Chapter 31 FUNGI (Part 1) Introduction, Ecological Impacts and Phylogenetic Relationships Wesley Jensen, Andrew Kam, Frank Zhang, Jeff Zhang

Introduction Fungi are mostly eukaryotic, and multicellular. Fungi are mostly eukaryotic, and multicellular. Fungi are unique organisms that differ from other eukaryotes in nutritional mode, structural organization, growth, and reproduction. Fungi are unique organisms that differ from other eukaryotes in nutritional mode, structural organization, growth, and reproduction. Fungi and Animals rose from the same ancestor. Fungi and Animals rose from the same ancestor.

Absorptive Nutrition Fungi acquire their nutrients by absorptive nutrition. Fungi acquire their nutrients by absorptive nutrition. Small organic molecules are absorbed from surrounding medium. Small organic molecules are absorbed from surrounding medium. Fungi digest food outside its body by secreting powerful hydrolytic enzymes into the food. Fungi digest food outside its body by secreting powerful hydrolytic enzymes into the food.

Absorptive Nutrition cont. The absorptive mode of nutrition specializes fungi into three types: The absorptive mode of nutrition specializes fungi into three types: Saprobic (decomposers): absorb nutrients from nonliving organisms. Saprobic (decomposers): absorb nutrients from nonliving organisms. Parasitic: Absorb nutrients from cells of living hosts. Some are pathogenic. Parasitic: Absorb nutrients from cells of living hosts. Some are pathogenic. Mutualistic: Absorb nutrients from host, yet reciprocate with functions that aid partners. Mutualistic: Absorb nutrients from host, yet reciprocate with functions that aid partners. (aid with uptake of minerals from soil) (aid with uptake of minerals from soil)

Fungi Growth Bodies of fungi are constructed of units called hyphae. Bodies of fungi are constructed of units called hyphae. Hyphae: minute threads composed of tubular walls surrounding plasma membranes and cytoplasm. Hyphae: minute threads composed of tubular walls surrounding plasma membranes and cytoplasm. Hyphae form a network called mycelium, which is the “feeding” network of the fungus. Hyphae form a network called mycelium, which is the “feeding” network of the fungus.

Fungi Growth cont. Most fungi are multi-cellular with hyphae divided into cells by cross-walls (septa). Most fungi are multi-cellular with hyphae divided into cells by cross-walls (septa). The septa have pores large enough to allow ribosomes, mitochondria, and nuclei to flow from cell to cell. The septa have pores large enough to allow ribosomes, mitochondria, and nuclei to flow from cell to cell. The hyphae are built from chitin (polypeptide similar to chitin found in external skeletons of insects) The hyphae are built from chitin (polypeptide similar to chitin found in external skeletons of insects)

Fungi Growth cont. Some fungi are aseptate, meaning their hyphae are not divided into walls. Some fungi are aseptate, meaning their hyphae are not divided into walls. They are known as coenocytic fungi. They are known as coenocytic fungi. Instead, they consist of a continuous cytoplasmic mass with hundreds or thousands of nuclei. Instead, they consist of a continuous cytoplasmic mass with hundreds or thousands of nuclei. Fungi usually have modified hyphae called haustoria which penetrate tissues of a host cell. Fungi usually have modified hyphae called haustoria which penetrate tissues of a host cell.

Fungal Reproduction (Asexual) They reproduce by releasing spores which are produced from specialized hyphal structures. They reproduce by releasing spores which are produced from specialized hyphal structures. Spores are created asexually, and are carried by wind or water. Spores are created asexually, and are carried by wind or water. They germinate if they are in a moist area. They germinate if they are in a moist area.

Fungal Reproduction (Sexual) Sex is a contingency mode of reproduction that occurs when there has been a change in the environment. Sex is a contingency mode of reproduction that occurs when there has been a change in the environment. Sexual reproduction results in greater genetic diversity among offspring. Sexual reproduction results in greater genetic diversity among offspring.

