title: Laser capture microdissection of uredinia formed by Melampsora larici-populina revealed a transcriptional switch between biotrophy and sporulation.
abstract: The foliar rust caused by the basidiomycete Melampsora larici-populina is the main disease affecting poplar plantations in Europe. The biotrophic status of rust fungi is a major limitation to study gene expression of cell or tissue types during host infection. At the uredinial stage, infected poplar leaves contain distinct rust tissues such as haustoria, infection hyphae, and uredinia with sporogenous hyphae and newly formed asexual urediniospores. Laser capture microdissection (LCM) was used to isolate three areas corresponding to uredinia and subjacent zones in the host mesophyll for expression analysis with M. larici-populina whole-genome exon oligoarrays. Optimization of tissue preparation prior to LCM allowed isolation of RNA of good integrity for genome-wide expression profiling. Our results indicate that the poplar rust uredinial stage is marked by distinct genetic programs related to biotrophy in the host palisade mesophyll and to sporulation in the uredinium. A strong induction of transcripts encoding small secreted proteins, likely containing rust effectors, is observed in the mesophyll, suggesting a late maintenance of suppression of host defense in the tissue containing haustoria and infection hyphae. On the other hand, cell cycle and cell defense rescue transcripts are strongly accumulated in the sporulation area. This combined LCM-transcriptomic approach brings new insights on the molecular mechanisms underlying urediniospore formation in rust fungi.
authors.affiliation: Unité Mixte de Recherche 1136 INRA/Nancy Université Interactions Arbres/Micro-organismes, Champenoux, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Hacquard
authors.forename: Christine
authors.initials: C
authors.lastname: Delaruelle
authors.forename: Valérie
authors.initials: V
authors.lastname: Legué
authors.forename: Emilie
authors.initials: E
authors.lastname: Tisserant
authors.forename: Annegret
authors.initials: A
authors.lastname: Kohler
authors.forename: Pascal
authors.initials: P
authors.lastname: Frey
authors.forename: Francis
authors.initials: F
authors.lastname: Martin
authors.forename: Sébastien
authors.initials: S
authors.lastname: Duplessis
mesh_terms: D001487:Basidiomycota / Q000502:physiology*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D042282:Microdissection / Q000379:methods*; D032107:Populus / Q000382:microbiology*; D013171:Spores, Bacterial; D014158:Transcription, Genetic
chemical_list: D005656:Fungal Proteins