FUM gene expression and variation in fumonisin production of clonal isolates ofFusarium verticillioides MRC 826

Abstract

B-series fumonisins (FBs) are a family of carcinogenic mycotoxins that commonly occur in maize. These mycotoxins cause multiple diseases in animals and are epidemiologically associated with several human diseases in populations for which maize is a dietary staple. FBs are produced by multiple genera of the fungiAspergillus,Fusarium andTolypocladium, but the plant pathogenFusarium verticillioides is considered the primary cause of FB contamination in maize. OneF. verticillioides strain, MRC 826, is reported to produce high levels of FBs. However, in the current study, 18 isolates derived from strain MRC 826 exhibited highly variable levels of FB, which negatively correlated (r=-0.333;P<0.008) with fungal growth. Microsatellite analysis confirmed that all MRC 826 derived isolates examined were clonal, and 100% DNA sequence identity was observed across theFUM gene clusters of two high FB producing and two low FB producing isolates. At the gene expression level, qRT-PCR at each time point (7, 14, 21 and 28 days of incubation) showed differential upregulation of selectedFUM genes in the high compared to the low FB isolates. Variation in FB production appears due to differences inFUM gene expression, most likely caused by sequence differences at unexamined loci not part of theFUM cluster or from epigenetic influences. Clarification of the genetic/epigenetic basis for quantitative differences in fumonisin production among strains and isolates ofF. verticillioides has potential to reveal targets for reducing FB contamination in maize.