Host-pathogen coevolution through trade-offs and coinfection

At the very core of the evolution of living organisms lie interactions with other species. Between two coevolving species, a change in one species may generate selection for a change in the other species. In host-pathogen coevolution the central dilemma is to understand how infectivity and virulence evolve. Infectivity is the ability to infect a given host while virulence is the harm the pathogen causes to its host, and therefore they determine the outcome of the interaction between the host and the pathogen. The emergence of new highly virulent pathogen species (e.g. Ash dieback pathogen Hymenoscyphus pseudoalbidus) and single pathogen strains (e.g. Ug99 of wheat stem rust pathogen Puccinia graminis f. sp. tritici) underline the urgent need for a deeper understanding of how virulence evolves. The aim of my thesis is to understand how life-history trade-offs and coinfection where two or more strains of the same pathogen are infecting the same host - are driving host-pathogen coevolution, and how these evolutionary trajectories translate to ecological dynamics in a metapopulation context using the Plantago lanceolata Podosphaera plantaginis interaction as a model system. The study approach ranged from the molecular level to population and metapopulation levels. I studied natural populations of P. lanceolata and P. plantaginis in the Åland islands to measure prevalence of coinfection and its consequences for disease epidemics in the wild. I also investigated variation in resistance in the natural host populations as well as the efficiency and costs of different plant resistance strategies in a common garden setting. Context dependence of evolutionary trade-offs were investigated by accounting for some of the spatial and temporal complexity of the natural pathogen metapopulation. Pathogen life-history trade-offs were studied in the context of local adaptation and costs of resistance in the perennial host were measured across multiple seasons. The pathogen s host exploitation versus transmission strategies were examined on relevant epidemiological time scales to understand factors creating heterogeneity in transmission dynamics. Key findings of the thesis include detection of high, yet variable levels of coinfection across the pathogen metapopulation, with more devastating epidemics measured in populations with higher levels of coinfection. This suggests a major role for coinfection in driving disease dynamics in natural populations. In the dynamic pathogen metapopulation, local adaptation mediates pathogen life history trade-offs and resistance polymorphism can be maintained through costs of resistance and changes in resource allocation under infection. In conclusion, this work contributes to our understanding of the drivers of evolution and maintenance of variation in the host and pathogen populations by linking evolutionary theory with empirical findings.Vuorovaikutus toisten lajien kanssa on eliöiden evoluution ytimessä. Muutos yhden lajin ominaisuuksissa voi aiheuttaa valintapainetta vastavuoroiseen muutokseen toisessa lajissa. Isännän ja taudinaiheuttajan yhteisevoluutiossa keskeinen kysymys on taudinaiheutuskyvyn ja virulenssin evoluutio. Virulenssi on taudinaiheuttajan isännälleen aiheuttamaa haitta ja yhdessä taudinaiheutuskyvyn kanssa nämä ominaisuudet määrittävät tautien tuhovoiman. Uusien tuhovoimaisten taudinaiheuttajalajien (esim. saarnensurma, Hymenoscyphus pseudoalbidus) ja kantojen (esim. mustaruosteen Puccinia graminis f. sp. tritici kanta Ug99) nouseminen korostaa tarvetta tautien evoluution parempaan ymmärtämiseen. Väitöskirjani tarkoitus on ymmärtää kuinka elinkierto-ominaisuuksien vaihtokauppasuhteet sekä yhteisinfektio kahden tai useamman saman taudinaiheuttajan kannan tartunta samalla isäntäyksilöllä ohjaavat isännän ja taudinaiheuttajan evoluutiota, sekä sitä miten näiden evolutiivinen kehitys näkyy ekologisessa dynamiikassa metapopulaatiokontekstissa käyttäen mallina heinäratamon ja härmäsienen (Plantago lanceolata Podosphaera plantaginis) välistä vuorovaikutusta. Tutkimukseni ylsi molekyylitasolta metapopulaatiotasolle. Tutkin yhteisinfektion yleisyyttä ja vaikutusta epidemioihin heinäratamon ja härmän luonnonpopulaatioissa Ahvenanmaalla. Lisäksi tarkastelin isäntäkasvin vastustuskyvyn vaihtelua luonnonpopulaatioissa. Pystytin monivuotisia puutarhakoeruutuja, joiden avulla selvitin isäntäkasvin iän ja vastustusstrategian vaikutusta taudin määrään sekä mahdollisia elinkiertokustannuksia, joita korkeasta vastustuskyvystä aiheutuu. Tämän lisäksi tutkin härmäpopulaatioiden luontaista vaihtelua, sekä selvitin tartutuskokeilla mahdollisia mekanismeja, jotka ylläpitävät tätä vaihtelua. Kasvukauden mittaisessa kokeessa selvitin miten yhteisinfektio vaikuttaa taudin leviämiseen kasvien välillä, sekä taudin leviämiseen vaikuttavia tekijöitä saman isäntäkasvin sisällä verrattuna itiöiden leviämiseen uusille isäntäkasveille. Tämän väitöskirjan keskeisiä tuloksia ovat korkeat, joskin vaihtelevat yhteisinfektion tasot härmän metapopulaatiossa sekä tuhovoimaisempien epidemioiden havaitseminen populaatioissa, joissa esiintyi eniten yhteisinfektiota. Tulosten perusteella yhteisinfektio on keskeisessä roolissa luonnonpopulaatioiden tautidynamiikassa. Tulokset osoittivat paikallisen sopeutumisen muokkaavan taudinaiheutuskyvyn ja itiöimisen suhdetta, sekä antoivat viitteitä niiden vaikutuksesta uusien tautipopulaatioiden syntymiseen ja kasvuun. Isännän vastustuskyvyn monimuotoisuutta ylläpitävät osaltaan vastustuskyvyn kustannukset sekä resurssien uudelleen allokointi infektion aikana. Kokonaisuudessaan tämä työ edistää evoluutioon sekä tauti- ja isäntäpopulaatioiden monimuotoisuuden ylläpitoon vaikuttavien tekijöiden parempaa ymmärtämistä yhdistämällä evolutiivista teoriaa ja empiirisiä tuloksia epidemiologiaa

