1、,Three Clonal Lineages of Phytophthora cinnamomi in Australia Revealed by MicrosatellitesM.P Dobrowolski et al., Phytopathology 2002,Todays talk:,Overview of P. cinnamomi and its impact in Western Australia General biology How does an introduced pathogen evolve Use of microsatellites Reveals limited
2、 introductions, but changes are occurring through mitosis,Phytophthora cinnamomi,Oomycete (Kingdom Chromista, brown algae) Genus Phytophthora has 50 spp. Heterothallic (requires 2 mating types for sex) Soilborne pathogen- infects roots/stem collars Present in 67 countries Isolated from 1000 plant sp
3、p. Introduced pathogen to Australia in early 1900s,P. cinnamomi in Western Australia,Causes disease “jarrah dieback” 1921 first jarrah deaths; 1964 deaths shown to be caused by P. cinnamomi. Predominantly A2 mating type,Impact Natural Ecosystems,Between 8-9,000 plant species in south-west of Western
4、 Australia Approximately 2000 species are susceptible to Phytophthora cinnamomi Indirect effects of P. cinnamomi on plant and animal communities is unknown,P. cinnamomi distribution,How is it spread?,Natural root contact, free draining water (warm spring, summer & early autumn) Artificial transport
5、of infested soil (tyres, road making) hikers (boots, tent pegs & toilet trowels) planting infected nursery stock,Goals of the study,Previously reported using isozymes that there is limited genetic variability Authors developed microsatellite markers (different alleles identified by different length
6、of PCR amplicon) Does microsatellite analysis confirm low genetic diversity Is there sex? Is there variation without sex, and if so what does it tell us,Materials and Methods,Sample intensively in Western Australia Run microsatellites How many genotypes they found in Western Aiustralia Are alleles i
7、n linkage disequilibrium Are Western Australia genotypes found in the rest of the world? Is linkage disequilibrium the same What kind of allelic variation is there and what does it imply,Results-1,Only three genotypes found (limited variability)Three genotypes occupy distinct areas but with some ver
8、lapThey carry distinct mating allelesThere are a variants, with alleles slightly differentVariants are clustered,Results-2,Index of association indicates that alleles are co-segregatingCosegregation indicates no sex, but mitotic recombinationClustering of variants suggests these are arising locally
9、(if they were separate introductions they would be all over)There are a variants, with alleles slightly differentMitotic crossing over explains variants and LOH,Results-3,Same genotypes of WA found in Eastern Australia and in other parts of the worldOther genotypes, clearly different and generated b
10、y sex, also present, especially in PNGClustering of variants suggests these are arising locally (if they were separate introductions they would be all over),CONCLUSION,Limited variability in spite the fact that both mating types are present indicates no sex (confirmed by Ia) There is diversity creat
11、ed locally by mitotic recombination Proof that it is being moved around the world,IMPLICATIONS,Need to stop worldwide movement of this pathogen In Western Australia need to prevent local movement, because both mating types are present There is local adaptation through mitosis, one more reason to avo
12、id even local movement of strains,Summary of first class,Undertanding of nature, an essential part of cultureForests essential for life on the planetFungi essential for survival of forests,Summary of second class,DNA mutates, evolves, and different DNA sequences can be assigned to different individu
13、als, populations from different provenances, closely related species, different species, different microbial pathovarsDNA-based phylogeography allowed to discover pine pathogen in Italy was of North American originDNA based genealogies allowed to identify hybridization between native and exotic path
14、ogenDNA allows to identify new species and to determine whether they are exotic or not,Definitions,Propagule= structure used by an organism to spread or survive Locus= a physical portion of a chromosome,a gene Intron= a portion of DNA , a locus that does not code for a protein Exon= a coding gene,De
15、finitions-2,Alleles= different DNA sequences at the same locus If a locus has variation in sequence it is polymorphic (many forms) Polymorphisms are differences in DNA among organisms, the more polymorphisms the easier it is to differentiate organisms There are more polymorphisms in introns,Definiti
16、ons-3,Invasive organisms: exotic organism that reproduces and occupies progressively a larger area: Fast reproductive cycle Vectored Hardy Occupy unoccupied niches Different drain on natural resources Make environment favorable for itself and other invaders Linked to disturbances If pathogen , more
17、changes because top of pyramid May hybridize with native species: new taxon is created,Summary of second class,DNA mutates, evolves, and different DNA sequences can be assigned to different individuals, populations from different provenances, closely related species, different species, different mic
18、robial pathovarsDNA-based phylogeography allowed to discover pine pathogen in Italy was of North American originDNA based genealogies allowed to identify hybridization between native and exotic pathogenDNA allows to identify new species and to determine whether they are exotic or not,Definitions,Alt
19、ernatively fixed allelesDominant vs. co-dominant markersGenotype,Summary of fourth lesson,ASCOMYCETES, BASIDIOMYCETES, OOMYCETESDISEASE TRIANGLE+ humansDominant/CO-Dominant/ Genotype,Summary of sixth lesson,Janzen-Connol hypothesis; explanation of why diseases lead to spatial heterogeneityDiseases a
20、lso lead to heterogeneity or changes through time Driving succession The Red Queen Hypothesis: selection pressure will increase number of resistant plant genotypesCo-evolution: pathogen increase virulence in short term, but in long term balance between host and pathogen Density dependance,Summary of
21、 fifth lesson,Disease as “disease triangle”, effect of humans, disease as pant-microbe interactionDifferent types of disease of wild plantsTrue effect of disease: fertility+mortality+indirect effect on pollinators+unfair competitive advantage.but what about the “ carry over effect” Density dependanc
22、e,Summary of sixth lesson,Janzen-Connol hypothesis; explanation of why diseases lead to spatial heterogeneityDiseases also lead to heterogeneity or changes through time Driving succession The Red Queen Hypothesis: selection pressure will increase number of resistant plant genotypesCo-evolution: path
23、ogen increase virulence in short term, but in long term balance between host and pathogenComplexity of forest diseases: primary vs. secondaruy, modes of dispersal etc,Summary of seventh lesson,SEX; the great homogenizing force, and also ability to create new allelesINTERSTERILITY/ MATING SOMATIC COM
24、PATIBILITYNEED TO USE MULTIPLE MARKERS; SC does that, otherwise go to molecular markersPCR/ RAPDS,Summary of 8th lesson,Exotic microbes have a reduced level of genetic variabilityIf genotypes fall on clades separated by long branches, it may be an indication there is no sex going on between individu
25、als belonging to the two branches. Formal tests like the Index of association can test for thatAnonymous multilocus analysis can be done without any knowledge of the genome using markers such as RAPDs or AFLPsNeed to eliminate co-segregant markers and to use Jaccard;s,Molecular Markers,DNA genotypin
26、g,HOW CAN WE DETERMINE IF THEY ARE RELATED?,By using random genetic markers we find out the genetic similarity among these genotypes infecting adjacent trees is highIf all spores are generated by one individual They should have the same mitochondrial genome They should have one of two mating alleles
27、,HOW TO DETERMINE WHETHER DIFFERENT SITES BELONG TO THE SAME POP OR NOT?,Sample the sites and run the genetic markersIf sites are very different:All individuals from each site will be in their own exclusive clade, if two sites are in the same clade maybe those two populations actually are linked (within reach) In AMOVA analysis, amount of genetic variance among populations will be significant (if organism is sexual portion of variance among individuals will also be significant) F statistics: Fst will be over ) 0.10 (suggesting stongt structuring) There will be isolation by distance,
