2 + 3: endosymbiosis Flashcards
what % of all extant plants show this type of symbiosis?
80%
what sort of symbiosis does mycorrhizal show?
endosymbiosis
what are glomerales?
arbuscular mycorrhizas producing widespread symbiosis
what 3 points can be concluded when you map the evolution of fungus onto the tree of life?
- mycorrhizal fungi evolved at a similar time to vascular plants
- all groups except mosses for mycorrhizal association
- predate evolution of roots
describe the example for evidence of arbuscular glomerales of ancient volcanic systems
rhynie- hot spring system with silicate rich water
- plants growing here inundated by silicate and often turn to stone
- fossil evidence of AMF fungus preserved at cellular scale
- aglaophyton major found which is homologous to modern day arbuscules
what is the interfacial apoplast and the theory of biological market?
- fungal cells push through cell membrane so it expands
- divides into hundreds of lobes covered in membrane forming interfacial apoplast where resources are exchanged
- membrane bound transporter for nutrients out and C in from apoplast
- theory: mycorrhizal reciprocal change of nutrients and C and includes interactions of different classes of ‘traders’
what is the Kiers et al evidence for the theory of biological market in glomerales
2011
- gm carrots so no shoot and express C transporters on outside to feed myc. fungus
- fungal species used: G.intraradices + G.aggregatum
- radioactive sugar on roots to measure C flow
- P added to one
- C flow to fungus with P as had the nutrients to give to the plant
- radioactive P added to fungus: fungus allocates P to roots that could give it C
what is the Walder et al evidence for the theory of biological market in glomerales
2015
regulation resource exchange in arbuscular myc. symbiosis
- most plants want to be myc.
- some dont respond at all
- some respond to specific mycorrhizas
- reciprocity only in subset of symbionts under specific conditions
- resource exchange in the symbiosis determined by comp. for surplus resources, functional diversity, sink strength
what did cameron 2010 discover about mycorrhizal networks?
- most plants connected by many fungal species
- myc. plants can attack species that don’t contribute to myc. environment by releasing chemicals that stop other plants having root hairs so less efficient at nutrient uptake
relating to glomerales what did Rinaudo et al discover?
2010
biomass of weeds higher if no myc. present in environment (growth promotion in absence)
what is an example of how mycorrhizal can have non nutritional benefits
help fight pathogens by increasing plants immune system
what are Basidiomycota ? (5)
ectomycorrhizas
- form tree like myc. associations
- form ectomycorrhizas but are endosymbiont
- plant dependent on host fungus for nutrient uptake as pine root tips covered in dense mat of fungus
- fungal hyphae mine for nutrients
- fungus extends between cortical cells but does not penetrate the cell
what are Ascomycota?
ericoid mycorrhizas
- form fungal blobs and coils within cell
what did Leake discover 1995?
- 400 species have become myco-heterotrophs
- evolved to cheat mutualism deriving C and mineral nutrients, giving nothing in return
- plants lack chlorophyll but dont form connections to other plants
- nourished by forming parasitic associations with fungi
a) why are most definitions of saprophytic fungi untrue? (such as 2002 new atlas of british and irish flora and 2004 flowering plants of neotropics)
b) how is the myth debunked?
a) - none of described saprophytic plants in volumes derive C from decaying organic matter
- dependence of myco-heterotrophs on C from fungal partners ignored
- suppresses role of mycorrhizal mycelium supplying C from autotrophs
b) saprophytes don’t obtain C directly from decaying soil matter they obtain it through parasitising soil fungi
what are the 2 categories for the C source for fungi parasitized by myco-heterotrophic plants? (detail)
- myco-heterotroph: associations with fungi which gain C saprotrophically from organic matter
- epiparasite: fungi obtain C by forming mutualistic mycorrhizal symbioses with other autotrophic plants so are in tripartite symbiosis via shared fungal network
what did McKendrick discover in 2000?
if no fungus then plants can obtain C
myco-heterotrophy evolved in lower plants give 1 example (latin, common, classification, family, habitat)
- cryptothallus mirabilis
- ghostwort
- epiparasite of ectomycorrhizas
- Hepaticae (liverwort)
- wet woodlands
myco-heterotrophy evolved in dicotyledonous families- give an example in the Ericaceae family (latin, common, classification, habitat)
- monotropa hypopitys
- yellow birds nest
- epiparasite of ectomycorrhizas
- forest understory
myco-heterotrophy evolved in dicotyledonous families- give an example in the Burmanniaceae family (latin, classification, habitat)
- afrothismia baerae
- epiparasite of arbuscular mycorrhizas
- tropical forest
myco-heterotrophy evolved in dicotyledonous families- give an example in the Gentianaceae family (latin, common, classification, habitat)
- voyria corymbosa
- ghost plant
- epiparasite of arbuscular mycorrhizas
- forest understory
myco-heterotrophy evolved in monocotyledons families- give an example in the triuridaceae family (latin, classification, habitat)
- sciaphila tosaensis
- epiparasite of arbuscular mycorrhizas
- forest understory
myco-heterotrophy evolved in monocotyledons families- give an example in the corsiaceae family (latin, classification, habitat
- Arachnitis uniflora
- epiparasite of arbuscular mycorrhizas
- forest understory
myco-heterotrophy evolved in monocotyledons families- give 3 examples in the orchidaceae family (latin, common, classification, habitat
- neottia nidus-avis
- birds nest orchid
- epiparasite of ectomycorrhizas
- forest understory
- neottia nidus-avis
- cephalanthera damasonium
- white helleborine
- partial/full epiparasite of ectomycorrhizas
- forest understory
- cephalanthera damasonium
- corallorhiza trifida
- coral root orchid
- forest understory
- corallorhiza trifida
does parasitism occur in monocotyledons or dicotyledons?
