Chapter 32 - Fungi

Arbuscular mycorrhizal fungi (AMF) - AKA. ENDOmycorrhizal fungi

- found in glomeromycota - grow INTO the root cells of plants and contact the plasma membrane of the root cells directly - feature highly branched hyphae that increase surface area for absorption - do not form a tight sheath around root like EMF. Instead, they form a pipeline extending directly form the root cells into the soil - found in 80% of land plant species - found particularly in forests of TROPICAL HABITATS, but also in temperate forests too - nitrogen is readily available in tropical habitats - AMF aren't needed fro nitrogen - however, phosphorus is in short supply; MOST IMPORTANT FUNCTION OF AMF IS TO TRANSFER PHOSPHORUS FROM SOIL TO HOST PLANT - their cell walls contain a lot of glycoproteins called GLOMALIN. When AMF cells die, the glomalin enriched the organic content of the cell by helping to bind organic compounds

What are some economic impacts of fungi

- fungi can cause infections like athlete's foot, vaginitis, diaper rash etc - penicillin, the first antibiotic, is a type of non-lichen-former (ascomycete) - parasitic fungi known rusts, smuts, mildews, wilts, and blights infect crops like wheat, corn, barley, and other grains - saprophytic fungi rot fruits and veggies top - fungi can cause epidemics (eg. White nose disease in bats, infection of chestnut trees) - mushrooms (basidiomycota) are consumed by animals, including humans - yeasts are essential for producing wine, bread, soy sauce, tofu, cheese, beer, wine etc (yeast cells grow via fermentation, producing by-products like CO2)

In what ways is mycelia dynamic?

- its body shape constantly changes throughout its lifetime - it grows in the direction of food sources and moisture and dies back in areas where food is running out

What are the 3 major lineages that consists of large, multicellular eukaryotes that occupy terrestrial environments?

- land plants - animals - fungi

Characteristics of chytrids

- largely AQUATIC - only fungi that produce motile cells (swimming gametes and spores) that swim to new habitats via a flagellum - have enzymes that allow then to digest cellulose making them important decomposers of plant material in wet areas - decomposers, parasites, mutualists - they live in the guys of mammals like deer and cows, helping them to digest their food - only fungi to exhibit alternation of generations (switch between asexual and sexual reproduction)

What are some examples of mutualistic relationships between fungi and other non plant species?

- lichen: mutualistic partnership between ascomycota and a cyanobacterium or an alga - some ant species actively farm fungi inside their colonies (they fertilize and weed fungal gardens) to use the fungi for food

Why do fungi break down lignin?

- lignin itself is not a food source for fungi because lignin peroxidase digest uncontrollably; they cannot harness oxidation to produce ATP. - they just digest the lignin to get to the cellulose inside

Why are fungi essential fro farmers, foresters, and ranchers?

- mycorrhizal fungi are essential for facilitating the growth and efficiency of many plants;

Characteristics of basidiomycota (AKA club fungi)

- named for basidia, club-like/pedestal-like cells where meiosis and spore formation occur - saprophytic, mutualistic, and parasitic (some are EMF) - only organisms (along w a few soil dwelling bacteria) to produce lignin peroxidase and therefore, able to completely digest wood - include mushrooms, bracket fungi, and puffballs - formed from DIKARYOTIC mycelium - Important saprophytes - only fungi able to produce lignin peroxidase - asexual reproduction is common in basidiomycota - used as food, drugs

Characteristics of ascomycota (sac fungi) - lichen-formers

- over half of all known fungi belong to the ascomycota - two major groups of ascomycota: lichen-formers and non-lichen formers - lichen formers are formed when there is a symbiotic relationship between a fungus and Cyanobacteria or green alga - fungus provides protection while the cyanobacterium or alga provides food (some relationships are parasitic - fungus sometimes invades algal cells and kills them) - many lichens reproduce asexually via the production of small "mini-lichen" structures called soredia, that contain both symbionts - found in the Arctic and Antarctic tundra and boreal forests - major food of caribou - able to colonize bare rock surfaces. This is helpful because they break off mineral particles from the rocks, which initiate soil formation - used in perfume production

How do saprophytic fungi break down cellulose?

- secrete an enzyme called cellulases - unlike lignin peroxidase, cellulase facilitates highly organized and specific action (like ETC) that allows the cellulose to be broken down into glucose monomers that can be used for food

Why is it harder to treat fungal infections than bacterial infections in humans?

