Lecture 3: Fungal symbioses with plants

Important symbioses

• prokaryotes: involved in N fixing, important for all life

• Fungi: involved in nitrogen extraction, and form colonies with cyanobacteria to form Lichens

Taxonomy

The theory and practice of grouping individuals into species, arranging species into larger groups, and giving these groups names, thus producing a classification.

Systematics

The science of organismal diversity, establishing relationships between species.

Why base classification on evolution?

Knowing the identity of something is potentially informative of what it does, where it lives, as well as what it looks like.

The Linnaean hierarchy

Domain

Kingdom

Phylum

Class

Order

Family

Genus

Species

Dear Katy Perry came over for good spaghetti

Plural of genus

genera

Plural of phylum

Phyla

Derived trait

a new trait different from an ancestral trait is the derived trait

• looking at derived trait that species have in common

• ingoring all shared ancestral traits every species might have to help narrow it down

Monophyletic

the group contains

1. its own most recent common ancestor

2. all descendants of that common ancestor

• every taxon (names group) should be monophyletic

Paraphyletic

a group has its own most recent common ancestor

BUT not all of the descendants share the same common ancestor

Polyphyletic

a group that doesn't not have its own most recent common ancestor

all the descendants do not share that common ancestor

Synapomorphy

a derived trait shared by other taxonomic groups because of a common ancestor that helps it from other groups

• example: flowers differentiate angiosperms from gymnosperms

Symplesiomorphy

a trait shared by taxonomic groups because of a common ancestor that does not help differentiate it from other groups

Convergence

the independent evolution of similar trails (often because of similar selection pressure)

Homology

shared or similar trait because of shared ancestry (could be derived or ancestral)

Homoplasy

shared or similar trait because of convergence

Symbioses - photosynthesis

plants have chloroplasts because of symbioses with bacteria

• cyanobacteria are the likely ancestor of green chloroplasts

  • still exist, large organisms

Symbioses - nitrogen fixing

converting nitrogen in are to usable form costs a lot of energy

• 78% of atmosphere contains nitrogen that most of life cannot access

• only prokaryotes can fix it for it then to be used by other life

  • some fixing done by free living bacteria in the soil, or in cyanobacteria

  • other fixing

Phylum proteobacteria and leghemoglobin

Rhizobium in N2 fixing association (nodule) with legumes from family Fabaceae

• leghemoglobin in root nodules help protect the oxygen-sensitive nitrogenase enzymes from oxygen

• root nodules have evolved three times in Fabaceae, not all species in the family have them

Symbiosis - mycorrhizae

Myco = fungus

rhiza = roots

• usually mutualistic symbiosis between fungi and roots or other under ground organs of plants

• help with extraction of nutrients/water

• may help protect roots against parasites

*Term refers to association of structure, not to the fungus or plant

Types of Mycorrhizae

1. Arbuscular or end-

• intracellular

• Glomeromycota

2. ecto- (ECM)

• Extracelluar

• Basidyomycota and Ascomycota

Phylum Glomeromycota

form arbuscular mycorrhizal (endomycorrhizae) associations with most land plants (liverworts to agiosperms)

Phylum ascomycota

a few associate with roots of selected vascular plants to form ectomycorrhizae, this is the largest phylum

Phylum Basidiomycota

many species associate with the roots of selected vascular plants to form ectomycorrhizae

Which fungi form ectomycorrhizae

• phylum ascomycota

• phylum basidiomycota

which fungi form arbuscular mycorrhizae

Phylum Glomeromycota

endomycorrhizae

• another term for arbuscular mycorrhizae

  • almost all grasses form this

• formed by Glomeromycota in association with a great diversity of green plants, predominantly herbaceous, or tropical woody plants

  • fungal hyphae penetrate cell walls but not the plasmalemma of root cortex

  • within root cells, form shrubby arbuscules for nutrient transfer or sometimes oily vesicles for storage/survival

  • form spores in soil or dead roots - no fruiting bodies

  • particularly important in delivery of phosphorus

T/F: plant evolution depended on mycorrhizae

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• early plants lacked any roots, fungi may have provided access to water and nutrients

• mycorrhizae show up in fossil records up to 407 million years ago

Ectomycorrhizae

• formed by various groups of Basidiomycota (90% are in agaricomycetes)

• a few Ascomycota

  • in association with predominantly temperate woody plants

Hyphae do not (usually) penetrate cell walls of plant roots, but form a mantle over the root then a network of hyphae between cortex cells called Hartig net

• form large sexual fruiting bodies, above or below ground

Ecological significance of mycorrhizae

• many plants would not thrive in harsh conditions without them

  • mitigate drought, nutrient limitation, root pathogens

  • shown to impact composition of the plant community

  • many organisms feed on mycelium or fruiting bodies of mycorrhizal fungi