Lecture 11

Fungi: Recyclers, Pathogens, Parasites, and Plant

Partners Dr. Angelika Stollewerk

Chapter 30

Fungi

Aims:

• To understand the basic biology of fungi

• To show the diversity in the kingdom

of fungi

• To introduce fungal associations

Fungi

Aims:

• To understand the basic biology of fungi

• To show the diversity in the kingdom of fungi

• To introduce fungal associations

These lecture aims form part of the knowledge required for learning outcome 2:

Describe basic organism structure and diversity (LOC2).

Fungi

Essential reading

•pages 650-663

Recommended reading

Pages 74-75: 4.3 What are the characteristics of eukaryotic cells (This will be covered in depth in SEF032 Molecules to cells, but it is useful background here)

30 Fungi: Recyclers, Pathogens, Parasites, and Plant Partners

• 30.1 How Do Fungi Thrive in Virtually Every Environment?

• 30.2 How Are Fungi Beneficial to Other Organisms?

• 30.3 How Do Fungal Life Cycles Differ from One Another?

Fungi and animals are descended from a common ancestor: A unicellular eukaryote with a flagellum

Figure 30.1 Fungi in Evolutionary Context

Synapomorphies that distinguish the fungi:• Absorptive heterotrophy

• Chitin in cell walls

Fungi and animals are descended from a common ancestor: A unicellular eukaryote with a flagellum

30.1 How Do Fungi Thrive in Virtually Every Environment?

Absorptive nutrition

• Saprobes: absorb nutrients from dead organic matter

• Parasites: absorb nutrients from living hosts

• Mutualists: both partners benefit

Figure 30.2 Phylogeny of the Fungi

Bread mold

Mush-rooms

30.1 How Do Fungi Thrive in Virtually Every Environment?

Yeasts: Unicellular members of the zygomycetes, ascomycetes, and basidiomycetes.

Budding: mitosis followed by asymmetrical cell division.

30.1 How Do Fungi Thrive in Virtually Every Environment?

Multicellular fungi:

• Body is a mycelium—composed of tubular filaments called hyphae.

• Hyphae cell walls have chitin.

• Some hyphae have incomplete cross walls or septa, and are called septate.

• Hyphae without septa are called coenocytic.

Figure 30.4 Most Hyphae Are Incompletely Divided into Separate Cells

mycelium

Septate hypha

Septum

CoenocyticHypha(No septa)

30.1 How Do Fungi Thrive in Virtually Every Environment?

Rhizoids: modified hyphae for anchoring.

Hyphae can grow 1 kilometer a day!

Hyphae may reorganize to form a fruiting body such as a mushroom.

A fungal mycelium has a large surface area-to-volume ratio.

Good for absorptive nutrition;

But water loss also high—fungi are mostly in moist environments.

30.1 How Do Fungi Thrive in Virtually Every Environment?

Many fungi can tolerate hypertonic environments.

Many fungi tolerate temperature extremes.

Fungi exploit many nutrient sources:

Saprobes get their energy, carbon, and nitrogen directly from dead organic matter.

30.1 How Do Fungi Thrive in Virtually Every Environment?

Fungi exploit many nutrient sources:

Parasites:

Facultative

Obligate

Hyphae can invade plant tissues, and may produce haustoria, projections that press into cells without breaking through the plasma membranes.

Figure 30.5 Attacks on a Leaf

Haustorium

hyphae

Fungal spore

30.1 How Do Fungi Thrive in Virtually Every Environment?

Some parasitic fungi are pathogens.

Fungi are the most important pathogens in plants.

Predatory fungi trap microscopic organisms.

Figure 30.7 Spores Galore

Fungi reproduce rapidly when nutrient supplies dwindle.

30.2 How Are Fungi Beneficial to Other Organisms?

Saprobic fungi (along with bacteria) are the major decomposers on Earth.

• Earth’s “rubbish disposal”

• Soil formation

• Recycling nutrient elements

Mould growth and decomposition on bread and fruit

30.2 How Are Fungi Beneficial to Other Organisms?

Symbiotic (close, permanent association), mutualistic (both partners benefit) relationships:

Lichens

Mycorrhizae

30.2 How Are Fungi Beneficial to Other Organisms?

Lichens: fungus + photosynthetic organism

• Fungi—mostly ascomycetes

• Photosynthetic partner—cyanobacterium or alga, or both.

• Species are named for fungal component.

30.2 How Are Fungi Beneficial to Other Organisms?

Lichens:

• Can survive harshest environments on Earth.

• Very sensitive to toxic compounds—good indicators of air pollution.

Figure 30.9 Lichen Anatomy

30.2 How Are Fungi Beneficial to Other Organisms?

Mycorrhizae: Association between plant roots and fungal hyphae.

Ectomycorrhizae—fungus wraps around the plant roots.