- since animals and fungi are more closely related than bacteria and animals, the former pair have more similar enzymes and cell structure + function, so drugs that are mean to kill the fungal cells are likely to damage the animal ones too

Characteristics of microsporidia

- single celled and PARASITIC - infect other cells via a polar tube (penetrates membrane of host cell) - dramatically reduced genome - lack functioning mitochondria - used to be thought of as protozoans or Protista - 8 species can infect humans

Characteristics of zygomycetes

- soil dwelling saprophytes - some parasitize other fungi, insects and spiders while others are predatory - eg. Bread mold and responsible for rotting fruits and veggies - usually engage in ASEXUAL REPRODUCTION (zygosporangia produce spores that are dispersed in the wind) - some are used in the production of medical steroids, organic acids, pigments, alcohols, and fermented foods

What is the most fundamental reproductive cell in fungi? Why?

- the spore - the dispersal stage in the fungal life cycle - produced during sexual and asexual reproduction - important because fungi produce them in such enormous quantities - when there is a food source, a mycelium will begin to form, the hyphae growing in the direction of the food - BUT, if there is no food, mycelia respond by making spores (dispersed by wind or animal feces)

What are the two mycorrhizal fungal types and how are they distinguished from each other?

- the two types are distinguished by the method of absorption, distinct morphologies, and geographic distribution 1. Ectomycorrhizal fungi (EMF) 2. Arbuscular mycorrhizal fungi (AMF) - glomeromycota

Why are fungi known as the master recyclers and traders in terrestrial ecosystems?

- they are master recyclers because they decompose dead plants and animals so that other organisms can reuse the nutrients within them - they are master traders because they form mutualistic relationships with plants: in exchange for sugars made by the plant, the fungi provide it with water and key nutriments like phosphorus and nitrogen

Ascomycota and basiomycetes are their own monophyletic groups, but they both also dikaryotic - what does this mean?

- they form a clade; the dikaryotic feature is a synapomorphy that groups them together as one larger monophyletic group

How do scientists explore the nature of plant-fungi symbioses experimentally?

- they use radioisotopes for tracers of different elements and analyze the transfer of these elements between plants and fungi - to test whether fungi obtain food from plants, researchers use radioactively labelled carbon dioxide to document the transfer of sugar to fungi - to test whether plants obtain nitrogen and phosphorus form fungi, scientists put these radioactively labelled elements in the soil and see whether they transfer from fungi to plant

Ectomycorrhizal fungi (EMF)

- usually species from basidiomycetes (and some ascomycetes) - found in temperate regions (alternate between hot and cold), usually on trees in boreal forests - hyphae form a DENSE NETWORK (OUTER SHEATH - hense, "ecto") that covers a plant's root tips - individual hyphae penetrate between outside layer root cells (but do not enter the cells) and also extend out into the soil - SECRETE enzymes called peptidases that cleave the peptide bonds between amino acids in dead tissue, allowing the hyphae to absorb the AAs and transport them to the spaces between root cells to be used by the plant - acquire phosphate and nitrogen ions that are bound to soil particles and transfer them to plant - known as the dominant nutrient gathering organ in most temperature forest ecosystems

What 2 features usually distinguish fungi as their own lineage of eukaryotes?

1. Filamentous, web-like body (mycelium) 2. Absorb nutrients

What are the two basic components of the carbon cycle on land and how do fungi speed it up?

1. Fixation of carbon by land plants (CO2 in the atmosphere is converted into compounds like cellulose, lignin, etc) 2. Release of CO2 from plants, animals, and fungi as the result of cellular respiration - fungi connect these two steps; fungi digest dead plant and animal tissue, unlocking the carbon compounds from within them, recycling them for further use by other organisms

What are the two distinct steps that fertilization occurs in?

1. Fusion of cells (plasmogamy) 2. Fusion of nuclei from the fused cells (karyogamy)

What adaptations that allow fungi (and a few bacterial species) to digest wood completely?

1. Large surface area of mycelium makes absorption efficient 2. Saprophytic fungi are able to grow toward the dead tissues that supply their food 3. Extracellular digestion (secretion of lignin peroxidase and cellulase)

What are the 4 types of fungal reproductive structures?

