Location: Sustainable Perennial Crops LaboratoryTitle: A potential role for an extracellular methanol oxidase secreted by Moniliophthora perniciosa in Witches' broom disease in cacao) Author
|Rio, Maria Carolina|
Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2012
Publication Date: 11/12/2012
Citation: Oliveira, B., Teixeira, G., Reis, O., Barau, J., Teixeira, P.J., Rio, M.S., Domingues, R.R., Meinhardt, L.W., Leme, A.F., Rincones, J., Pereira, G.A. 2012. A potential role for an extracellular methanol oxidase secreted by Moniliophthora perniciosa in Witches' broom disease in cacao. Fungal Genetics and Biology. 49:922-932. Interpretive Summary: The basidiomycete fungus Moniliophthora perniciosa causes witches’ broom disease (WBD) of cacao (Theobroma cacao), and is one of the most devastating diseases of cacao in the Americas. This disease has greatly reduced the yield of cacao, the source of chocolate, from this growing region. Recent genomic studies of this fungus have found sequences similar to methanol oxidase (MOX). MOX is the main enzyme involved in the breakdown of methanol. In this study, we demonstrate that M. perniciosa produces methanol as it breaks down the pectin in between the plant cell walls and uses the enzyme methanol oxidase to consume the methanol. This helps the fungus grow without being affected by the methanol it produces. We also show that M. perniciosa has all of the genes required to use methanol and the expression of these genes indicates that methanol can be a energy source for the growth of this fungus. This information broadens our knowledge of the plant disease interactions and will help researchers and plant breeders find and/or develop improved disease resistant crops.
Technical Abstract: The hemibiotrophic basidiomycete fungus Moniliophthora perniciosa, the causal agent of witches’ broom disease (WBD) of cacao, is able to grow in methanol as sole carbon source. In plants, one of the main sources of methanol is the pectin present in the structure of cell walls. Pectin is composed by highly methylesterified chains of galacturonic acid. The hydrolysis of galacturonic acid in esterified pectin by the methyl radicals is mediated by a pectin methylesterase (PME) and releases methanol, which may be decomposed by a methanol oxidase (MOX). The analysis of M. pernciosa genome revealed putative MOX and PME sequences. Real-time RT-PCR conducted with RNA from the mycelia grown in the presence of methanol or pectin and with RNA of infected cacao plants in different stages of the progression of WBD indicate that both genes are co-regulated, suggesting that the fungus may be metabolizing the methanol released from pectin. Immunolocalization of pectin epitopes in cacao plants infected with M. perniciosa shows a reduction in the degree of pectin esterification. Although MOX is a classical peroxisomal enzyme, M. perniciosa presents an extracellular methanol oxidase. Its activity was detected in the fungus culture supernatants and mass spectrometry analysis indicated the presence of this enzyme in the fungus secretome. As M. pernciosa possesses all genes classically related to the methanol metabolism, we propose a model for the utilization of methanol by this fungus, which begins with the extracellular oxidation of methanol derived from the demethylation of pectin and finishes in the cytosol.