Molecular Characterization of MADS-BOX Transcription Factors and Analysis of Field Population Diversity in the Maize Pathogen Fusarium verticillioides
Fusarium verticillioides (Teleomorph Giberella moniliformis) is an ascomycete fungus responsible for ear and stalk rots of maize. Most importantly, it produces a group of mycotoxins called fumonisins upon colonization of maize kernels. Fumonisin B1 (FB1), the most prevalent fumonisin in nature, was first identified in 1988 and has been found to be toxic to human and animals. The gene cluster for FB1 biosynthesis and some environmental conditions responsible for the toxin production are known, but gaps in our understanding of the signaling pathways leading to FB1 biosynthesis still remain. MADS-box transcription factors (TF) are known to regulate diverse cellular functions in all eukaryotes, and in silico analyses revealed two genes, MADS1 and MAD2, in F. verticillioides. Reverse genetics studies indicated that MADS1 and MADS2 positively regulate sexual mating and FB1 biosynthesis but not pathogenicity in F. verticillioides. Furthermore, MADS1 was found to act as a broad regulator of polyketide-derived secondary metabolism. Additionally, population diversity studies were conducted in 164 F. verticillioides cultures isolated from 65 maize-producing counties in Texas. The result showed a fluid population with no particular niches formed. F. verticillioides strains were also isolated from counties that have previously tested negative for FB1 contamination in maize. The presence of the pathogen represents a risk for future FB1 contamination events if suitable conditions were to arise. My research revealed new genetic components involved in F. verticillioides secondary metabolite biosynthesis and provided a better understanding of the pathogen population fluidity in Texas.