dicotyledons and have higher abundance of myco-heterotrophs
give 6 physiological and morphological features of epiparasitic and myco-heterotrophic plants
- structural simplification as dependent on another organism
- leaves reduced to scales (monotopa +neottia) or absent (corallorhiza+voyria)
- roots reduced (neottia+corallorhiza)
- minute seeds dependent on symbiotic germination (most orchids and gentians)
- fungus triggered germination (orchids)
- no/little chlorophyll (epiparasites)
what did cameron discover about orchids in 2006 about delayed payback symbiosis? (5)
- green orchids allocate C to fungal partner as adult
- life stage dependent trophic switch
- most radioactive P remained in fungus
- lots of C made it to roots and shoots
- delayed payback means paying back when adult and may be evolutionary weakness
what can be used as a rough predictor of mycoheterotrophy ?
- myco-heterotrophic and epiparasitic pathways give 13C isotope signature to plant
- detect organism hierarchy based on C makeup as accumulate within hierarchy
- seen in green orchids
what was camerons study on orchids and ectomycorrhizal fungi 2009?
- fagus, cephalanthera, corallorhiza, neottia share the fungi with surrounding trees in a myc. network
- varied in photosynthetic ability
- varied in chlorophyll with orchids having a lot
- lots of C obtained parasitically as shared similar heavy C signature
- trapped orchid and tree seedling exposing to CO2 to see how much C take up
- photosynthetic capacity differed for leaved plants but not leafless
in camerons 2010 paper what is the overview/abstract? (3)
- arbusuclar mycorrhizal fungi (AMF) can induce shifts in host communities
- increase host plants nutrient uptake and growth and suppress non mycorrhizal competitor species
- could be used on weeds in agro-ecosystems
in camerons 2010 paper what are further details on AMF in agro-ecosystems? (6)
- parasitic plants may be used to restore degraded plant communities
- can lead to community level shifts in species composition
- can enhance crop nutrition
- weeds have lower biomass in presence of fungi
- ploughing and inorganic fertilisers not viable methods so enhance AMF
- some plants cheat fungi (in glomeralean, basidiomycetes, ascomycetes)
in camerons 2008 paper paper what is the intro/summary? (7)
- c cost of mycorrhiza in green orchid G.repens
- measure simultaneous bidirectional fluxes of C sources
- C transferred rapidly from fungus to plant at interfacial apoplast and detected in plant fungal respiration
- plant has c cost to maintain symbiosis but increased nutrient supply
- 10% plant species myco-heterotrophic
- more C passed from plant to fungus
- orchid mycorrhiza mutualistic
in camerons 2008 paper paper what is the results/discussion? (5)
- more C in roots
- downflow greater than upflow
- first full bidirectional c budget for myc associations
- adult G.repens and myc less mutualistic
- delayed payback: C invested by adult repaid by adult orchid but risk of cheating
in Kiers et al 2011 paper what was the abstract/intro? (5)
- AMF promote growth of ceratocarpus anernarius without enhanced P nutrition
- mycotrophic status of c.arenarius established
- AMF community stimulates growth and seed production
- c.arenarius crucial in erosion control and desert ecosystem rehabilitation
- AMF can promote seedling establishment in degraded ecosystems
in Kiers et al 2011 paper what was the results/discussion? (4)
- vesicles and hyphae no arbuscules
- p content and shoot biomass and seed number higher in myc. treated plants
- AM fungal community present with +ve effect on plant growth
- detect and reward fungal partners with more carbohydrates which will supply the roots with more nutrients
in the Leake et al paper 2010 what was discovered in the abstract and intro? (6)
- myc. associations with tulasnelloid fungi in 5 dactylorhiza species
- orchids associate with many fungi from different clades/families
- most operational taxonomic units found in 2 or more species (OTU)
- each orchid species associated with 5 different OTUs
- orchid species decline, they rely on pollination and myc. symbioses
- may be able to switch to different fungi under adverse conditions
in the Leake et al paper 2010 what was discovered in the discussion and results? (4)
- all plants showed myc. associations
- 80% orchids associated with more than one fungal OTU
- multiple fungi may increase nutrient uptake as different lineages can access different resources
- some OTUs common and others widespread
what is an endosymbiont and give 4 points
organism living within body or cells of another organism
- usually nutritional in basis
- range of organisms, plants, insects, humans
- human gut flora, rhizobia, aphid endosymbionts
- endosymbiotic theory
what does induction of a stable symbiosis require?
organisms to signal to each other
what is interspecific signalling?
