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| Author(s): |
Valesca Pandolfi
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB) |
| Defense date: | 2006-09-11 |
| Examining board members: |
Helaine Carrer;
Luis Eduardo Aranha Camargo;
Alan Mitchell Durham;
Augusto Etchegaray Júnior;
Antonio Vargas de Oliveira Figueira
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| Advisor: | Helaine Carrer |
| Abstract | |
Cultivated grasses such as wheat, barley and maize are agricultural products of fundamental economic and social importance in Brazil. Among causing factors of important grain production losses in these species are diseases caused by phytopathogenic fungi such as Fusarium graminearum Schwabe (teleomorfo Gibberella zeae Schw.), the causal agent of fusariosis, a disease of difficult chemical, biological or even genetic control. An efficient and promising strategy to be adopted in order to protect cultivated plants against such diseases is the selection of antagonist microorganisms, amongst them the bacteria Pantoea agglomerans. This microbiota might have an important impact in scab control, isolated or in an integrated management program with chemical treatment. The present work aimed at identifying differentially expressed sequences in pathogenic fungi-antagonistic microorganisms interactions, considering the F. graminearum ? P. agglomerans model. The construction of a cDNA library for F. graminearum grown in PDA medium generated 1,983 valid sequences and provided 1,283 unigenes. The most representative categories in this library were proteins involved in genetic information pathways, DNA-RNA-protein (26 %); hypothetical proteins (24 %); and proteins involved in metabolism (16 %). The protein category involved in developmental processes as well as those related to external stimuli perception comprised 10 % of the obtained unigenes. Among putatively annotated genes, some coding for enzymes of important metabolic routes were identified, such as glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase and phophoenolpyruvate carboxylase. Also secondary metabolism compounds, specially micotoxins and proteins related to fungi stresses and pathogenicity were identified. In the present work, the control of three wheat phytopathogens, Drechslera tritici-repentis (Died.) Shoem, Bipolaris sorokiniana (Sacc.in Sorok.) and F. graminearum, using specific isolates of P. agglomerans was demonstrated. It was observed that the 50 % and 40 % growth inhibition of these fungi is associated to the bacteria release of soluble and volatile compounds, respectively. The gene expression profile of F. graminearum during interaction with the bacteria P. agglomerans was evaluated via macroarray. Among the 1,014 analysed genes, 29 F. graminearum genes were differentially expressed (p < 0,05) during its interaction with the antagonist bacteria: 19 genes were induced while 10 genes were repressed. Among the induced transcripts, proteins involved in fungi defense and/or virulence processes were identified, whose expression was induced in reponse to abiotic or biotic stresses. Among the identified repressed genes, a transcript similar to a protein containing a zinc finger-type domain, a transcription factor relevant in cell division, deserves special attention, as well as proteins involved in respiratory chain, in protein modulation and in cell signaling. Additionally, the macroarray data were validated by reverse transcription followed by real-time quantitative PCR (RT-PCRq), a suitable method for complementing transcriptional analysis through macroarray. Finally, the information generated in in vitro pathogenic fungi-antagonistic microorganisms interactions analysis, as well as in the analysis and sequencing of the obtained transcripts, together with the determination of the level of expression during the evaluated interactions were essential for better understanding the response pattern of the fungus F. graminearum in interaction with the bacteria P. agglomerans (AU) | |