Handbook Part 2 - International Mycological Association
Handbook Part 2 - International Mycological Association
Handbook Part 2 - International Mycological Association
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PS8-468-0434<br />
Evolution of microsatellites in the mitochondrial genome of Rhynchosporium secalis<br />
S Torriani 1, S Banke 3, C Linde 2, BA MacDonald 1<br />
1 Institute of Integrative Biology, Zurich, Zurich, Switzerland, 2 School of Botany and Zoology, Canberra, Australia, 3<br />
Biological Inst., Copenhagen, Denmark<br />
The aim of this project was to investigate the evolution of microsatellites in a mitochondrial genome, more specific to<br />
test hypothesis that the microsatellites evolve faster than the variable nucleotide regions and therefore could add to<br />
the diversity of the genome.<br />
Two variable microsatellite regions in the genome of Rhynchosporium secalis were identified. The microsatellite<br />
repeats consisted of 2 and 7 base-pair repeat respectively. For the two loci, four and three alleles were identified<br />
among 60 worldwide isolates of R. secalis. Variable flanking regions of the microsatellite and other variable regions of<br />
the mitochondrial genome were sequenced in order to infer a phylogeny representing the mitochondrial genome.<br />
No phylogenetic conflict was observed among the regions sequenced. All the sequence loci were therefore treated<br />
as one DNA sequence locus. A haplotype network was generated from the combined sequence data and a total of<br />
11 haplotypes was found. Only one missing haplotype was identified in the network, suggesting a good representation<br />
of the diversity found in the mitochondrial genome. After mapping the microsatellites onto the haplotype network, we<br />
found that one microsatellite increased the diversity in the haplotype network. The other microsatellite was responsible<br />
for a conflict by introducing homoplasy in the network, suggesting that the same microsatellite repeat number might<br />
have arisen twice. We conclude that the microsatellites found in the mitochondrial genome of R. secalis will be useful<br />
to analyse populations of R. secalis. It also suggests that the mutation rates for the microsatellites are higher than the<br />
nucleotide substitution rates in the mitochondrial genome.<br />
PS8-469-0439<br />
Population expansion-migration scenarios explain the demographic history of the fungal pathogen<br />
Mycosphaerella graminicola<br />
S Banke<br />
Biological Inst., Copenhagen, Denmark<br />
The following hypothesis was tested in this project: a population that evolve with a new host is likely to show high levels<br />
of population expansion over time, where as population recently founded by gene flow show no population<br />
expansion and a more disruptive phylogenetic network pattern.<br />
Five global populations of Mycosphaerella graminicola were chosen for this study and information from 6 DNA<br />
sequence loci and four microsatellite loci was used to estimate the different population genetic parameters and infer<br />
haplotype networks. Haplotype networks from recently founded populations showed more disruptive networks, where<br />
as the populations that potentially had evolved with the new host showed star like networks. Two different models<br />
were used to estimate mainly population expansion and migration, the first model allowed for recombination and<br />
estimated directional gene flow as well as possible growth for each population. The second model did not allow for<br />
any recombination, but estimated divergence time, migration and population expansion between two populations<br />
at the time. Both models supported the same scenarios where significant population expansion where seen in the<br />
populations evolving with the host and no expansion in the recently founded populations. The migration estimates<br />
helped to explain this pattern as most migration where coming from the populations evolving with the host to the<br />
recently founded populations. We conclude that population expansion might play an important role in shaping the<br />
population structure of a pathogen evolving on a new host, given that the new host is successful<br />
PS8-470-0444<br />
Origin And Expansion Of Rhynchosporium Secalis, A Fungal Leaf Pathogen Of Barley<br />
CC Linde 1, BA McDonald 2, PL Zaffarano 1<br />
1 School of Botany and Zoology, The Australian National University, Canberra, ACT, Australia, 2 Plant Pathology,<br />
Institute of Integrative Biology, ETH, Zurich, Switzerland<br />
Rhynchosporium secalis is a Deuteromycetous fungus with a proposed teleomorph in the Discomycetes. However, the<br />
teleomorph has never been found and its existence is solely based on observed moderate levels of neutral genetic<br />
diversity and frequency-dependent-selection on mating types as measured in some populations. It is a pathogen that<br />
infects cultivated barley and other Hordeum relatives as well as eg couch grass (Agropyron repens), a common grass<br />
species native to Eurasia. Because of its common association with cultivated barley, a coevolutionary relationship<br />
between Hordeum species and R. secalis is assumed, which suggest a Middle Eastern origin for R. secalis. However,<br />
neutral genetic variation in R. secalis, as obtained with RFLPs and 15 microsatellite loci, consistently reveal a significant<br />
lower number of alleles and lower levels of gene and genotypic diversity in R. secalis populations originating from<br />
cultivated barley in the Middle East, as well as from the non-cultivated Hordeum spontaneum populations from the<br />
Middle East, the progenitor of cultivated barley. This suggests that R. secalis did not co-evolve with barley, but coevolved<br />
with another host and only encountered barley when it was introduced as an agricultural crop.<br />
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