Symbioses: (including mycorrhizae, N-fixing, endophytes)

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

FernsGymnosperms

Angiosperms

Fungi

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

EM: Monotropoid

• Basidiomycota; Myco-heterotrophic ericoid plants

EM: Arubtoid

• Basidiomycota; Ericaceae

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)

Orchid

• Basidiomycota; Orchidaceae (root, stem, exploitative - myco-heterotrophic)

Ericoid

• Ascomycota; Ericaceae

But…

• Fungi can be cheaters (pathogenic, parasitic, or saprophytic)

Myco-heterotrophic

• And so can plants– Orchidaceae (germination!)– Ericaceae

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)

Evolution of mixotrophy

Tedersoo

Selosse

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?

Evolution of mixotrophy

FernsGymnosperms

Angiosperms

Evolution of mixotrophy

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