- induction of stable symbiosis
- mycorrhizal factors produced by arbuscular mycorrhizal spores that signal at germination
- the factors can diffuse across plant membrane
- initiate root branching and enhance mycorrhizal colonisation
in terms of interspecific signalling why may root morphology change?
branching increases chance fungal partner can find plant tissue
what are strigolactones?
produced by plant roots and induce hyphal branching which enhance mycorrhizal colonisation so act as interspecific signals
what is rhizobium?
(diazotroph)
- n fixing bacteria in the soil
- paraphyletic group with alpha and beta proteobacteria
- most common in legumes
- the bacteria fix N in return for C and other nutrients
what family are the legumes in?
Fabaceae
what are the 7 steps for interspecific signalling in legumes?
- legumes signal to rhizobia via alkaloids
- alkaloids induce +ve chemotaxis in rhizobia
- alkaloids induce nod-factor production in rhizobia
- these are sent out into the soil and facilitate production of root nodules where bacteria live
- root hairs respond to receive bacteria
- bacteria form an infection thread
- a mature root nodule develops and attaches to the plant vascular system
myc. and nod factors share a common pathway- what separates the two processes?
evolution of the gene NSP1
- lead to nodulation and root branching in nod factors
- leads to root branching and mycorrhization for myc factors
why is the root nodule physiology effective?
provides environment with just enough O2 as bacteria are aerobic
- too much O2 cant fix N
what happens to bacteroids when the root has a determinate nodule vs. indeterminate?
determinate- bacteroids survive
indeterminate- die and rhizobia escape the infection threads
what is leghaemoglobin?
- red
- buffers O2 levels in nodule so are optimal for N2 fixation as that can only occur at low O2 levels
what is the activity of nitrogenase enzyme used by rhizobia sensitive to and what is needed by rhizobia?
sensitive to O2
some of the O2 needed by rhizobia
what is the tragedy of the commons?
there are lots of different endosymbiont genotypes so a massive selection pressure
- if one cheats then they steal fitness
what did Kiers et al 2003 find in terms of mutualism regulation by forcing one subset to cheat?
- roots given N or Ar
- one forced to cheat plant downregulates energy to nodules of fewer bacteria in these roots
- plant reduces O2 below min needed to survive and reproduce in those that cheat
- punishes non contributing symbionts by reducing O2 to sub optimum for bacteria growth
what are bacteriocytes?
found in pea aphids
- specialised host cells that house the bacteria
how does the pea aphid feed? (3)
- inserts stylet into plant cells and probes for the phloem
- detects chemistry of phloem which is mainly sugar
- lacks many aphid essential amino acids
what is the endosymbiotic relationship in aphids?
aphid has Buchnera endosymbiont that synthesises amino acids, such as tryptophan, in return for carbohydrates
- can feed offspring with bacterial symbiont
what type of symbiont are they and what does this mean for their genes and genome?
obligate symbionts
- lost many free living genes
- genome size reduced as gets rid of genes it doesn’t need as DNA expensive
- increase in genes encoding amino acids
- reliant upon host
does the xylem or the phloem have more inorganic and organic N?
the xylem
what is inorganic N and organic?
inorganic: NH4+
organic: amino acids
what did Sasaki et al discover about pea aphid growth with and without endosymbionts in 1991?
- much more successful growth with symbiont
- success locked bacteria and aphids together
- origins of new aphid species lead to origins of new bacteria: phylogenetic congruence
what did Lynn margulis suggest?
the endosymbiont theory - that endosymbionts evolve into cell organelles
give features of organelles that were once endosymbionts?
- reduced genomes
- most genes transferred to host cell genome
- transport mechanism needed to move essential resources such as proteins to organelle
- host cell assumes control of organelles cell division
how are new mitochondria and plastids/chloroplasts formed?
process similar to binary fission (prokaryote like)
how many membranes do mitochondria and plastids have?
surrounded by 2 or more
- innermost shows compositional differences from other membranes in cell
- can act as transporters
what is mitochondria and plastid DNA like?
different from that of nucleus and similar to that of the bacteria
what is the internal structure and biochemistry of plastids similar to and which parts?
thylakoids and chlorophyll similar to cyanobacteria
what does mitochondria have thats similar to bacteria?
several enzymes and transport systems
what in the nucleus may be transported to the organelle?
proteins encoded at the nucleus
what are all chloroplasts descended from?
one major primary endosymbiotic event
essentially what are plants in simple terms?
complex and specialized algae
what did multiple secondary endosymbiotic events lead to?
complex organelles and diatoms
what did multiple tertiary endosymbiotic events lead to?
more complex dinoflagellates
what did Cameron et al discover in 2016 about paramecium busaria and endosymbiotic bacteria?
- it is a protist with an endosymbiotic relationship with algae
- gains nutrients from eating bacteria and can give them to algae who gives it C
- symbiotic responds strongly to light
- if restrict food then reduced density of symbiont