Effect of maternal infection on progeny growth and resistance mediated by maternal genotype and nutrient availability

1. Maternal effects of pathogen infection on progeny development and disease resistance may be adaptive and have important consequences for population dynamics. However, these effects are often context-dependent and examples of adaptive transgenerational responses from perennials are scarce, although they may be a particularly important mechanism generating variation in the offspring of long-lived species. 2. Here, we studied the effect of maternal infection of Plantago lanceolata by Podosphaera plantaginis, a fungal parasite, on the growth, flower production and resistance of the progeny of six maternal genotypes in nutrient-rich and nutrient-poor environments. For this purpose, we combined a common garden study with automated phenotyping measurements of early life stages, and an inoculation experiment. 3. Our results show that the effects of infection on the mother plants transcend to impact their progeny. Although maternal infection decreased total leaf and flower production of the progeny by the end of the growing season, it accelerated early growth and enhanced resistance to the pathogen P. plantaginis. 4. We also discovered that the effects of maternal infection affected progeny development and resistance through a three way-interaction between maternal genotype, maternal infection status and nutrient availability. 5. Synthesis. Our results emphasize the importance of maternal effects mediated through genotypic and environmental factors in long-living perennials and suggest that maternal infection can create a layer of phenotypic diversity in resistance. These results may have important implications for both epidemiological and evolutionary dynamics of host-parasite interactions in the wild.Peer reviewe

Coinfection with a virus constrains within-host infection load but increases transmission potential of a highly virulent fungal plant pathogen

The trade-off between within-host infection rate and transmission to new hosts is predicted to constrain pathogen evolution, and to maintain polymorphism in pathogen populations. Pathogen life-history stages and their correlations that underpin infection development may change under coinfection with other parasites as they compete for the same limited host resources. Cross-kingdom interactions are common among pathogens in both natural and cultivated systems, yet their impacts on disease ecology and evolution are rarely studied. The host plant Plantago lanceolata is naturally infected by both Phomopsis subordinaria, a seed killing fungus, as well as Plantago lanceolata latent virus (PlLV) in the angstrom land Islands, SW Finland. We performed an inoculation assay to test whether coinfection with PlLV affects performance of two P. subordinaria strains, and the correlation between within-host infection rate and transmission potential. The strains differed in the measured life-history traits and their correlations. Moreover, we found that under virus coinfection, within-host infection rate of P. subordinaria was smaller but transmission potential was higher compared to strains under single infection. The negative correlation between within-host infection rate and transmission potential detected under single infection became positive under coinfection with PlLV. To understand whether within-host and between-host dynamics are correlated in wild populations, we surveyed 260 natural populations of P. lanceolata for P. subordinaria infection occurrence. When infections were found, we estimated between-hosts dynamics by determining pathogen population size as the proportion of infected individuals, and within-host dynamics by counting the proportion of infected flower stalks in 10 infected plants. In wild populations, the proportion of infected flower stalks was positively associated with pathogen population size. Jointly, our results suggest that the trade-off between within-host infection load and transmission may be strain specific, and that the pathogen life-history that underpin epidemics may change depending on the diversity of infection, generating variation in disease dynamics.Peer reviewe

