Frequency of three mutations in the fumonisin biosynthetic gene cluster ofFusarium fujikuroi that are predicted to block fumonisin production

Abstract

Fusarium fujikuroi is the most prominent pathogen found in rice. In addition to gibberellin,F. fujikuroi produces various secondary metabolites, including the polyketide mycotoxins, fumonisins. Fumonisin production is conferred by the fumonisin biosynthetic gene (FUM) cluster consisting of 15-17 genes.F. fujikuroi is phylogenetically subclassified into one group with fumonisin production (F-group) and another group in which fumonisin production is undetectable (G-group). In a previous study, a G-to-T substitution (FUM21_G2551T) in theFUM cluster transcription factor gene,FUM21, was identified as a cause of fumonisin-non-production in a G-group strain. In the current study, further analysis of G-group strains identified two additional mutations that involvedFUM-cluster genes essential for fumonisin production: (1) a 22.4-kbp deletion in theFUM10-FUM19 region; and (2) a 1.4-kbp insertion inFUM6. PCR analysis of 44 G-group strains, indicated that 84% had the FUM21_G2551T mutation, 50% had the 22.4-kbpFUM10-FUM19 deletion, and 32% had the 1.4-kbp insertion inFUM6, and some strains had two or all the mutations. None of the mutations were detected in the 51 F-group strains examined. Each of the three mutations alone could account for the lack of fumonisin production in G-group strains. However, one G-group strain did not have any of the mutations. Therefore, another mutation(s) is likely responsible for the lack of fumonisin production in some G-group strains ofF. fujikuroi.