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| Author(s): |
Daniela Paula de Toledo Thomazella
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia |
| Defense date: | 2010-09-12 |
| Examining board members: |
Gonçalo Amarante Guimarães Pereira;
Gisele Monteiro;
Luis Eduardo Soares Netto;
Marcelo Menossi;
Paulo Arruda
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| Advisor: | Johana Rincones; Gonçalo Amarante Guimarães Pereira |
| Abstract | |
Moniliophthora perniciosa and Moniliophthora roreri are phytopathogenic basidiomycetes, which cause two of the most devastating fungal diseases of cacao: the Witches' Broom and Frosty Pod Rot diseases, respectively. Despite the great socioeconomic impact of the diseases, important aspects of the metabolism of these pathogens are not sufficiently understood. The mitochondrial metabolism is particularly important since it is associated with many cellular processes of crucial importance for the organism survival, such as the regulation of energy production (ATP) and the maintenance of the cellular redox balance. This study aimed to understand the importance of the mitochondrial enzyme alternative oxidase (AOX) in the metabolism and development of the cacao pathogens M perniciosa and M. roreri. AOX is a non-phosporylating ubiquinol oxidase which catalyzes the reduction of molecular oxygen to water. In M. perniciosa, the expression of aox gene {Mp-aox) was closely related to the hemibiotrophic lifestyle of this fungus. High levels of Mp-aox transcripts were observed in the biotrophic mycelium and, accordingly, it showed an elevated sensitivity to AOX inhibitors, suggesting that AOX has a role in the development of the biotrophic phase. Interestingly, the in vitro inhibition of the cytochrome-dependent pathway prevented the transition from biotrophy to necrotrophy. Furthermore, the combined use of an inhibitor of the cytochrome pathway with an AOX inhibitor completely impaired the in vitro fungal growth as well as prevented the establishment of the disease in cacao seedlings. Based on these data, this study suggests a model in which the involvement of the different pathways of electron transfer (cytochrome and alternative routes) regulates the development of the biotrophic mycelium and the phase transition of M. perniciosa in planta. This is the first report presenting strong evidences for a role of AOX during the in pfanta development and life cycle of a phytopathogenic fijngus. Like M. perniciosa, the aox gene of M. roreri {Mr-aox) is up-regulated after exposure of the fungal mycelium to the fungicide azoxystrobin (a potent inhibitor of complex III}, suggesting that AOX plays a protective role against the deleterious oxidative stress produced by the compound. However, even with the increased expression of Mr-aox, M. roreri growth was highly sensitive to the fungicide. Therefore, it is possible that AOX activation was not enough to overcome the toxic effects of the cytochrome pathway inhibition and, consequently, M. roreri presented a high susceptibility to oxidative stress. Finally, the combined application of azoxystrobin and an AOX inhibitor completely impaired the in vitro development of M. roreri Thus., based on these results, we suggest that AOX has a role in the metabolism of these cacao pathogens and the concomitant inhibition of both cytochrome and alternative pathways may be an efficient strategy for the control of Witches' Broom and Frosty Pod Rot diseases. (AU) | |