eeb331-08 l17 glomero - university of...

Lecture 18

- Glomeromycota

- Mycorrhizal Associations

http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi

Glomeromycota(Vesicular) Arbuscular endomycorrhizal fungi, or (V)AM fungi

Mycorrhizal root system washed carefully from coarse sand to reveal theintact network with external hyphae (arrow) with spores (S) produced byGlomus mosseae. (bar = 100 um)

- small group of about 130 described morphological species;--- associated with ca. 300,000 plant species (ca. 80 - 90 % of of land plants);

- coenocytic hyphae ==> previously included in the Zygomycota, Order Glomales- multinucleate asexual spores can contain up to 5,000 nuclei.- sexual stage never observed in any member of the Glomales--- clonality?------ but extreme genetic variation of ribosomal DNA sequences is found within a single spore; still no datafor other genes; these organisms are difficult to work with at the molecular level.

- molecular data do not indicate monophyly between Zygomycota and Glomales---- Glomeromycota are probably sister group to Asco-Basidio==> the phylum Glomeromycota has been suggested by Schüssler et al., 2001.

- somatic hyphae are similar in all taxa.- little variation in the shape of arbuscules and vesicles (the latter not always present),- spores provide the most useful characteristics for differentiation of species.

More info from: http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi

Glomeromycota(Vesicular) Arbuscular endomycorrhizal fungi, or (V)AM fungi


Structures in Soil- Hyphae - A network of hyphae forms in the soilwith thicker hyphae which function as conduits andthin branched hyphae which are thought to absorbnutrients.- Spores - Large (for a fungus) asexual sphericalstructures (20-1000+ um diameter) that form onhyphae in soil or roots.

Structures in Roots- Hyphae - these are non-septate when young andramify within the cortex.- Vesicles - storage structures formed by many fungi.- Arbuscules - intricately branched haustoria in cortexcells.

.

Arbuscules

Glomeromycota (AM fungi)


Soil hyphae produce appressoriabetween epidermal root cells (arrows)to penetrate plant tissue.

(Bar = 100 um)

Hyphae at an entry point (E)penetrating cortex cells (arrows).

(Bar = 100 um)



Colony of a VAM fungus spreading fromthe entry point (E) by convoluted hyphae inthe inner cortex of an Erythroniumamericanum root.

(Bar = 100 um)

Mature arbuscule of Glomus mosseae withnumerous fine branch hyphae

(Bar = 10 um).



Vesicles (V) produced by a Glomus speciesin a leek root. This root also contains manyintercellular hyphae.

(Bar = 100 um)

Lobed vesicles of an Acaulospora species ina clover root.

(Bar = 100 um).


http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi Lab techniques

Spores can be separated from soil then sorted intomorphospecies (size, colour, etc). The image on theright shows how spores on a piece of filter papercan be used to start a "pot culture" usingpasteurised soil in which a host plant will be grown.---> fungal/plant specificity?---> effect on plant growth?---> effect on disease resistance---> etc.


Research in John Klironomos lab at U. Guelph and others has shown that:

- the effects of different species of arbuscular mycorrhizal fungi on plant growth varies withthe plant species considered, ranging from positive to neutral and sometimes negative growtheffects.

- arbuscular mycorrhizal fungi can influence the reproductive success of individual plantspecies, for example through indirect positive effects on pollinator visitation rates.

- AM fungi can have strong impacts on the composition and function of plant communities.

Applications- ecosystem restoration- control of invasive species?

http://www.uoguelph.ca/~jnklab/Research.htm


- three families and six genera;.

Gigasporaceae : Gigaspora and Scutellospora- form only arbuscules (no vesicles) in roots.

Acaulosporaceae: Acaulospora and Entrophospora- produce both vesicles and arbuscules in roots- produce "chlamydospores" in the soil- spores embedded in a swollen, sac-like structure-- Aculospora the spore forms laterally on the hyphae-- Entrophospora spore develops ‘within the neck’ of the hyphae

Glomaceae: Glomus and Sclerocystis- produce both vesicles and arbuscules in roots- chlamydospores are borne apically.

Spore of Glomus clarum

Spore of Acaulospora sp.

Pics from http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi


http://www.berkeley.edu/news/media/releases/2000/09/14_funghi.html

Light microscope pictureof a fossil fungal sporewith attached hypha fromthe Ordovician, 460million years ago.(c)Science MagazineCREDIT: DirkRedecker/UC Berkeley

Fossils from a Wisconsin roadcut show clearly thatfungi and green plants moved from water onto land atabout the same time, bolstering the theory that fungihelped plants successfully invade the land.

This particular fossil shows no evidence of associationwith plants, however other Devonian fossils (400million years ago) have been shown to containstructures indicative of arbuscular mycorrhizae.

http://mycorrhiza.ag.utk.edu/muthukumar7.htm

Glomusgeosporumspore

Fungal benefits- carbohydrates (= photosynthetic products) ==> converted to trehalose, mannitol, glycogen which arenecessary cofactor for spore germination.

