Exserohilum turcicum is the hemibiotrophic causal agent of Northern leaf blight of maize and sorghum. Despite the global importance of this yield-limiting pathogen, knowledge regarding genes contributing to disease development and race-specificity is limited. Therefore, this study aimed to identify genes involved in host colonization during biotrophic and necrotrophic phases of infection, as well as race-specific differences in gene expression. RNAseq of maize seedlings inoculated with a race 13N or 23N E. turcicum isolate was conducted to identify genes contributing to fungal pathogenicity, and expression was validated for four effector candidates. A population genetic study was undertaken of isolates from maize and sorghum to select isolates for sequencing of three putative effectors. Fungal biomass positively correlated with the percentages of E. turcicum reads mapped and indicated a lifestyle switch from biotrophy to necrotrophy between 7 and 13 dpi. Transcriptome sequencing enabled identification of cell wall degrading enzymes, peptidase-encoding genes, secondary metabolite biosynthesis genes and candidate effectors likely contributing to the pathogenicity of E. turcicum. Profiling of Ecp6 and candidate effector SIX13-like revealed increased expression at 5 and 7 dpi compared to 2 and 13 dpi. Evidence of host specificity was obtained from microsatellite haplotypes and sequencing of SIX13-like. Identification of candidate effector SIX13-like is consistent with the colonization of E. turcicum through the xylem of susceptible hosts and possibly indicates specificity of E. turcicum to either maize or sorghum. This study identified E. turcicum genes putatively involved in pathogenicity and describes a hypothetical model of the E. turcicum – maize interaction. / Thesis (PhD)--University of Pretoria, 2019. / The financial assistance of the National Research Foundation (NRF South Africa, grant unique numbers 85847, 88785, 92762 and 93671) toward this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the authors and are not necessarily to be attributed to the NRF. / Plant Science / PhD / Unrestricted

Sugarcane smut is a worldwide distributed disease important to agribusiness, since it can affect sugarcane yield drastically. The disease is caused by the Basidiomycete Sporisorium scitamineum, a biotrophic fungus that colonizes mainly sugarcane. Sugarcane-smut interaction has been extensively studied by this research group for the past few years in their various aspects, considering both the pathogen attack and plant defenses. This work aimed to functionally address fungal candidate effector proteins associated with this pathosystem. Effectors are essential to modulate host metabolism to allow pathogen colonization. The identification of such proteins may assist in recognition of resistance genes relevant to genetic breeding programs. Based on the complete genome sequence of S. scitamineum and the dual transcriptomic data candidate genes were selected in silico. Selection strategies were based on the predicted secretome and differential expression levels of the genes in planta. Candidate effectors were analyzed regarding their expression pattern, subcellular location and influence over basal plant defenses and plant immunity. The results showed that the S. scitamineum candidate effector genes are expressed under the influence of the host genotype. It was observed various expression patterns in the set of selected genes and differential subcellular localization patterns. These results will enable future researches considering virulence level of different isolates and also help decision making in plant breeding programs. / O carvão da cana-de-açúcar é uma doença cosmopolita de grande importância para o agronegócio, uma vez que pode afetar a produtividade da cultura. A doença é causada pelo basidiomiceto Sporisorium scitamineum, fungo biotrófico que coloniza exclusivamente a cana-de-açúcar. A interação cana-carvão vem sendo extensivamente estudada por este grupo de pesquisa nos últimos anos em seus vários aspectos, considerando as atividades de ataque e defesa do patógeno e da planta, respectivamente. Este trabalho teve como finalidade o estudo funcional de proteínas candidatas a efetores neste patossistema. Efetores são moléculas essenciais na manipulação do metabolismo e fisiologia do hospedeiro de forma a permitir sua colonização. A identificação de tais proteínas auxilia no reconhecimento de genes de resistência podendo gerar informações relevantes a programas de melhoramento genético na produção de variedades resistentes. A estratégia de seleção utilizada se baseia em características do secretoma predito e da expressão diferencial de genes do patógeno in planta. Os candidatos foram analisados quanto ao padrão de expressão gênica, à localização sub celular e sua influência sobre a defesa basal e imunidade em plantas. Os resultados demonstraram que a expressão dos genes que codificam para as proteínas efetoras de S. scitamineum e é influenciada pelo genótipo das plantas infectadas. Foram observadas variações no padrão de expressão entre o conjunto de efetores selecionados, bem como padrões diferenciais de localização sub celular e influência sobre a imunidade em plantas. Os resultados gerados por este trabalho servirão de subsídio para estudos futuros sobre os níveis de virulência dos diferentes isolados do patógeno bem como para auxiliar a tomada de decisão em programas de melhoramento genético de variedades resistentes ao carvão da cana.