Web of hyphae penetrates soil around roots, increase surface area for water and mineral absorption.

30.2 How Are Fungi Beneficial to Other Organisms?

Mycorrhizae: Association between plant roots and fungal hyphae.

Arbuscular mycorrhizae: hyphae enter root and penetrate cell walls, but not plasma membrane.

Figure 30.10 Mycorrhizal Associations

30.2 How Are Fungi Beneficial to Other Organisms?

Mycorrhizae are essential to almost all vascular plants to increase water and mineral uptake.

The fungus gets sugars and proteins from the plant.

Fungus may also protect plant against disease organisms.

30.2 How Are Fungi Beneficial to Other Organisms?

Evolution of mycorrhizal associations may have been an important step for plants to colonize land.

Plant roots secrete a chemical signal that enables the fungi to find them.

30.2 How Are Fungi Beneficial to Other Organisms?

Endophytic fungi: living in aboveground parts of plants.

Produce alkaloids, chemicals that help give resistance to pathogens and herbivores, and stresses such as drought.

30.2 How Are Fungi Beneficial to Other Organisms?

Some leaf-cutter ants “farm” fungi:

Fungus grows on leaf bits and produces special fruiting bodies—gongylidia. Ants feed on the gongylidia. The “gardens” consist of one single clone of fungus. Other fungi are killed by substances in the ant faeces.

Figure 30.11 Keeping Fungal Interlopers Away (Part 1)

Figure 30.11 Keeping Fungal Interlopers Away (Part 2)

30.3 How Do Fungal Life Cycles Differ from One Another?

Asexual Reproduction in Fungi:

• Production of haploid spore in sporangia.

• Production of naked spores called conidia.

• Cell division by unicellular fungi—fission or budding.

• Breakage of the mycelium.

30.3 How Do Fungal Life Cycles Differ from One Another?

Sexual reproduction:

Mating types are genetically different, but not physically different. Individuals of the same type cannot mate.

30.3 How Do Fungal Life Cycles Differ from One Another?

Sexual reproduction:

In a haplontic life cycle, the zygote is the only diploid stage.

Some groups have a unique n + n stage called a dikaryon.

Some groups have alternation of generations.

Figure 30.12 Asexual and Sexual Reproduction in a Fungal Life Cycle

Fusion of cytoplasm

Fusion ofnuclei

Generalisedfungallife cycle

30.3 How Do Fungal Life Cycles Differ from One Another?

Alternation of Generations: Chytrids

Flagellated male and female gametes.

Multicellular haploid stage may be a “filter” for harmful mutations.

Multicellular diploid stage includes a structure that can withstand freezing and drying.

Figure 30.13 Sexual Life Cycles Vary among Different Groups of Fungi (A) Chytrids

Multicelluarhaploid chytrid

female

malegametangium

Fertilization

Multicellulardiploidchytrid

SporangiumHaploidzoospores

30.3 How Do Fungal Life Cycles Differ from One Another?

All other fungal groups do not have flagellated gametes.

Plasomogamy: cytoplasms of individuals of different mating types fuse.

Karyogamy: the nuclei fuse to form a diploid zygote.

Liquid water is not required for fertilization.

30.3 How Do Fungal Life Cycles Differ from One Another?

Many species lack a sexual stage—now classified using DNA sequencing.

Deuteromycetes or “Imperfect Fungi”—polyphyletic group of species that have not yet been placed in any existing group.

25,000 species

Table 30.1 A Classification of the Fungi

Figure 30.17 Two Cup Fungi

Amanita muscaria

Fungi

Check out

30.1 Recap, page 654

30.2 Recap, page 659

30.3 Recap, page 663

30.1 Chapter summary, page 668 see WEB/CD Activity 30.1

30.2 Chapter summary, page 668

30.3 Chapter summary, page 668 see WEB/CD Activities 30.1 and 30.2

Self Quiz

Pages 668-669: Chapter 30 questions 1-4 and 10

For Discussion

Page 669: Chapter 30 questions 1, 2, 4, 5, 6, 7 and 8

Key terms:

absorptive heterotroph, absorptive nutrition, Ascomycetes (Ascomycota), ascospores, ascus, basidium, Basidiomycetes (Basidomycota), biotin, chitin, Chytrids (Chytridiomycota), coenotypic, conidia, cyanobacteria, decomposer, dikaryon, ectomycorrhizae, endomycorrhizae, facultative parasite, haustoria, heterokaryon, hypertonic, hypha (pl. hyphae), karyogamy, lichen, mutualisitic, mycelium (pl. mycelia), mycorrhizae, nematode, pathogen, plasmogamy, rhizoid, saprobes, saprotophs, septate, septum (pl. septa), soredium (pl. soredia), sporangium (pl. sporangia), spores, symbiotic, thallus, thiamin, yeasts, Zygomycetes (Zygomycota), zygote

Fungi