Diverse and variable virus communities in wild plant populations revealed by metagenomic tools

Wild plant populations may harbour a myriad of unknown viruses. As the majority of research efforts have targeted economically important plant species, the diversity and prevalence of viruses in the wild has remained largely unknown. However, the recent shift towards metagenomics-based sequencing methodologies, especially those targeting small RNAs, is finally enabling virus discovery from wild hosts. Understanding this diversity of potentially pathogenic microbes in the wild can offer insights into the components of natural biodiversity that promotes long-term coexistence between hosts and parasites in nature, and help predict when and where risks of disease emergence are highest. Here, we used small RNA deep sequencing to identify viruses in Plantago lanceolata populations, and to understand the variation in their prevalence and distribution across the Aland Islands, South-West Finland. By subsequent design of PCR primers, we screened the five most common viruses from two sets of P. lanceolata plants: 164 plants collected from 12 populations irrespective of symptoms, and 90 plants collected from five populations showing conspicuous viral symptoms. In addition to the previously reported species Plantago lanceolata latent virus (PlLV), we found four potentially novel virus species belonging to Caulimovirus, Betapartitivirus, Enamovirus, and Closterovirus genera. Our results show that virus prevalence and diversity varied among the sampled host populations. In six of the virus infected populations only a single virus species was detected, while five of the populations supported between two to five of the studied virus species. In 20% of the infected plants, viruses occurred as coinfections. When the relationship between conspicuous viral symptoms and virus infection was investigated, we found that plants showing symptoms were usually infected (84%), but virus infections were also detected from asymptomatic plants (44%). Jointly, these results reveal a diverse virus community with newly developed tools and protocols that offer exciting opportunities for future studies on the eco-evolutionary dynamics of viruses infecting plants in the wild.Peer reviewe

Genetic analysis reveals long-standing population differentiation and high diversity in the rust pathogen Melampsora lini

A priority for research on infectious disease is to understand how epidemiological and evolutionary processes interact to influence pathogen population dynamics and disease outcomes. However, little is understood about how population adaptation changes across time, how sexual vs. asexual reproduction contribute to the spread of pathogens in wild populations and how diversity measured with neutral and selectively important markers correlates across years. Here, we report results from a long-term study of epidemiological and genetic dynamics within several natural populations of theLinum marginale-Melampsora liniplant-pathogen interaction. Using pathogen isolates collected from three populations of wild flax (L.marginale) spanning 16 annual epidemics, we probe links between pathogen population dynamics, phenotypic variation for infectivity and genomic polymorphism. Pathogen genotyping was performed using 1567 genome-wide SNP loci and sequence data from two infectivity loci (AvrP123,AvrP4). Pathogen isolates were phenotyped for infectivity using a differential set. Patterns of epidemic development were assessed by conducting surveys of infection prevalence in one population (Kiandra) annually. Bayesian clustering analyses revealed host population and ecotype as key predictors of pathogen genetic structure. Despite strong fluctuations in pathogen population size and severe annual bottlenecks, analysis of molecular variance revealed that pathogen population differentiation was relatively stable over time. Annually, varying levels of clonal spread (0-44.8%) contributed to epidemics. However, within populations, temporal genetic composition was dynamic with rapid turnover of pathogen genotypes, despite the dominance of only four infectivity phenotypes across the entire study period. Furthermore, in the presence of strong fluctuations in population size and migration, spatial selection may maintain pathogen populations that, despite being phenotypically stable, are genetically highly dynamic. Author summary Melampsora liniis a rust fungus that infects native flax,Linum marginalein south-eastern Australia where its epidemiology and evolution have been intensively studied since 1987. Over that time, substantial diversity in the pathotypic structure ofM.linihas been demonstrated but an understanding of how genetic diversity in pathogen populations is maintained through space and time is lacking. Here we integrated phenotypic, genotypic and epidemiological datasets spanning 16 annual epidemics across three host populations to examine long-term pathogen genetic dynamics. The results show that host ecotype is the dominant selective force in the face of strong bottlenecks and annual patterns of genetic turnover. Results from previous studies indicate that in this geographic region,M.linilacks the capacity to reproduce sexually-we thus expected to find limited genetic diversity and evidence for strong clonality influencing genetic dynamics within growing seasons. However, the breadth of genomic coverage provided by the SNP markers revealed high levels of genotypic variation withinM.linipopulations. This discovery contrasts with observed phenotypic dynamics as the epidemics of this pathogen were largely dominated by four pathotypes across the study period. Based on a detailed assessment and comparison of pathotypic and genotypic patterns, our study increases the understanding of how genetic diversity is generated and maintained through space and time within wild pathogen populations. The implications for the management of resistance to pathogens in agricultural or conservation contexts are significant: the appearance of clonality may be hiding high levels of pathogen diversity and recombination. Understanding how this diversity is generated could provide new and unique ways to mitigate or suppress the emergence of infectious strains, allowing to efficiently combat harmful diseases.Peer reviewe

