Transcriptome analysis of enriched Golovinomyces orontii haustoria by deep 454 pyrosequencing
Ralf Weßling1, Sarah M Schmidt, Cristina O Micali
1Max-Planck-Institute for Plant Breeding Research, Department of Plant-Microbe Interactions, Carl-von-Linné-Weg 10, 50829 Cologne, Germany.
Abstract:
Powdery mildews are phytopathogenic ascomycetes that have an obligate biotrophic lifestyle and establish intimate relationships with their plant hosts. A crucial aspect of this plant-fungus interaction is the formation of specialized fungal infection structures termed haustoria. Although located within the cell boundaries of plant epidermal cells, haustoria remain separated from the plant cytoplasm by a host plasma membrane derivative, the extrahaustorial membrane. Haustoria are thought to represent pivotal sites of nutrient uptake and effector protein delivery. We enriched haustorial complexes from Arabidopsis thaliana plants infected with the powdery mildew fungus Golovinomyces orontii and performed in-depth transcriptome analysis by 454-based pyrosequencing of haustorial cDNAs. We assembled 7077 expressed sequence tag (EST) contigs with greater than 5-fold average coverage and analyzed these with regard to the respective predicted protein functions. We found that transcripts coding for gene products with roles in protein turnover, detoxification of reactive oxygen species and fungal pathogenesis are abundant in the haustorial EST contigs, while surprisingly transcripts encoding presumptive nutrient transporters were not highly represented in the haustorial cDNA library. A substantial proportion (∼38%) of transcripts coding for predicted secreted proteins comprises effector candidates. Our data provide valuable insights into the transcriptome of the key infection structure of a model obligate biotrophic phytopathogen.
Insights
This study reveals the transcriptome of powdery mildew haustoria, key fungal infection structures. Abundant transcripts relate to pathogenesis and protein turnover, with many effector candidates, but fewer nutrient transporters than expected.
Area of Science:
- Plant Pathology
- Mycology
- Molecular Biology
Background:
- Powdery mildews are obligate biotrophic fungi that infect plants.
- Haustoria are specialized fungal structures essential for nutrient uptake and effector delivery.
- Understanding haustorial function is crucial for plant-fungus interactions.
Purpose of the Study:
- To analyze the transcriptome of haustoria from Golovinomyces orontii infecting Arabidopsis thaliana.
- To identify genes and functions active within these crucial infection structures.
Main Methods:
- Enrichment of haustorial complexes from infected Arabidopsis plants.
- Transcriptome analysis using 454-based pyrosequencing of haustorial cDNAs.
- Assembly and functional analysis of expressed sequence tag (EST) contigs.
Main Results:
- 7077 EST contigs were assembled with high coverage.
- Abundant transcripts involved in protein turnover, reactive oxygen species detoxification, and pathogenesis.
- Approximately 38% of predicted secreted proteins are potential effector candidates.
- Surprisingly few transcripts for nutrient transporters were identified.
Conclusions:
- The haustorial transcriptome is rich in pathogenesis-related genes and effector candidates.
- This provides insights into the molecular mechanisms of obligate biotrophic fungal infection.
- The low abundance of nutrient transporter transcripts warrants further investigation.
