ARS | Publication request: ESTs Provide Unique Insight to Fumonisin Regulatory Gene FUM21

Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Abstract
Publication Acceptance Date: October 16, 2006
Publication Date: October 16, 2006
Citation: Brown, D.W., Butchko, R.A., Busman, M., Proctor, R. 2006. ESTs provide unique insight to fumonisin regulatory gene fum21 [abstract]. Aflatoxin Elimination Workshop. p. 42.

Technical Abstract: Fungal toxins are natural products that can negatively affect animal and plant health. Fungal genes involved in toxin synthesis are often located adjacent to each other within the genome (i.e., clustered) and encode structural enzymes, regulatory proteins, and/or proteins that provide self protection. Fumonisins are toxins synthesized by Fusarium species that may contaminate maize or maize products, are associated with several animal diseases, and are linked with cancer in animals and humans. The current fumonisin biosynthetic gene cluster includes 16 genes, of which none appear to play a regulatory role. We identified a new gene, based on analysis of Expressed Sequence Tags (ESTs), located adjacent to the fumonisin polyketide synthase gene, FUM1. The predicted protein of the new gene includes a Zn(II)2Cys6 DNA binding domain and a second domain also associated with fungal transcription factors. Gene deletion mutants ('fum21) produce no fumonisin after 10 days, and some fumonisin after 21 days growth on cracked maize, and accumulate significantly less FUM1 and FUM8 transcripts than wild type in a liquid medium. Over-expression of the gene in a 'fum21 mutant restored fumonisin biosynthesis. Based on these observations, we designate this new gene FUM21. Analysis of FUM21 ESTs identified an unusually large number of alternative splice forms (ASFs) where one or more introns had not been excised or, in the case of the 1st intron, an alternative 3¿ border maybe utilized. In all ASFs, a stop codon is introduced into the FUM21 ORF. To explore whether FUM21 ASFs play a role in fumonisin biosynthesis, microarray analysis of some FUM21 ASFs were conducted. We found that the expression of ASFs that retain the 7th intron increase over time, ASFs that retain the 2nd intron decrease over time, and ASFs that retain the 3rd or 4th intron do not appear to change significantly. We present a model depicting how ASFs may be involved in fumonisin biosynthesis.