Early development of Moniliophthora perniciosa basidiomata and developmentally regulated genes
Authors: Pires Acássia BL , Gramacho Karina P , Silva Delmira C , Góes-Neto Aristóteles , Silva Mylene M , Muniz-Sobrinho Jairo S , Porto Ricardo F , Villela-Dias Cristiano , Brendel Martin , Cascardo Júlio CM , Pereira Gonçalo AG 
Published: August 2009

Background

The hemibiotrophic fungusMoniliophthora perniciosais the causal agent of Witches' broom, a disease ofTheobroma cacao. The pathogen life cycle ends with the production of basidiocarps in dead tissues of the infected host. This structure generates millions of basidiospores that reinfect young tissues of the same or other plants. A deeper understanding of the mechanisms underlying the sexual phase of this fungus may help develop chemical, biological or genetic strategies to control the disease.

Results

Mycelium was morphologically analyzed prior to emergence of basidiomata by stereomicroscopy, light microscopy and scanning electron microscopy. The morphological changes in the mycelium before fructification show a pattern similar to other members of the orderAgaricales. Changes and appearance of hyphae forming a surface layer by fusion were correlated with primordia emergence. The stages of hyphal nodules, aggregation, initial primordium and differentiated primordium were detected. The morphological analysis also allowed conclusions on morphogenetic aspects. To analyze the genes involved in basidiomata development, the expression of some selected EST genes from a non-normalized cDNA library, representative of the fruiting stageof M. perniciosa, was evaluated. A macroarray analysis was performed with 192 selected clones and hybridized with two distinct RNA pools extracted from mycelium in different phases of basidiomata formation. This analysis showed two groups of up and down-regulated genes in primordial phases of mycelia. Hydrophobin coding, glucose transporter, Rho-GEF, Rheb, extensin precursor and cytochrome p450 monooxygenase genes were grouped among the up-regulated. In the down-regulated group relevant genes clustered coding calmodulin, lanosterol 14 alpha demethylase and PIM1. In addition, 12 genes with more detailed expression profiles were analyzed by RT-qPCR. One aegerolysin gene had a peak of expression in mycelium with primordia and a second in basidiomata, confirming their distinctiveness. The number of transcripts of the gene for plerototolysin B increased in reddish-pink mycelium and indicated an activation of the initial basidiomata production even at this culturing stage. Expression of the glucose transporter gene increased in mycelium after the stress, coinciding with a decrease of adenylate cyclase gene transcription. This indicated that nutrient uptake can be an important signal to trigger fruiting in this fungus.

Conclusion

The identification of genes with increased expression in this phase of the life cycle ofM. perniciosaopens up new possibilities of controlling fungus spread as well as of genetic studies of biological processes that lead to basidiomycete fruiting. This is the first comparative morphologic study of the early development bothin vivoandin vitroofM. perniciosabasidiomata and the first description of genes expressed at this stage of the fungal life cycle.