1. Swimming gametes (sexual reproduction) and spores (asexual reproduction) - in species that live in water or wet soils - have flagella (only motile cells known in fungi) - species that have swimming gametes are known as CHYTRIDS 2. Zygosporangia ("zygo" means to yoke together like oxen) - spore producing structures formed when haploid hyphae from two individuals meet and yoke together - species with these structures are known as ZYGOMYCETES 3. Basidia - specialized cells that look like little pedestals that form on the ends of BASIDIOMYCETE'S hyphae and produce spores and facilitate meiosis - found inside mushrooms, brackets, or puffballs 4. Asci - specialized SAC LIKE cells that form at the ends of ascomycetes hyphae where meiosis occurs and spores form - found inside cups, morels, and other ABOVE GROUND reproductive structures

What are the only two growth forms that occur among fungi?

1. Yeast (single-celled forms) 2. Mycelia (multicellular, filamentous structures) - fundamental to the absorptive mode of life - some species of fungus can adopt both forms

When it comes to making a living, land plants, animals, and fungi all differ radically in terms of how they make a living. Whereas plants make their own food and animals ingest/eat other organisms to sustain themselves, fungi...

ABSORB their nutrition from other organisms - dead or alive

What is a saprophyte?

An organism, especially a fungus or bacterium, that lives on and gets its nourishment from dead organisms or decaying organic material. Saprophytes recycle organic material in the soil, breaking it down into in simpler compounds that can be taken up by other organisms

Which of the following results would support Simard et al.'s (1997) hypothesis that individual fungi can move carbon from one plant to another? Hypothesis: Sugars made by one plant during photosynthesis can travel through a mycorrhizal fungus and be incorporated into the tissues of another plant. - birch uses Carbon-14, Douglas fuir uses carbon-13 (diagram on slide 61) a) Carbon-14 is found in the birch seedling's tissues and carbon-13 in the Douglas fir. b) Carbon-14 is found in the Douglas fir seedling's tissues and carbon-13 in the birch. c) Either carbon-13 or carbon-14 is found in the fungal tissues. d) Either carbon-13 or carbon-14 is found in the cedar seedling's tissues.

B); the only way for the trees to contain the type of carbon that they can't use is if the fungi transferred the carbon from an other plant.

Fungi (and a few species of bacteria) are the only organisms capable of FULLY decomposing _________ and __________. What is the significance of this?

Cellulose (plant cell walls) and lignin (wood). Without fungi, dead tree trunks and branches would pile up on Earth's surface, the nutrients within them unavailable to primary producers.

What is the only fungal species to exhibit alternation of generations (that is, produce gametes)?

Chytrids; it can exist as both a haploid individual (gamtophyte) and a diploid individual (sporophyte)

T or F: septa close off segments of hyphae completely.

F; septa contain gaps called pores that enable a wide variety of materials, even organelles, to flow from one compartment to the next - this ability for organelles to flow throughout the entire system of mycelia causes the fungal mycelium to be an INTERMEDIATE between a multicellular land plant and an enormous single felled organism

T or F: fungi produce sperms and eggs

F; the gametes that chytridiomycota produce are not different enough in size to be called sperm and egg - also, fungi do not have morphologically distinct males and females, just hyphae of different mating types

Conifer seedlings cannot grow, even in nutrient rich soils without...

Fungal mutualists; fungi play an important role in forest REGENERATION after replanting

What are mycorrhizal fungi? How are they different from endophytic fungi?

Fungi that form symbiotic (together-living) relationships with land plants by forming an extensive network in the soil that attaches to plant roots (UNDERGROUND) - usually form MUTUALISTIC RELATIONSHIPS with plants - endophytic fungi are fungi that live in close association with ABOVE GROUND tissues of plants (stem and leaves)

In what circumstances will hyphae of zygomycetes that grow close to each other, combine in sexual reproduction?

If they are of different mating types - for instance, if they have different alleles of one or more genes (this is indicated by chemical messengers secreted by the hyphae) - in this way, mating types function as sexes - a single fungal species may have tens of thousands of sexes. This helps to generate genetic diversity in offspring, allowing fungi to fight off infections and adapt to environmental changes

The chytrids and zygomycetes form a...

