<p>  </p> <p>Adenosine-to-Inosine (A-to-I) mRNA editing is a post-transcriptional modification of specific sites within the mRNA that has only recently been observed in filamentous fungi. In the wheat scab fungus <em>Fusarium graminearum,</em> this phenomenon has shown to be facilitated by FgTad2 and FgTad3, homologs of Adenine Deaminase Acting on tRNA (ADAT). Interestingly, these two proteins are constitutively expressed in all different life stages<em>, </em>in contrast to only the sexual stage-specific nature of A-to-I mRNA editing in <em>F. graminearum</em>. To understand the molecular mechanisms regulating this process, six candidate co-factor genes were identified which interact with FgTad2 and/or FgTad3, specifically during sexual reproduction. Deletion mutants of four candidate co-factor genes were successfully generated. All four mutants displayed normal asexual development of <em>F. graminearum</em>, but four mutants also altered sexual function. Those four mutant led to formation of morphologically normal perithecia and ascospores, but the perithecia failed to discharge ascospores. More interestingly, in <em>FGSG_10943 </em>deletion mutant, most of these ascospores germinated precociously within the perithecium. I also observed, that among the candidate co-factor genes which are specifically expressed during sexual reproduction, <em>FGSG_10943</em> was significantly upregulated during the later stage of sexual development. This gene is restricted in nature to only a few orders of fungi in the class Sordariomycetes that form dark pigmented ascocarps, particularly Hypocreales and Glomerellales. Taken together, these results indicate that the four candidate co-factor genes are dispensable for vegetative growth of the fungus and involved in ascospore discharge. <em>FGSG_10943</em> appears to be involved in autoinhibition of ascospores inside the perithecia and interact with FgTad2 during sexual reproduction to mediate A-to-I mRNA editing in <em>F. graminearum</em>.</p>

Fusarium graminearum (Schwabe), causal organism of fusarium head blight (FHB), has become a major pathogen of wheat (Triticum aestivum L.) throughout North America. Since its discovery in the United States, the disease has spread south and east until at present it is an annual threat for growers of winter wheat in the Mid-Atlantic region. Yield losses for soft red winter (SRW) wheat averaged 908 kg ha-1 in the FHB outbreak of 1998 (Griffey et al., 1999). The economic loss from this single FHB epidemic was an estimated 8.5 million dollars. Environmental conditions favorable for FHB development, including above average rainfall and temperatures during anthesis, have become more common in the Upper-Midwestern wheat-growing region over the past decade, leading to substantial losses in wheat and barley crops. This, coupled with low prices being paid for wheat, has prompted research toward solving the problem of FHB across the nation. The majority of labor and financial resources devoted to FHB research are dedicated to incorporating FHB resistance into adapted wheat lines. While this is a prudent method of combating this disease, this process will take many years to complete. We have examined all FHB assessment parameters, which include FHB incidence, FHB severity, FHB index, percentage fusarium damaged kernels (percentage FDK), and 15-acetyl deoxynivalenol toxin (DON toxin) accumulation, to ascertain which assessment parameters best quantify FHB resistance levels in addition to grain yield and grain volume weight (GVW) losses. FHB index provides the most reliable in-field assessment of a genotype's resistance level, whereas percentage FDK provides a reliable measure of a genotype's resistance level post-harvest. FHB index and percentage FDK are also the most predictive assessment parameters with regard to grain yield and GVW loss. A wide range in both level and type of resistance was observed among genotypes examined in this study. The cultivars Agripro Patton, Ernie, INW9824, Roane, and the experimental line NY87048W-7388 consistently had lower scores for FHB assessment parameters and lower losses of grain yield and GVW. / Master of Science

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Fusarium head blight is a devastating fungal disease of cereals caused by the pathogen Fusarium graminearum that leads to important economic losses due to diminished yields and grain downgrading. F. graminearum deploys several secondary metabolites known as virulence factors to facilitate its invasion of host tissues. These include the gramillins, a group of bicyclic lipopeptide ionophores that cause cell death and increased virulence in Arabidopsis, maize, and barley, but not wheat. Ionophores are involved in many plant-microbe interactions, but current knowledge of the molecular mechanisms governing host response to these molecules is limited. Susceptibility to gramillin varies among cultivars of affected species, but the basis for insensitivity has not yet been described, nor has the function of gramillin during infection. Here, we establish ion leakage as a method to survey Canadian barley for sensitivity, demonstrate that insensitivity to gramillin is likely mediated by a plant protease rather than inducible immune responses, and suggest a possible function of gramillin in positively regulating the expression of other fungal virulence factors during infection. This contributes to deepening our understanding of cyclic lipopeptide ionophores and their role during plant-microbe interactions.

Fusarium head blight (FHB) is a horribly destructive fungal diseases of barley. FHB is caused by a species complex of Fusaria, of which Fusarium graminearum Schwabe is the main causal species of FHB epidemics in Canada. Field surveys show that two or more Fusarium species often co-exist within the same field or grain sample and F. poae is reported as another important species in barley in Ontario and Quebec. The aim of this study was to observe the pathogenicity of F. graminearum, F. poae and a co-inoculation of both species causing FHB in barley. Two susceptible barley cultivars were spray-inoculated at 10 to 14 days after heading. Phenotypic disease severity was rated on a scale of 0-9 at 4, 7, 14, 21, and 28 days after inoculation. There was a significant difference in FHB severity between F. graminearum and F. poae, where infection with F. graminearum produced more severe disease ratings. F. poae generated lower disease ratings and was not statistically different from the control. When heads were co-inoculated with both Fusarium species, the resulting FHB severity was unchanged 54relative to heads inoculated with F. graminearum only. The ratio of F. graminearum to F. poae genomic DNA was also no different than when heads were inoculated with F. graminearum alone, as quantified with ddPCR using markers specific to each species. Metabolomic analysis of sample extracts corroborated our other findings where F. graminearum appeared to outcompete F. poae in barley also at the mycotoxin level. Barley cultivar did not have a significant effect on visual FHB disease ratings and fungal DNA detection, however there were some chemical differences between cultivars in response to challenge by both F. graminearum and F. poae.

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