gabriela aguileta

Although parasitism is one of the most common lifestyles among eukaryotes, population
genetics on parasites lag far behind those on free-living organisms, probably
because they are rarely conspicuous in the environment, do not possess the visible
morphologic or behavioral variation used in the early studies of population genetics,
and are less charismatic than the macrofauna. However, the advent of molecular
markers offers great tools for studying key processes of parasite biology, such
as dispersal, mating systems, host adaptation, and patterns of speciation. Population
genetics studies have also valuable practical applications, for instance for studying
the evolution of drug resistance or new virulence. Another reason to study epidemiology
and evolution in parasites is that they display a huge diversity of life cycles
and lifestyles, thus providing great opportunity for comparative studies to test pathogen-
specific questions or general issues about evolution. Nevertheless, the field of
parasitology has yet to attract more evolutionary biologists. This is especially true
for fungal parasites, despite their importance in crop diseases, and even in animal
and human diseases. Furthermore, despite their obvious common interests there are
few connections so far between scientists working on fungal parasites versus other
parasites.

We report the development of 17 microsatellite markers in the cheese fungi Penicillium camemberti and P. roqueforti, using an enrichment protocol. Polymorphism and cross-amplification were explored using 23 isolates of P. camemberti, 26 isolates of P. roqueforti, and 2 isolates of each of the P. chrysogenum and P. nalgiovense species, used to produce meat fermented products. The markers appeared useful for differentiating species, both using their amplification sizes and the sequences of their flanking regions. The microsatellite locus PC4 was particularly suitable for distinguishing contaminant species closely related to P. camemberti and for clarifying the phylogenetic relationship of this species with its supposed ancestral form, P. commune. We analyzed 22 isolates from different culture collections assigned to the morphospecies P. commune, most of them occurring as food spoilers, mainly from the cheese environment. None of them exhibited identical sequences with the ex-type isolate of the species P. commune. They were instead distributed into two other distinct lineages, corresponding to the old species P. fuscoglaucum and P. biforme, previously synonymised respectively with P. commune and P. camemberti. The ex-type isolate of P. commune was strictly identical to P. camemberti at all the loci examined. P. caseifulvum, a non toxinogenic species described as a new candidate for cheese fermentation, also exhibited sequences identical to P. camemberti. The microsatellite locus PC4 may therefore be considered as a useful candidate for the barcode of these economically important species.

Numerous genes in diverse organisms have been shown to be under positive selection, especially genes involved in reproduction, adaptation to contrasting environments, hybrid inviability, and host-pathogen interactions. Looking for genes under positive selection in pathogens has been a priority in efforts to investigate coevolution dynamics and to develop vaccines or drugs. To elucidate the functions involved in host specialization, here we aimed at identifying candidate sequences that could have evolved under positive selection among closely related pathogens specialized on different hosts. For this goal, we sequenced c. 17 000–32 000 ESTs from each of four Microbotryum species, which are fungal pathogens responsible for anther smut disease on host plants in the Caryophyllaceae. Forty-two of the 372 predicted orthologous genes showed significant signal of positive selection, which represents a good number of candidate genes for further investigation. Sequencing 16 of these genes in 9 additional Microbotryum species confirmed that they have indeed been rapidly evolving in the pathogen species specialized on different hosts. The genes showing significant signals of positive selection were putatively involved in nutrient uptake from the host, secondary metabolite synthesis and secretion, respiration under stressful conditions and stress response, hyphal growth and differentiation, and regulation of expression by other genes. Many of these genes had transmembrane domains and may therefore also be involved in pathogen recognition by the host. Our approach thus revealed fruitful and should be feasible for many non-model organisms for which candidate genes for diversifying selection are needed.

Numerous genes in diverse organisms have been shown to be under positive selection, especially genes involved in reproduction, adaptation to contrasting environments, hybrid inviability, and host-pathogen interactions. Looking for genes under positive selection in pathogens has been a priority in efforts to investigate coevolution dynamics and to develop vaccines or drugs. To elucidate the functions involved in host specialization, here we aimed at identifying candidate sequences that could have evolved under positive selection among closely related pathogens specialized on different hosts. For this goal, we sequenced c. 17 000–32 000 ESTs from each of four Microbotryum species, which are fungal pathogens responsible for anther smut disease on host plants in the Caryophyllaceae. Forty-two of the 372 predicted orthologous genes showed significant signal of positive selection, which represents a good number of candidate genes for further investigation. Sequencing 16 of these genes in 9 additional Microbotryum species confirmed that they have indeed been rapidly evolving in the pathogen species specialized on different hosts. The genes showing significant signals of positive selection were putatively involved in nutrient uptake from the host, secondary metabolite synthesis and secretion, respiration under stressful conditions and stress response, hyphal growth and differentiation, and regulation of expression by other genes. Many of these genes had transmembrane domains and may therefore also be involved in pathogen recognition by the host. Our approach thus revealed fruitful and should be feasible for many non-model organisms for which candidate genes for diversifying selection are needed.

Numerous genes in diverse organisms have been shown to be under positive selection, especially genes involved in reproduction, adaptation to contrasting environments, hybrid inviability, and host-pathogen interactions. Looking for genes under positive selection in pathogens has been a priority in efforts to investigate coevolution dynamics and to develop vaccines or drugs. To elucidate the functions involved in host specialization, here we aimed at identifying candidate sequences that could have evolved under positive selection among closely related pathogens specialized on different hosts. For this goal, we sequenced c. 17 000–32 000 ESTs from each of four Microbotryum species, which are fungal pathogens responsible for anther smut disease on host plants in the Caryophyllaceae. Forty-two of the 372 predicted orthologous genes showed significant signal of positive selection, which represents a good number of candidate genes for further investigation. Sequencing 16 of these genes in 9 additional Microbotryum species confirmed that they have indeed been rapidly evolving in the pathogen species specialized on different hosts. The genes showing significant signals of positive selection were putatively involved in nutrient uptake from the host, secondary metabolite synthesis and secretion, respiration under stressful conditions and stress response, hyphal growth and differentiation, and regulation of expression by other genes. Many of these genes had transmembrane domains and may therefore also be involved in pathogen recognition by the host. Our approach thus revealed fruitful and should be feasible for many non-model organisms for which candidate genes for diversifying selection are needed.