Submitted to: Aflatoxin Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2003
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Fumonisins are a family of polyketide-derived mycotoxins produced by the maize pathogen Fusarium verticillioides. This fungus can be found growing endophytically in most, if not all maize fields in the U.S. But, under some conditions, it can cause disease at any stage of maize plant development including ear, root and stalk. In addition, fumonisins can be found in all qualities of maize; from exceptional to poor. Fumonisin ingestion is associated with several animal diseases and is epidemiologically associated with human esophageal cancer in some regions of the world. We are looking to limit maize crop losses, due to physical damage as well as the presence of fumonisins, by understanding toxin biosynthesis and pathogenesis. The identification of genes expressed under different fungal growth conditions have given scientists important clues to understand biological processes. We, in collaboration with The Institute for Genomic Research (TIGR), have sequenced the 5' ends of F. verticillioides cDNAs derived from seven different growth conditions. Growth conditions of three libraries were similar but differed in length of time (i.e. 24, 48/72, and 96 hrs) and the fungus was allowed to grow on fumonisin production media (e.g. GYAM). The overall goal for these three libraries was to identify differentially expressed genes important to fumonisin biosynthesis. Growth conditions of remaining four libraries included a plant (maize) component. The overall goal for this set of libraries was to identify differentially expressed genes important for fungal/plant interactions. The first library of this set was prepared from F. verticillioides spores germinated for 10 hrs in water extracts of maize seedlings; the second library was prepared from the fungus grown on excised maize seedling roots and shoots; the third library was prepared from the fungus grown on developing maize kernels; and the fourth library was a subtracted library prepared from fungal culture with or without 2-benzoxazolinone (BOA), an antimicrobial compound produced by maize. A total of 55,150 ESTs have been generated which represent 10,539 unique ESTs. 50,432 ESTs align to generate 5,816 tentative consensus (TC) sequences leaving 4,716 sequences as singletons. Comparison of each collection, or library against the total collection is beginning to identify subsets of genes that may play a specific role in fumonisin biosynthesis as well as fungal plant interactions. For example, there are 756 unique ESTs within the 48/72 hr GYAM library and 888 unique ESTs within the 96 hr FPM library. Almost all of the fumonisin cluster (FUM) genes are represented in the 48/72 hr GYAM library (13/15) while all FUM genes are represented in the 96 hr GYAM library. No FUM genes are represented in the 24 hr GYAM library. We are in the process of developing DNA microarray containing a complete set of all the unique genes to identify differentially expressed genes from different growth conditions. Both experimental systems will help identify important regulatory genes whose characterization may lead to the development of new fungal or fumonisin control strategies in the field.