Identificação e análise funcional de efetores de Hemileia vastatrix, agente causal da ferrugem do cafeeiro

• Autor(a) principal: Maia, Thiago Andrade
• Data de Publicação: 2013
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1069
• topic: Ferrugem-do-cafeeiro; Hemileia vastatrix; Interação planta-patógeno; Café - Resistência a doenças e pragas; Rust in coffee; Hemileia vastatrix; Plant-pathogen; Coffee - Resistance to diseases and pests; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::FITOPATOLOGIA

Coffee leaf rust, caused by the biotrophic fungus Hemileia vastatrix, is the main phytosanitary problem of the coffee plant. The disease may cause yield losses ranging from 35 to 50% if control measures are not implemented. During the interaction with the host plant, rust fungi secrete a variety of effector proteins that modify the structure and function of the host cell allowing the biotrophic interaction. Some of these effector proteins, known as avirulence proteins (Avr), are recognized by plant proteins encoded by resistance genes, which triggers a defense response against pathogen infection. At least nine dominant genes (SH1 to SH9) that confer resistance to coffee leaf rust have been genetically identified, but despite many years of research on this pathosystem, the complementary Avr genes of H. vastatrix have not yet been identified or characterized. One approach that can be used for this purpose is to conduct an transcriptome and bioinformatics analyses in order to identify candidate genes of H. vastatrix that fulfill a set of specific criteria common to effector proteins, and their validation by conducting functional assays for effector activities. Therefore, the objectives of this study were: (i) to identify genes of H. vastatrix that encode proteins secreted during the germination of urediniospores as well as during the biotrophic interaction with the coffee plant, (ii) to express the effector gene candidates from H. vastatrix in the yeast secretion trap system (YST) in order to obtain biological confirmation of the secretion prediction made by bioinformatics tools, (iii) to analyze the genomic structure of a select group of effector gene candidates, (iv) to perform expression analysis of the identified candidates during different stages of infection; and (v) to establish a protocol for transient expression of H. vastatrix secreted proteins in coffee leaves based on the Type III Secretion System of Pseudomonas syringae pv. garcae. Initially, the secretome of germinated urediniospores of H. vastatrix was characterized by constructing a cDNA library from mRNA isolated from urediniospores germinated in vitro during 16 hours. After analysis of the ESTs using bioinformatics tools, 146 ORFs that encode secreted proteins were selected. Annotation of these proteins showed that 20% of the secretome from germinated urediniospores consists of hydrolytic enzymes and that most (67%) of the identified secreted proteins have unknown function. From the latter group of sequences, 35 complete ORFs encoding proteins sharing features with effectors from filamentous fungi and named H. vastatrix effector candidates (HvECs) were selected for further analysed. The genomic sequences of 22 of these HvECs were characterized, confirming the ORFs predicted by bioinformatics. The secretion of eight selected HvECs was confirmed in yeast and their expression analysis revealed a differential expression, which possibly occurs in coordination with the morphological changes of the pathogen during the early stages of infection. The secretome of H. vastatrix during a compatible plant-rust interaction was also characterized by a combination of Sanger sequencing and 454 pyrosequencing. This integrated approach allowed the massive sequencing of a substantial number of sequence tags (ESTs) of genes expressed at four different times during the biotrophic interaction: 48 hours, 72 hours, 9 days and 12 days after inoculation of coffee leaves with H. vastatrix. After bioinformatics analyses of these ESTs, 75 HvECs were selected and an expression analyses based on RT- PCR confirmed the fungal origin for 62 of them. 22 of these HvECs are preferentially expressed during the interaction of the fungus with the coffee plant and show distinct patterns of expression along the progress of infection. Using the pEDV system and the Type III Secretion System of P. syringae pv. garcae it was established a protocol to express transiently secreted proteins from H. vastatrix in coffee leaves established. Transient expression of HvEC-016 inside the cytoplasm of coffee plants carrying the rust resistant gene SH1, triggered a plant defense response indicating that there may have occurred a recognition of the HvEC-016 effector protein mediated by the R protein encoded by SH1. The catalog of effector gene candidates for H. vastatrix expressed during both urediniospore germination and the interaction with the coffee plant and the transient assay established in this study is an important plataform to identify additional avirulence genes from Hemileia vastatrix.