Plant benefits- hyphae extend into the soil away from roots---> increase the potential for water absorption---> increase the potential for phosphorus uptake- currently debated to what extent, if any, fungi increase nitrogen uptake by host plant- endomycorrhizal associations may contribute to the resistance to certain root pathogens including variousfungi and nematodes by production of antibiotic substances

Two major types : AM vs. ECTO

- AM penetrates cortex cells ; ECTO do not

- ca.130 AM species for 300,000 plant species- > 5000 ECTO species for 2000 plant species

- ECTO: mostly trees- AM: woody & herbaceous plants

Mycorrhizal symbiosis


From Kendrick


From Kendrick

The Hartig netand mantle aretypical ofectomycorrhiza

Mycorrhizal symbiosis : Ectomycorrhiza

Pics from http://mycorrhiza.ag.utk.edu/mrecent.htm

Lactarius deliciosus on Pinus pinaster root tips

Tuber puberulum on Picea abies root tips

ThelephoroidectomycorrhizaOn Douglar fir

double colonizationby Tomentellasublilicina andThelephoroid#2 onBishop pine

unknownboletoid funguson bishop pine

http://plantbio.berkeley.edu/~bruns/


(A) penetration of hyphae between the cells of the rootcortex to form a characteristic Hartig net

(B) establishment of a mantle of hyphaearound the outside of the root (the brownlayer in the picture below);

(C) extension of hyphae from themantle into the surrounding soil

From Kendrick


Basidiomycotina euagarics Amanita Hygrophorus Tricholoma Cortinarius Inocybe bolete clade about 15 traditional bolete genera, including Boletus, Suillus, Leccinum etc. Scleroderma

Russuloid clade Russula, Lactarius Thelephoroid clade Thelephora, Tomentella

Cantharelloid clade Cantharellus

...

Ascomycotina Pezizales Pezizaceae (1 genus) Balsamiaceae (3) Otideaceae (1) Helvellaceae (1) Pyronemataceae (3) Terfeziaceae (4) Tuberaceae (2)

Elaphomyces

Taxonomic Distribution of Ectomycorrhizal (EM) Fungi About 90 genera and 5,000 species

Major taxa

Adapted from Kendrick

Other morpho-types than AM and EM exist, but are less widespread.For instance:

- orchid mycorrhizas;

- ericaceous mycorrhizas (mostly Ericales species)--- ericoid mycorrhizes;--- arbutoid mycorrhizas--- monotropoid mycorrhizas

Mycorrhizal associations: Non AM or ECTO types

Mycorrhizal associations

From Kendrick

The fungus enters cells of theroot cortex ands develops coilsor pelotons which eventuallyswell, degenerate and areabsorbed by the plant cell.

Orchid mycorrhizas

- Orchid seeds need a fungus to germinate--- plant depends on the fungus until chlorophyll-bearing leafdevelop (can take 1-2 years)

- commonly, these fungi are basidiomycetous anamorphs of thegenus Rhizoctonia--- holomorphs mostly in genera Thanatephorus, Corticium, andCeratobasidium--- Sebacina and Tulasnella species also commonly found.

Note: We can now use molecular identification.


Orchid mycorrhizas

Different possible outcomes of seedling colonization by a fungus:

(1) the seed becomes colonized by an appropriate fungus and thrives;(2) the fungal infection takes over, and kills the seedling;(3) the fungal invasion fails, the fungus is eliminated, and the seedling stops growing.

==> it does not appears to be a ‘true’ mutualistic symbiosis

Further specialization / dependence: achlorophyllous orchids, e.g., in genus Corallorizha-- other (ecto-!) fungi, e.g. Russula, Sebacina, etc…--gain for the fungus? Is the plant “cheating” ?

Arbutoid / Ericoid mycorrhizas

- intermediate between ecto- and endo-mycorrhizas:---- sheathing fungal mantle and typical ecto- branching;---- the fungus penetrates the cortical cells and fills them withdensely coiled hyphae (not arbuscules as in VAM)- Arbutoid type: Hartignet present- Ericoid type: does not produce a typical Hartig net

- characteristics ofEricales (rhododendrons, blueberrys, etc.)--- but can also (more rarely) be formed in other plant families,e.g., Fagaceae.- predominant in low pH soils and high altitudes and latitudes(Heath soils, tundra)- tend to be present in pioneer species.- apparently transfer nitrogen, but not phosphorus, to the host.

Some fungi can form normal ectomycorrhizas with sometrees and ericoid mycorrhizas with members of theEricaceae===> “plant signal”

Some fungi are restricted to Ericaceae and only form ericoidmycorrhizas.


From KendrickEricoid type

coiled hyphae(intracellular)

sheathing fungal mantle

See http://botit.botany.wisc.edu/courses/mpp/EricadMyco.html for more detailed info

Ericoid type

Monotropoid mycorrhizas

- known only with the achlorophyllous plantMonotropa (‘Indian pipe’)===> the plant (achlorophyllous) cannot providecarbohydrates to a fungal mycorrhizal partner…so what? “cheating” !

- the fungus produces a Hartig net and ahaustorium-like peg into root cell.

- Fungi involved: Tricholoma, Russula, Boletus;all typical ecto-

- tri-ways relationship--- it has been shown that the fungus also has anormal mycorrhizal relationship with aneighboring plant.


haustorium-like peg

Hartig net

From Kendrick

Evolution of ericaceous mycorrhizas in the Ericales

http://botit.botany.wisc.edu/courses/mpp/EricadMyco.html

arbutoid mycorrhizas

monotropoid mycorrhizas

ericoid mycorrhizes;

Unknown status?

Recent studies:Bidartondo, M. I.& Bruns, T. D. 2002. Fine-level mycorrhizal specificity in the Monotropoideae(Ericaceae): specificity for fungal species groups. Molecular Ecology 11(3): 557-569.M. I. Bidartondo and T. D. Bruns. 2001. Extreme specificity in epiparasitic Monotropoideae (Ericaceae):widespread phylogenetic and geographical structure. Molecular Ecology 10(9): 2285 - 2295.

eeb331-08 l17 glomero - university of...

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