L13 Fungal Mutualists

Advantages of mutualism for fungi

"sweets for my sweet" -plants are an abundant source of sugars for the fungus

Arbuscular mycorrhizas: formation

*an infection process; however, extensive communication between the fungi and the root facilitates mutualism 1. spores germinate in response to root signaling molecules 2. hyphae penetrate the root tissues 3. hyphae grow between the cells in the root cortex and form appressoria that penetrate the plant cells 4. the host plasmalemma invaginates and proliferates around the fungus 5. repeated dichotomous branching of the fungal hyphae produces the arbuscule inside the cortical cell

Nutrient recycling: endophytes

initiate the biological degradation of dead or dying host-plant

lolines

powerful against invertebrates

Lichen naming

Fungal component: "mycobiont" Algal/cyanobacterial component: "photobiont" Scientific name is the same as that of the mycobiont

Photobiont

-90% green algae, 10% cyanobacterium -many are obligate symbionts -habitat may impact selection of photobiont by mycobiont

Mycobiont

-98% Ascomycota (40% are lichen formers), rest are Basidiomycota -1/5 of all fungi are obligate lichen formers -Communicate with photobiont using unique SMs Complex reproduction: -sexual mycobiont: fungal spores must find compatible photobiont upon germination and resynthesize the lichen symbiosis (horizontal transmission) -asexual mycobiont: photobiont is transmitted with the mycobiont through vegetative propegules or a fragmented thallus (vertical transmission)

Class 1 Endophytes

-Clavicipitaceous endophytes -fungal genera: Epichloe and Neotyphodium -resistricted to grasses -can grow in both above and below ground tissue

Arbuscule

-Highly branched bunch of hyphae within the plant root -Site of nutrient transfer between the plant and the fungus -4-15 day lifespan; upon death, they break down and the plant cell returns to normal

Endophytes: risks/benefits to the plant host

-Increase plant fitness by conferring stress tolerance -Decrease plant fitness by altering resource allocation

How do mycorrhizal fungi benefit plants?

-Increase the root SA (because they are smaller), allowing for better uptake of water and P, K, N (fungi can turn inorganic nitrogen into usable forms; NOT NITROGEN FIXERS THO) -Improve stress resistance -Protect against nematodes and disease -Protect against contaminant absorption -Enhance coil structure for increased water capacity and nutrient trapping -Promote faster rehabilitation of degraded sites -Improve biocontrol of pathogens

Arbuscular mycorrhizas: AM signals to host plants

-Lipo-chitooligosaccharides (LCO's) and chitooligosaccharides (CO's) -Chitin oligomers are present in all fungi and induce plant defense; however, when present in short chains (4-5) they perceive them as symbiotic signals and do not elicit a defense response

Endophytes: definition

-Microorganisms that internally infect living plant tissues without causing any visible manifestation of disease, and live in mutualistic association with plants for at least part of their life cycle

Mycorrhizal networks

-Most do not have host specificity -Most plant roots are colonized by multiple fungi -Plants are usually connected by mycorrhizal mycelial networks: "wood-wide-webs" -These networks facilitate transfer of carbon and nitrogen from one plant to another -form the worlds largest organism; 3.5 miles and 3 feet into the ground; 8,000 years old

Mycorrhizae

-Mutually beneficial relationship between plant roots and fungi -Mycorrhizae filaments in the soil function has extensions of root systems and are more effective at water and nutrient absorption than the roots themselves -Almost ALL terrestrial plant species carry and depend on mycorrhizae to some extent

immunosuppressive drugs

-Mycophenolic acid -used to prevent rejection in organ transplantation that was isolated from Penicillium brevicompactum

Arbuscular mycorrhizas: host plant signals to AM fungi

-Strigolactones are plant derived hormones that stimulate the branching and metabolism of presymbiotic hyphae in AM fungi -AM fungi perceive the strigolactones via a calcium-mediated pathway and activate multiple responses involving fungal cell wall metabolism -Cutin monomers: derived from the cuticle, make up the waxy coating of the leaf --> fungi perceive them as signals for producing "infections" of the roots

Lichens: benefit to fungus

-algae/cyanobacteria photosynthesizes to provide food for the fungus -provide benefit of nitrogen fixation

Lichens: important for nature and humans

-beautiful to look at -converse CO2 into O2, making them an important cleaner-upper of pollutants

biotic stress tolerance: endophytes

-by clavicipitaceous endophytes -enhane resistance to insect feeding and protect plants from herbivory through SMs

Non-clavicipitaceous (NC-endophytes; Non-Balansiaceous) endophytes

-can associate with a large array of different plant species -classes 2, 3, and 4

Classification of endophytes

-consist of mainly Ascomyctoa -two groups: 1. Clavicipitaceous (C-endophytes; Balansiaceous) 2. non-clavicipitaceous (NC-endophytes; Non-Balansiaceous)

abiotic stress tolerance: endophytes

-drought, metal contamination via chelation

Ectomycorrhiza (ECM) structural features

-form an extensive network of hyphae in the root cortex that makes the Hartig net -forms sheath of tissue around the outside of the root that extends into the soil: the fungal mantle -forms roots that are shorter and wider than uninfected roots

