Chaetomium endophytes: a repository of pharmacologically ...
Symbioses: (including mycorrhizae, N- fixing, endophytes)
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Transcript of Symbioses: (including mycorrhizae, N- fixing, endophytes)
Questions
• Discussions: – Tatiana: posting paper and questions for this week– Maria M: will be picking a paper to post for next
week
• Paper due in 1 week• Any questions?
Symbioses
• Who are they and what do they do?– Mycorrhizal fungi (http://mycorrhizas.info),
Endophytes, and Nitrogen-fixing bacteria
Mycorrhizae
• Define: Root-fungi association that is not pathogenic– A fungus that invades the root (cortex)– Roots typically have few to no root hairs, but
fungus has better uptake• Mycelia are small in diameter• Excretes organic acids
• Two main types: EM and VAM
Distribution• Most plants have mycorrhizal associations– VAM is more common and ancestral ~80% of
species• First records from 400 mya with early bryophytes• Fossils show association since plants first colonized
land
– EM found in ~10% of species in specific clades (e.g., Pinaceae, Fagales, Malvales, Cyperaceae, Caryophyllales)
Distribution• Most plants have mycorrhizal associations
(with other types evolving during Cretaceous)– Ericaceae (complex with VAM ancestral)– Orchid (single lineage)– Myco-heterotrophic plants with Exploitative:
primitive, eudicots (e.g., Ericaceae) and monocots (e.g., Orchidaceae)
– Nonmycorrhizal found in disturbed habitats with extreme conditions
Mycorrhizae
• Fungus: – Accesses water and minerals from the soil and
decaying material and provides them in a form the plants can use (especially P)
– Protects plants against pathogenic fungi
• Plant: – Provides sugars, amino acids, and other organic
materials
• Dependent on coordinated growth of root and hyphae
EM: Cortical and Epidermal• Ectomycorrhizal (EM): Basidiomycota,
Ascomycota, Zygomycota; Gymnosperm & Angiosperm– Covers the root tip with a dense hyphal mantel – Hartig net: Hyphae invades intercellular spaces– Roots are short, branched and look swollen– Root hairs growth is suppressed
VAM: A number of types
• Endomycorrhizal/Vesicular arbuscular mycorrhizal (VAM): Glomeromycota; Most plants– The mantle is less obvious – Fungal hyphae invade intracellular spaces. They
have arubscules (exchange) and vesicles (storage)
Tripartite: A fungus, an underground orchid (Rhizanthella gardneri), and a Melaleuca (Melaleuca uncinata)
Endophytes
• Distribution: – Most plants• Especially studied in Poaceae• Found in shoots, roots and rhizomes
– Fungi: differ in type of host, where they colonize, how they are transmitted, and fitness benefits to plant• Clavicipitaceous (class 1); grasses• Nonclavicipitaceous (class 1, 2, and 3); vascular and
non vascular plants
Endophytes
• Poorly understood, – Protect plants against pathogens, growth enhancers,
and tolerance of drought, pH, salinity, and temperature
• Transmitted vertically (parent to offspring) via fungal hyphae or horizontally (among unrelated individuals) via spores
• Live completely within host (spores produced on host senescence)
• Important endophytic chemical?
Nitrogen-fixing bacteria
• Where is bulk of N? • Distribution:– Plants: Found in 4 orders in the subclade of the
rosids I (Fabales, Rosales, Cucurbitales, Fagales)– Bacteria: Frankia and Rhizobium are often
involved– Also ferns, cycads, and Gunnera with
cyanobacteria associates
Nitrogen-fixing bacteria
• Plant roots form nodules where bacteria are located
• N2 + 6 H -> 2 NH3 (anaerobic)
Question
• Can undestory green plants obtain some of their carbon from overstory green plants via fungal networks? – Orchids: Shown already that mixotrophy can
evolve near mycoheterotrophic taxa– Ericaceae: Can this model be used to predict
mixotrophy taxa?
Question
• Can undestory green plant obtain some of their carbon from overstory green plants via fungal networks? – Orchids: Shown already that mixotrophy can
evolve from mycoheterotrophic taxa– Ericaceae: Can this model be used to predict
mixotrophy evolution?• Used δ13C to show that Pyroleae have C signatures
suggesting some C acquisition from fungi• Suggest 2 adaptations: vernal photosynthesis & fungal
C exploitation