FgLEU1 Is Involved in Leucine Biosynthesis, Sexual Reproduction, and Full Virulence in Fusarium graminearum .

Fusarium head blight (FHB) caused by Fusarium graminearum is a significant disease among cereal crops. In F. graminearum , biosynthesis of leucine, which is a branched chain amino acid, is achieved by converting α-isopropylmalate to β-isopropylmalate catalyzed by isopropylmalate isomerase encoded by LEU1 . Considering the potential for targeting this pathway by fungicides, we characterized the gene FgLEU1 (FGSG-09589) in the Fusarium graminearum genome using bioinformatics methods. For functional characterization, we constructed a deletion mutant of FgLEU1 (Δ LEU1 ) through homologous recombination. Compared with the wild-type strain PH-1, Δ LEU1 showed slower colony growth and fewer aerial mycelia. Leucine addition was needed to ensure proper mutant growth. Further, Δ LEU1 showed decreased conidial production and germination rates, and could not produce ascospores. Moreover, Δ LEU1 showed complete loss of pathogenicity and reduced ability to produce deoxynivalenol (DON) and aurofusarin. Upstream and downstream genes of FgLEU1 were significantly upregulated in Δ LEU1 . Contrary to previous reports, the deletion mutant was more resistant to osmotic stress and cell wall-damaging agents than the wild-type. Taken together, FgLEU1 plays a crucial role in leucine synthesis, aerial mycelial growth, sexual and asexual reproduction, pathogenicity, virulence, and pigmentation in Fusarium graminearum , indicating its potential as a target for novel antifungal agents.