Class 1 endophytes: Epichloe endophytes

-form associations almost exclusively with grasses from the subfamily of Pooideae -host specific -grow intracellularly and systematically, infecting both vegetative and reproductive organs of their host plants including developing seeds -inherited vertically -provide protection against herbivores, enhance plant growth, photosynthetic rate, and stress tolerance -fungus receives nutrition, protection, and dispersion via host seeds -have successfully been developed and commercialized for agricultural use in the USA, Australia and New Zealand (example: MaxQ); increase vigor and growth

Lichens: benefit to algae

-fungi form protective cortex that protect the algae/cyanobacteria from UV rays -enables them to survive environments that could not otherwise

ergot alkaloids and indole diterpenes (lolitrem B)

-highly toxic to vertebrates -perennial ryegrass toxicosis from Neotyphodium endophytes

Ectomycorrhiza (ECM)

-hyphae grow between plant root cells -colonize only 10% of plant families, mostly woody plants -not host specific -most have above ground fruiting bodies but some have underground fruiting bodies, like a truffle -feed via hartig cells

Arbuscular mycorrhizas

-hyphae penetrate into the root cells -obligate biotrophs -only Glomeromycota -most common type of mycorrhizal association (80-90% of land plants) -Not very host specific -feed via arbuscule

Clavicipitaceous (C-endophytes; Balansiaceous) endophytes

-infect grasses -most common class 1 Epichloe + Neotyphodium

Class 1 endophytes: B. Neotyphodium endophytes

-mutualists with grasses, including important forage species -vertical transmission by growing into the forming seed and establishing resting mycelium in the embryo -produce alkaloid SMs: peramine, lolines, ergot alkaloids, and indole diterpenes

Photobiont switching

-mycobiont can associate with a new algal/cyanobacterial parter -allows for rapid adaption to the environment -allow lichen to acclimate

peramine

-no biotoxic effects -alkaloids -deters some invertebrates from feeding -produced by Neotyphodium

Why are we interested in endophytes?

-rich source of SMs -of high pharmaceutical, industrial, and agricultural importance Anticancer drugs, anti-fungal, anti-HIV, and other antimicrobial drugs, anti-cholesterol drugs, immunosuppressive drugs

Perennial ryegrass toxicosis aka "staggers" disease

-seasonal mycotoxicosis of grazing livestock -characterized by tremors, loss of coordination, convulsions, heat stress -death due to drowning

Ericoid mycorrhizae

-specialized to infect in the order of Ericales family or Ericaceae -form only endomycorrhizal associations -mostly colonize mature epidermal root hairs, penetrating them and filling them with coiled hyphae -It is through these coils that nutrient exchange occurs -80% of root volume can be fungal tissue -Ascomycota

Orchid mycorrhizae

-specialized to infect orchids -form mostly endomycorrhizal associations -most orchid seeds will not germinate unless they are infected -fungus may be the sole source of nutrition, particularly carbohydrates, needed for early development -Basidiomycota: "Rhizoctonia" (also known as plant pathogens)

Lichens

-symbiosis between fungi and green algae (85%), cyanobacteria (10%) or both (5%) -fungus is the dominant partner, determining shape and characteristics -green algae and cyanobacteria are photosynthetic

Endophytes: main characteristics

-ubiquitous in plants and have a profound impact on plant ecology, fitness, and evolution (like mycorrhizae) -reside entirely within the plant tissues and may grow within roots, stems, and/or leaves (unlike mycorrhizae) -can be transmitted vertically, horizontally, or both

Major types of Mycorrhizae

1. Endomycorrhizae or Arbuscular mycorrhizas (AM) -grow intracellularly -Glomeromycota -associated with 90%of plants 2. Ectomycorrhizae (ECM) -grow intercellularly -can be part of different categories -associate with 10% of plants

Endophytes vs. Mycorrhizas

1. Never see endophytes 2. Endophytes Can be above or below ground, mycorrhizae only associate with roots

Lolium perenne and Neotyphodium lolii

Lolium perenne: -"perennial ryegrass" -important grazing grass Neotyphodium lolii: -endophyte of perennial ryegrass -production of bioactive ergot alkaloids: ergovaline and lolitrem B (known to have toxic effects on mammals)

anti-fungal, anti-HIV, and other antimicrobial drugs

Micafungin: echinocandin antifungal isolated from Coleophoma empetri Altertoxin: a potent anti-HIV drug isolated from Alternaria tenuissima

Neotyphodium lolii mycotoxins

Neotyphodium endophyte Tremorgenic neurotoxins -cause incoordination by interference with neuronal transmission -"mimic" neurotransmitters like serotonin -induces heat stress and depresses prolactin levels, reducing milk yield Disease: perennial ryegrass staggers

Anticancer drugs

Paclitaxel: the world's first billion-dollar anticancer drug -isolated from Taxus brevifolia and Taxus wallinchiana, which harbor endophytic fungi Other anticancer drugs isolated from endophytic fungi including podophyllotoxin, kaempferol, torreyanic acid, and cajanol

anti-cholesterol drugs

Rosuvastatin, a statin isolated from Penicillium citrinum and P. brevicompactum

What happens when a mycorrhizae from one plant meets the mycorrhize from another plant?

a mushroom!

phytostimulation: endophytes

stimulate longer root hairs which makes more efficient absorption of essential nutrients