Co-infection alters population dynamics of infectious disease

Co-infections by multiple pathogen strains are common in the wild. Theory predicts co-infections to have major consequences for both within- and between-host disease dynamics, but data are currently scarce. Here, using common garden populations of Plantago lanceolata infected by two strains of the pathogen Podosphaera plantaginis, either singly or under co-infection, we find the highest disease prevalence in co-infected treatments both at the host genotype and population levels. A spore-trapping experiment demonstrates that co-infected hosts shed more transmission propagules than singly infected hosts, thereby explaining the observed change in epidemiological dynamics. Our experimental findings are confirmed in natural pathogen populations-more devastating epidemics were measured in populations with higher levels of co-infection. Jointly, our results confirm the predictions made by theoretical and experimental studies for the potential of co-infection to alter disease dynamics across a large host-pathogen metapopulation.Peer reviewe

KANSAINVÄLINEN PROJEKTI JA TIETOKANTA "EURASIAN LUONNOLLINEN REKISTERÖINTI" ESIMERKKIÄ LAAJAMITTAISESTA YMPÄRISTÖTUTKIMUKSEN INTEGROINTIIN EURASIAAN TAIGA BIOM:N PUHTEESSA

Proceedings on itse nimi englanninkielellä, mutta sisältö on eri kielellä (venäjä, englanti, ukraina), sen takia on erönlainen kieli sekannusNon peer reviewe

In-vitro studies on antioxidant and antidiabetic potential of Sesoot (Garcinia picrorrhiza Miq.) fruit ethanolic extract from Indonesia

Diabetes mellitus (DM) is a disease that can be identified by high levels of blood glucose. Garcinia plants have been widely used for many traditional medicines as antioxidant, anticancer, antidiabetics, and antiinflammation. The antioxidant and antidiabetic activities of (Garcinia picrorrhiza Miq.) or sesoot fruit extract were evaluated in this study and compared with xanthone. The antioxidant and antidiabetic of ethanolic ripe sesoot (G. picrorrhiza Miq.) fruit extract (GpKar) was evaluated by (ABTS) reducing activity, α-glucosidase, β-glucosidase, and α-amylase inhibitor activity. GpKar showed higher ABTS-reducing activity (IC50 = 49.30 µg/mL) than xanthone (IC50 = 404.30 µg/mL). GpKar showed IC50 = 109.32 µg/mL for α-glucosidase inhibitory activity, while xanthones had a better activity (IC50 = 33.97 µg/mL). GpKar also showed lower α-amylase inhibitory activity and  β-glucosidase (IC50 = 126.01 and 9432.09 µg/mL) compared to xanthone (IC50 = 44.32 and 405.03 µg/mL, respectively). The compounds of GpKar are proven to have antioxidant and antidiabetic activities. Therefore, it will be industrially relevant to develop a natural medicine for decreasing DM risk, thus evaluating the antioxidant and antidiabetic effect of G. picrorrhiza by a pre-clinic study is needed