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In this study we characterized FgIlv5, a homologue of the Saccharomyces cerevisiae keto-acid reductoisomerase (KARI) from the important wheat head scab fungus Fusarium graminearum. KARI is a key enzyme in the branched-chain amino acids (BCAAs, including leucine, isoleucine and valine) biosynthetic pathway which exists in a variety of organisms from bacteria to fungi and high plants, but not mammals. The FgILV5 deletion mutant ΔFgIlv5-4 failed to grow when the culture medium was nutritionally limited for BCAAs. When grown on PDA plates, ΔFgIlv5-4 exhibited a significant decrease in aerial hyphae formation and red pigmentation. Conidia formation was also blocked in ΔFgIlv5-4. Exogenous addition of 1 mM isoleucine and valine could rescue the defects of mycelial growth and conidial morphogenesis.Cellular stress assays showed that ΔFgIlv5-4 was more sensitive to osmotic and oxidative stresses. In addition, virulence of ΔFgIlv5-4 was dramatically reduced on wheat heads, and a low level of deoxynivalenol (DON) production was detected in ΔFgIlv5-4 in wheat kernels. Taken together, results of this study indicate that FgIlv5 is involved in valine and isoleucine biosynthesis and is required for full virulence in F. graminearum.
PMID: 24493249 [PubMed - as supplied by publisher]