Browsing by Subject "transcription factors"
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Item Molecular Characterization of MADS-BOX Transcription Factors and Analysis of Field Population Diversity in the Maize Pathogen Fusarium verticillioides(2013-04-10) Ortiz, Carlos SFusarium 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.Item The Role of Cys2-His2 Zinc Finger Transcription Factors in Polyol Metabolism, Asexual Development and Fumonisin Biosynthesis in Fusarium verticillioides(2013-04-12) Malapi-Wight, Martha MariaThe ascomycete Fusarium verticillioides (Sacc.) Nirenberg (teleomorph: Gibberella moniliformis Wineland) causes stalk and ear rots on maize worldwide. In addition to the economic losses due to reduced yield, the fungus produces fumonisins on infected corn. One of the unanswered questions in mycotoxin research is how fungi perceive and respond to various extracellular stimuli and produce mycotoxins. To date, extensive research has been performed on important signaling pathways that regulate mycotoxin biosynthesis, but little is known about the downstream target genes, notably transcription factors (TFs). While the roles of TFs have shown to be critical in eukaryotic transcription regulation, only a few have been characterized in F. verticillioides. TFs with zinc fingers have been reported in all living organisms, and in fungal species, members of the Cys2-Hys2 (C2H2) zinc finger TF family are predicted to be involved in cell differentiation, carbon utilization, and development. Using the available genomic resources, I constructed a library of C2H2 TF deletion mutants, and identified SDA1, FvFLBC and CHT1 genes with a potential role in carbon utilization, development and fumonisin B1 (FB1) biosynthesis. The ?sda1 strain showed complete growth inhibition when using sorbitol as the sole carbon source and produced higher levels of FB1 when grown on corn kernels. In addition, the ?sda1 strain produced less number of conidia compared to the wild-type progenitor. Through gene complementation, I also demonstrated that F. verticillioides SDA1 and Trichoderma reesei ACE1 are functionally conserved. FvFLBC acts as a regulator of asexual development but not FB1 biosynthesis. I also discovered that the FvFlbC N-terminus is critical for conidia production. CHT1 is associated with asexual development, fumonisin biosynthesis and pigmentation. Characterization of key signal transduction pathways, and more importantly the function of SDA1, FvFLBC and CHT1, should facilitate the elucidation of the mechanisms and regulations of growth, development, and secondary metabolism in F. verticillioides. The outcome of this study may help us determine how to minimize F. verticillioides contamination of crops and the resulting mycotoxins, providing safer and higher value corn in the US and worldwide.