title: SNP design from 454 sequencing of Podosphaera plantaginis transcriptome reveals a genetically diverse pathogen metapopulation with high levels of mixed-genotype infection.
abstract: BACKGROUND
  Molecular tools may greatly improve our understanding of pathogen evolution and epidemiology but technical constraints have hindered the development of genetic resources for parasites compared to free-living organisms. This study aims at developing molecular tools for Podosphaera plantaginis, an obligate fungal pathogen of Plantago lanceolata. This interaction has been intensively studied in the Åland archipelago of Finland with epidemiological data collected from over 4,000 host populations annually since year 2001.
  
  
  RESULTS
  A cDNA library of a pooled sample of fungal conidia was sequenced on the 454 GS-FLX platform. Over 549,411 reads were obtained and annotated into 45,245 contigs. Annotation data was acquired for 65.2% of the assembled sequences. The transcriptome assembly was screened for SNP loci, as well as for functionally important genes (mating-type genes and potential effector proteins). A genotyping assay of 27 SNP loci was designed and tested on 380 infected leaf samples from 80 populations within the Åland archipelago. With this panel we identified 85 multilocus genotypes (MLG) with uneven frequencies across the pathogen metapopulation. Approximately half of the sampled populations contain polymorphism. Our genotyping protocol revealed mixed-genotype infection within a single host leaf to be common. Mixed infection has been proposed as one of the main drivers of pathogen evolution, and hence may be an important process in this pathosystem.
  
  
  CONCLUSIONS
  The developed SNP panel offers exciting research perspectives for future studies in this well-characterized pathosystem. Also, the transcriptome provides an invaluable novel genomic resource for powdery mildews, which cause significant yield losses on commercially important crops annually. Furthermore, the features that render genetic studies in this system a challenge are shared with the majority of obligate parasitic species, and hence our results provide methodological insights from SNP calling to field sampling protocols for a wide range of biological systems.
authors.affiliation: Metapopulation Research Group, Department of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Tollenaere
authors.forename: Hanna
authors.initials: H
authors.lastname: Susi
authors.forename: Jussi
authors.initials: J
authors.lastname: Nokso-Koivisto
authors.forename: Patrik
authors.initials: P
authors.lastname: Koskinen
authors.forename: Ayco
authors.initials: A
authors.lastname: Tack
authors.forename: Petri
authors.initials: P
authors.lastname: Auvinen
authors.forename: Lars
authors.initials: L
authors.lastname: Paulin
authors.forename: Mikko J
authors.initials: MJ
authors.lastname: Frilander
authors.forename: Rainer
authors.initials: R
authors.lastname: Lehtonen
authors.forename: Anna-Liisa
authors.initials: AL
authors.lastname: Laine
mesh_terms: D001203:Ascomycota / Q000235:genetics* / Q000502:physiology*; D019143:Evolution, Molecular; D020869:Gene Expression Profiling; D005819:Genetic Markers / Q000235:genetics; D005838:Genotype; D054884:Host-Pathogen Interactions; D058977:Molecular Sequence Annotation; D009181:Mycoses / Q000382:microbiology*; D010943:Plantago / Q000382:microbiology; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D012331:RNA, Fungal / Q000235:genetics; D015203:Reproducibility of Results; D017423:Sequence Analysis, RNA
chemical_list: D005819:Genetic Markers; D012331:RNA, Fungal