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Abstract
Fusarium species are diverse and economically important soilborne phytopathogenicfungi. Though Fusarium verticillioides potentially infects various plants, it plays a diverse role in the ecosystem as both a significant pathogen of corn, causing root, kernel, seed, and stalk rots, and as a symptomless intercellular endophyte of maize. We hypothesize that the economically important maize pathogen and symptomless endophyte, F.verticillioides, is a good candidate for horizontal gene transfer (HGT) detection given its versatile lifestyles. Horizontal gene transfer, the exchange and stable integration of genetic material between different evolutionary lineages, is believed to shape genomes and populations and produce a gain of adaptive advantages. To identify such phenomenon in F.verticillioides, a genome-wide identification of HGT events using a phylogenomic pipeline was conducted followed by manual curation, obtaining 117 strong HGT candidates of which most were putatively acquired from bacteria. Functional categorization of these candidates implicated several enriched biochemical activities compared to the frequency of such genes within the genome. Multiple interesting HGT candidates that are narrowly distributed within fungi or induced only under specific environmental conditions were identified. A prime exemplar was FVEG_10494, a strong HGT candidate with orthologs in only a few Fusarium species, and it was highly and specifically up-regulated under nitric oxide (NO) challenge. Secondly, functional characterization was performed on two catalase/peroxidase genes named FvCP01 and FvCP02, which were previously identified as HGT candidates broadly distributed among ascomycetes. In vitro hydrogen peroxide (H2O2) sensitivity and quantitative reverse transcription-PCR (qRT-PCR) analyses suggest differential responses of these two genes to in vitro versus in planta oxidative challenges. FvCP01 seems to be largely involved in non-host-mediated H2O2 stress while FvCP02 is mainly responsible for oxidative challenge derived from the host. Lastly, a project was initiated to develop a chemical-inducible expression system in F.verticillioides based on a system used in plants.