Functional Characterization Of Metacaspase Genes In Fusarium Graminearum

The ascomycete Fusarium graminearum causes a destructive disease of wheat,barley and other plants,known as Fusarium head blight(FHB).FHB not only causes serious yield losses but also produces trichothecene mycotoxins during infection,which have negative health impacts for humans and livestock.Deoxynivalenol(DON)is one of the most abundant trichothecenes and is a demonstrated virulence factor in plant infection.Disease control options are limited to using varieties of wheat that are partially resistant to F.graminearum and fungicides with incomplete effectiveness.Apoptosis,as a common form of programmed cell death(PCD),is an important physiological process.Metacaspase is an important cysteine-dependent protease that plays a critical role in programmed cell death in eukaryotic cells.However,there is no reports about its roles in F.graminearum.Through searching in NCBI and based on the differences of the protein structures,two FgMCAs were found in the F.graminearum genome.Phylogenetic analysis and domain comparisons revealed that the F.graminearum has two metacaspases belong to the metacaspase type I class.Both proteins contain P20 and P10 domains.The FgMCA1 and FgMCA2 gene replacement constructs were generated by the split-marker approach.Deletion of FgMCA1 and FgMCA2 decreased hyphal growth and conidiation.Inoculation experiments on wheat and corn silks revealed that the two mutants decrease pathogenicity significantly.The Fg MCA deletion mutants showed reduced deoxynivalenol(DON)production and expression of TRI gene compared with wide-type.The FgMCA deletion mutants showed increased tolerance to H2O2 on the CM medium.The two mutants showed decreased apoptosis rates in response to H2O2 treatment compared with the wild type.Both FgMCA1 and FgMCA2 localize to the cytoplasm.Taken together,the genome of F.graminearum contains two metacaspase genes,and phenotype analyses indicated that the two metacaspase genes are involved in hyphal growth,conidiation,DON content,and pathogenicity.The two mutants increased the tolerance to H2O2 and decreased the apoptosis rate under the H2O2 stress.