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Molecular systematics of the dimorphic ascomycete genus Taphrina
Manuel G Rodrigues1, Álvaro Fonseca1
1Centro de Recursos Microbiológicos (CREM), Secção Autónoma de Biotecnologia, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Portugal.
Abstract:
The ascomycete genus Taphrina Fries comprises nearly 100 species recognized by their mycelial states when parasitic on different vascular plants. Whereas the filamentous state is strictly phytoparasitic, the yeast state is saprobic and can be cultured on artificial media. Taphrina species are differentiated mainly on the basis of host range and geographical distribution, type and site of infection and morphology of the sexual stage in infected tissue. However, there has been little progress in the systematics of the genus in recent years, mainly because of the scarcity of molecular studies and available cultures. The main aim of the present study was the reappraisal of species boundaries in Taphrina based on the genetic characterization of cultures (yeast states) that represent about one-third of the currently recognized species. The molecular methods used were (i) PCR fingerprinting using single primers for microsatellite regions and (ii) determination of nucleotide sequences of two approx. 600 bp nuclear rDNA regions, the 5' end of the 26S rRNA gene (D1/D2 domains) and the internal transcribed spacer region (which includes the 5.8S rRNA gene). Sequencing results confirmed the monophyly of the genus (with the probable exclusion of Taphrina vestergrenii) and the combined analysis of the two methods corroborated, in most cases, separation of species defined on the basis of conventional criteria. However, genetic heterogeneity was found within some species and conspecificity was suggested for strains that have been deemed to represent distinct species. Sequences from the ITS region displayed a higher degree of divergence than those of the D1/D2 region between closely related species, but were relatively conserved within species (> 99% identity) and were thus more useful for the effective differentiation of Taphrina species. The results further allowed other topics to be addressed such as the correlation between the molecular phylogenetic clustering of certain species and the respective host plant family and the significance of molecular methods in the accurate diagnosis of the different diseases caused by Taphrina species.
Insights
This study genetically characterized Taphrina yeast states, confirming species boundaries using molecular methods. It found the internal transcribed spacer (ITS) region effective for differentiating Taphrina species.
Area of Science:
- Mycology
- Plant Pathology
- Molecular Systematics
Background:
- The ascomycete genus Taphrina includes nearly 100 species, primarily identified by their parasitic filamentous and saprobic yeast states.
- Traditional species differentiation relies on host range, infection type, and morphology, with limited recent progress due to scarce molecular data and cultures.
Purpose of the Study:
- To reappraise species boundaries within the Taphrina genus using genetic characterization of cultured yeast states.
- To assess the utility of molecular methods for Taphrina systematics and species differentiation.
Main Methods:
- PCR fingerprinting with microsatellite primers.
- Nucleotide sequencing of nuclear ribosomal DNA (rDNA) regions: 26S rRNA gene (D1/D2 domains) and the internal transcribed spacer (ITS) region.
Main Results:
- Molecular analyses confirmed the monophyly of Taphrina (excluding T. vestergrenii).
- Combined methods corroborated most conventionally defined species boundaries, but revealed genetic heterogeneity within some species.
- The ITS region showed higher divergence between closely related species and was more effective for differentiation than the D1/D2 region.
Conclusions:
- Genetic characterization supports the effective differentiation of Taphrina species, particularly using the ITS region.
- Molecular phylogenetics can correlate species clusters with host plant families and aid in disease diagnosis.