osmotic stresses generated by NaCl and KCl, but increased tolerance to oxidative stresses and cell wall integrity inhibitors. All of these defects were restored by genetic complementation of the mutant with the whole parental FaSmi1 gene. Interestingly, the antioxidant system-associated genes exhibit a lower expression level and the mycotoxins’ DON content was decreased in the FaSmi1 deletion mutant compared with the parental strain 2021. These results indicate that FaSmi1 plays a critical role in the vegetative development, asexual reproduction, DON production and virulence of F. asiaticum.