Fungal Sex Cycle Syngamy is the sexual union of cells that form two individuals. Syngamy is the sexual union of cells that form two individuals. There are two stages: There are two stages: Plasmogamy: Fusion of Cytoplasm Plasmogamy: Fusion of Cytoplasm Karyogamy: Fusion of nuclei. Karyogamy: Fusion of nuclei.

Plasmogamy In plasmogamy, the nuclei from each parent cell pair up but do not fuse, this forms a dikaryon (two nuclei) In plasmogamy, the nuclei from each parent cell pair up but do not fuse, this forms a dikaryon (two nuclei) Instead they coexist, providing advantages in the cell’s life. Instead they coexist, providing advantages in the cell’s life. One haploid genome compensates for harmful mutations in the other nucleus. One haploid genome compensates for harmful mutations in the other nucleus.

Karyogamy In karyogamy, the nuclei fuse, forming a diploid cell that undergoes immediate meiosis. In karyogamy, the nuclei fuse, forming a diploid cell that undergoes immediate meiosis.

Ecosystems Depend on Fungi as Decomposers and Symbionts Breakdown of wood, which makes nutrients available to living organism, became a dominant group of organisms about 250 million years ago Breakdown of wood, which makes nutrients available to living organism, became a dominant group of organisms about 250 million years ago Without fungi and bacteria, plants and animals would starve because elements taken from soil wouldn’t be returned Without fungi and bacteria, plants and animals would starve because elements taken from soil wouldn’t be returned

Continued Fungi’s invasive hyphae enter the tissues and cells of dead organic matter and hydrolyze polymers. Fungi’s invasive hyphae enter the tissues and cells of dead organic matter and hydrolyze polymers. Fungi can decompose anything from fruits/dung/forest litter to shower curtains and wooden boats. Fungi can decompose anything from fruits/dung/forest litter to shower curtains and wooden boats. We lose 10% to 50% of the world’s fruit harvest due to fungal attack. We lose 10% to 50% of the world’s fruit harvest due to fungal attack. Ethylene, a plant hormone that causes fruit to ripen also stimulates fungal spores on the fruit surface to germinate, causing the invasion of the fungi. Ethylene, a plant hormone that causes fruit to ripen also stimulates fungal spores on the fruit surface to germinate, causing the invasion of the fungi.

Some Fungi are Pathogens Plant diseases caused by fungi: Plant diseases caused by fungi: Ascomycete that causes Dutch elm disease has drastically changed the landscape of NE United States Ascomycete that causes Dutch elm disease has drastically changed the landscape of NE United States Aspergillus which is a species of mold which could contaminate improperly stored grain secretes aflatoxins which is a carcinogenic Aspergillus which is a species of mold which could contaminate improperly stored grain secretes aflatoxins which is a carcinogenic Ergots, caused by one type of ascomycete, that are ground with rye could cause humans to have hallucinations, temporary insanity, nervous spasms, gangrene Ergots, caused by one type of ascomycete, that are ground with rye could cause humans to have hallucinations, temporary insanity, nervous spasms, gangrene

Phylogenetic Relationships of Fungi Fungal ancestors were aquatic flagellated organisms. Fungal ancestors were aquatic flagellated organisms. Flagellated cells were lost as they became adapted for life on land. Flagellated cells were lost as they became adapted for life on land. The differences between the Zygomycota, Ascomycota, and Basidiomycota are focused on their solutions to reproducing and dispersing on land. The differences between the Zygomycota, Ascomycota, and Basidiomycota are focused on their solutions to reproducing and dispersing on land. Comparisons of RNA show that fungi are more closely related to animals than to plants. Comparisons of RNA show that fungi are more closely related to animals than to plants.

Many Animals, including humans, eat fungi A variety of mushrooms are consumed in various cultures. A variety of mushrooms are consumed in various cultures. Only an expert can determine safe to consume mushrooms. Only an expert can determine safe to consume mushrooms. There is no simple rule to determine poisonous and nonpoisonous. There is no simple rule to determine poisonous and nonpoisonous. Truffles are the most commonly consumed mushroom. Truffles are the most commonly consumed mushroom.