Fungi 1

FUNGI

Chapter 29: Diversification of Fungi

• Key lineages

• Ecological importance

• Link: FUNGI

Taxonomic Classification

• Domains of Life:

  • Domain Bacteria

  • Domain Archaea

  • Domain Eukarya

    • Kingdom Fungi

    • Kingdom Plantae

    • Kingdom Animalia

    • Kingdom Protista

• Common Ancestor: Ancestral eukaryote

Key Eukaryotic Groups

• Excavates:

  • Diplomonds

  • Euglenoids

  • Dinoflagellates

  • Apicomplexans

  • Ciliates

• Chromalveolates:

  • Alveolates

  • Water molds

  • Diatoms

  • Stramenopiles

    • Brown algae

    • Golden algae

• Rhizarians:

  • Forams

  • Actinopods

• Archaeplastids:

  • Red algae

  • Green algae

  • Land plants

• Unikonts:

  • Amoebas

  • Plasmodial slime molds

  • Cellular slime molds

  • Opisthokonts

    • Fungi

    • Choanoflagellates

    • Animals

Introduction to Fungi

• Characteristics:

  • Eukaryotic organisms

  • Can be unicellular or multicellular

  • Some species specialize in absorbing nutrients from living organisms

  • Many species are mutualists—benefit their hosts

Diversity and Distribution

• Species Count: Approx. 100,000 described species

• Fungi are widespread

• Shared unifying traits:

  • Eukaryotic heterotrophs

  • External digestion via enzymes to break down complex molecules

  • Cell walls made of chitin

Importance to Ecosystems

• Role as Decomposers:

  • Recycle nutrients by breaking down organic material

  • Release nutrients from dead plants and animals

• Some species transfer nutrients to living plants

• Major impact on productivity and biodiversity

Other Significance

• Pathogenic Fungi:

  • Approx. 30% of fungal species are parasitic or pathogenic, primarily affecting plants

  • Fungi can cause diseases in humans, livestock, and crop plants

  • Annual loss of 10-50% of the world's fruit harvest due to fungi

  • Some fungi that attack crops are also toxic to humans

Human Impact

• Diseases Caused by Fungi:

  • About 300 species of parasitic fungi cause human diseases, such as:

    • Athlete’s foot

    • Ringworm

    • Pneumonia

  • Incidence of fungal diseases is relatively low compared to other organisms

Beneficial Interactions

• Fungi as Sources of Antibiotics:

  • E.g., Penicillin derived from fungi.

• Edible mushrooms are consumed in many cultures.

• Yeasts used in various food and beverage production:

  • Bread

  • Cheese

  • Soy sauce

  • Tofu

  • Beer

  • Wine

• Fungi also ferment cacao seeds for chocolate production.

• Fungal enzymes improve the quality of juices, candies, and meats.

Symbiotic Relationships

• Historical Significance:

  • The first plants in the fossil record are associated with fungal fossils,

  • Early evolution of land plants may have involved nutrient absorption facilitated by fungi.

• 90% of contemporary land plants exist in physical contact with fungi.

• Mycorrhizae:

  • Supply water, nitrogen, and phosphorus to host plants.

Mycorrhizal Fungi Benefits

• Provide essential nutrients (water, phosphorus, nitrogen) for plants

• In exchange, plants provide carbohydrates to fungi.

• Increased plant fitness observed with mycorrhizal partners.

Experimentation

• Mycorrhizal Networks:

  • Extensive networks of mycorrhizal fungi observed in soil.

  • Experimental results show enhanced plant growth with mycorrhizal fungi present compared to absence.

Types of Symbiotic Relationships

• Mutualism:

  • Both organisms benefit (e.g., bees and flowers).

• Commensalism:

  • One organism benefits without affecting the other (e.g., barnacles on whales).

• Parasitism:

  • One organism benefits at the expense of another (e.g., ticks feeding on cats).

Endophytes

• Definition:

  • Live within the tissues of specific plants.

  • Help protect the plant against herbivores.

  • Produce toxic compounds.

  • Enhance drought tolerance of host plants.

  • Absorb sugars from the plant in return.

Research Findings on Endophytes

• Experimental results demonstrate how endophytes contribute to plant health by reducing leaf mortality and damage.

• Presence of endophytes and pathogens studied with respect to leaf mortality percentage and leaf area damaged percentage:

  • Results show reduced damage when endophytes are present.

Mycorrhizal Interactions

• Two Types of Plant–Mycorrhizal Associations:

  1. Ectomycorrhizal fungi (EMF):

  • Form dense networks covering plant roots without entering root cells.

  1. Arbuscular mycorrhizal fungi (AMF):

  • Grow into the cells of root tissue.

  • Also known as endomycorrhizal fungi.

• EMF Functionality:

  • Hyphae penetrate decaying materials releasing peptidases, which cleave proteins into amino acids for plant absorption.

  • Provide phosphate ions to the plant in return for sugars.

AMF Structure and Function

• Hyphae adaptation increases surface area for molecular exchange

• Pipeline extends from plant roots into the surrounding soil, promoting nutrient exchange.

Role of Fungi in Animal Digestion

• Some insects harbor single-celled fungi in their guts that assist in digesting plant material.

• These fungi enable animals like cows to effectively break down plant material in their digestive systems.

• Many ant species cultivate fungi in "farms" for nutritional benefits.