Paraphyletic group (that is, like protists, they are not distinguished by a synapomorphy and they only represent some, not all, descendants of a single common ancestor) - what does this indicate about their evolutionary history? - swimming spores/gametes and the ability to make zygotes with tough outer coats evolved more than once in different species OR, both structures were present in the common ancestor, but were lost in certain lineages

T or F - the relationship between endophytes and grasses is mutualistic

T and F; endophytes produce compounds that benefit plants by deterring or even killing herbivores. In return, plants provide food. - however, some relationships form commensal relationships - they may simply coexist, with no effect on the host plant

T or F: fungi are more closely related to animals then they are to plants

T; Fungi and animals share a more recent common ancestor How do we know? - DNA sequence data - both animals and fungi synthesize CHITIN - fungal FLAGELLA (in chytrids) are similar to those in animals - both groups store glucose as glycogen (whereas plants store it as starch)

Why are reproductive organs (eg. Mushrooms, puffballs) of fungi not prone to drying out like the feeding structures?

The mycelia in the reproductive structures (ie. reproductive cells called spores) are DENSELY PACKED, THICK AND FLESHY (as opposed to thin and narrow), making them able to protect the mass of filaments on the inside from evaporation - they must be able to do this because usually they are the component of the fungi that is exposed above ground in the dry atmosphere

How do fungi digest food extracellularly?

They EXCRETE digestive enzymes which degrade the substrate outside the fungi. The digested food is then absorbed by the hyphae. - they do this because they can only absorb small particles

Plasmogamy

When the cytoplasm (in the case of fungi, hyphae) of two individuals fuse to form a single cell (in this case, hyphae with genetically distinct nuclei from each of the parents) - in humans, plasgomy occurs when the haploid sperm and egg fuse) - when the nuclei remain independent, the mycelium becomes heterokaryotic (dikaryotic is a type of heterokaryotic mycelium) - the distinct nuclei function independently

Karyogamy

when the pair of unlike nuclei fuse to form a diploid zygote - in humans, this occurs when the genetic material from the sperm cell fuses w the egg cell nucleus)

How do scientists distinguish each fungal group (ie. ascomycota, glomeromycota) as their own species?

- DNA sequencing - most groups are distinguished by their reproductive structures and type of LIFE CYCLE - eg. Glomeromycota make spores with a TOUGH OUTER COAT (this is their synapomorphy) - environment in which they can grow (some fungi can grow exclusively in a specific tissue type in a specific plant)

Which species of fungi can engage in parasitic relationships? Predatory relationships?

- Former question: microsporidia - they have polar tubes that can suck out nutrients from hosts - latter question: ascomycota can constrict their hyphae to trap roundworms and ingest them

Why are mycelia such an important part of fungi in terms of fungi being absorptive?

- Mycelia have a large surface area - the highest surface-area-to-volume ratio observed in a multicellular organism (note that although this increases absorption, it also makes them prone to drying out since the amount of water that evaporates form an organism is a function of its surface area)

What are hyphae?

- The individual, long, narrow filaments that make up a mycelium - less than 10 micrometres in diameter, allowing them to penetrate tiny fissures in soil and therefore, absorb nutrients that aren't accessible to plant roots - average lifespan of 5 days - may be haploid or dikaryotic, the latter meaning that each cell contains two haploid nuclei - one from each parent - fungi are made fully out of hyphae, but the hyphae are categorized as either the reproductive structure (dense hyphae) or the mycelium (spaced hyphae) which is the feeding structure - hyphae are divided into cell like compartments (thing of long tunnels with walls separating the tunnel into little rooms) by cross walls called SEPTA (s. Septum)

What does it mean when a fungus is coenocytic?

- This means that they lack septa entirely. - they have many nuclei scattered throughout the mycelium - they are basically a single, gigantic cell

Which species of fungi can completely degrade both lignin? How?

- basidiomycetes. They produce lignin peroxidase, an enzyme that catalyzes an an oxidation step that creates a free radical that leads to a series of uncontrollable reactions that split lignin polymers into smaller units (removal of a single electron from lignin) - called ENZYMATIC COMBUSTION

Characteristics of glomeromycota (includes arbuscular mycorrhizal fungi - AMF)

- form spores underground (asexual reproduction) - difficult to grow in the lab - vast ecological and economic important - assist plant growth by absorbing nutrients in the soil and transferring them to the plants)

Characteristics of ascomycota (cup fungi) - non-lichen-formers

- found in every terrestrial habitat and some freshwater and marine environments - can exist as both dikaroytic mycelia and yeasts - some form EMF associations with trees - most common endophytic fungi - some are saprophytic and parasitic forms are also common (they can capture roundworms using looped hyphae) - above ground, ascus bearing reproductive structure are called ascocarps and are cup-shaped - some are used to clean up contamination, they are used to make penicillin and yeast for alcohol and valuable foods like truffles and morels.