Univ., Diss., 2009--Marburg.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1952. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 24-27).

Univ., Diss., 2009--Marburg.

Erlangen-Nürnberg, Univ., Diss., 2010.

Universiẗat, Diss., 2001--München.

Universiẗat, Diss., 2001--München.

Universiẗat, Diss., 2001--München.

Nutritional mutants of Ustilago hordel were used to demonstrate that parasexual recombination occurs within the host plant (Hordeum vulgare) prior to the production of teliospores. The nutritional mutants were also used to show that resistance of the newly-germinated seedling of H. vulgare to U. hordei and of subsequently formed tillers to infection was not correlated, and was probably not controlled by the same gene or genes. The application of gibberellic acid to H. vulgare was found to cause an increase in the overall tiller height of healthy plants by increasing the elongation of Internodal regions 0-1, 1-2, 2-3, and 3-4. There was no increased elongation of internodal regions 4-5 and 5-6. The healthy tillers of diseased plants showed no Internodal elongation when gibberellic acid was applied. Diseased tillers, which are usually shorter than healthy tillers, were also unaffected by the presence of gibberellic acid. The injection of both mating types of U. hordei into the young developing spike of a normally resistant strain of H. vulgare resulted in the production of diseased spikes. This would indicate that blockage to normal infection occurs at the time of seedling penetration, at the level of tiller primordia development, or at the time of spike primordia development. / Science, Faculty of / Botany, Department of / Graduate

Graduation date: 1991

The basidiomycete cereal pathogens Ustilago hordei and U. maydis are closely related and possess genomes with a high degree of homology and synteny. I report on the disparity of the RNAi phenomenon between U. hordei and U. maydis. Using an RNAi expression vector I targeted both a GUS transgene and an endogenous mating-type gene and confirmed the presence of double-stranded (ds)RNA in transgenic cells of both species. However, down-regulation of the GUS gene and production of siRNAs were seen only in U. hordei. The biological effect was a reduction in GUS protein and activity, and reduced mating only in U. hordei. In support of this experimental evidence, homologs to Dicer and Argonaute were found in the U. hordei genome but not in the published U. maydis genome. Interestingly, preliminary U. hordei sequences reveal conservation and synteny in U. maydis in the regions spanning these loci, with the only noticeable difference being the lack of Dicer and Argonaute genes in U. maydis. U. maydis also appears to differ from U. hordei with respect to genes presumed to be involved in transcriptional gene silencing and also has far fewer transposons in its genome. Efforts to clone the avirulent gene UhAvr1 led to a locus containing a large number of small proteins predicted to be secreted. This locus appears to be heterochromatic and is orthologous to the largest cluster of secreted proteins in U. maydis. Other laboratories have reported that deletion of this cluster in U. maydis results in a dramatic reduction in virulence. Genetic evidence for an avirulence gene at this locus in U. hordei suggests that the locus may also be important for U. hordei. Differences between these two smut fungi at this locus and at others identified in this study point to key differences in gene regulation and genome evolution.