Symbiosis

Symbiosis

close and prolonged biological association between two or more organisms

Obligate Symbiosis

at least one partner depends on the other partner(s) for survival

Facultative Symbiosis

a partner can live without the other partner

Parasitism

one partner (usually pathogen) benefits, other partner (host) is harmed

Commensalism

one partner benefits, other partners are not harmed or helped

Fungi Characteristics

• filamentous growth (hyphae)

• heterotrophic

Hyphae

filamentous growth in fungi

Mycelium

mass of hyphae in fungi

Hyphae Characteristics

• chitin cell walls

• divided by crosswalls (septa)

Chitiin

polysaccharide

• acetylglusomine subunits with both carbon and nitrogen

Septa

central pore = allow protoplasts of adjacent cells to be connected

aseptate

no crosswalls

Heterotrophic

cannot synthesis organic nutrients

Heterotrophic Mutalists

acquire organic materials from living hosts

Heterotrophic Biotroph Parasites

Acquire organic materials from living host cells (usually slowly) = harms host

Heterotrophic Necrotroph Parasites

Acquire organic materials from host by killing host cells, then absorbing released nutrients

Heterotrophic Saprotroph

acquire organic materials from dead organisms

• contribute to decomposition and nutrient cycling

Spores

one-celled/two-celled reproductive structures capable of growing into new organism without fusion with another cell

Asexual Fungi

mitosis → mitospores

Sexual Fungi

meiosis → meiospores

Basidiomycota

mushrooms, mycorrhizal symbionts

Ascomycota

molds & some mycorrhizal symbionts

Dikarya

basidiomycota + ascomycota

• distinct nuclei (n+n) = two haploid (n) nuclei with shared cytoplasm

Glomeromycota

mycorrhizal species (few species)

Polypore Fungi

typically grow within trees, have large fruiting bodies with spore producing pores underneath

• Ex. Diamond willow fungi, tinder fungus (chaga)

• can cause wood decay

Mycorrhizae

fungus plant mutualism

Lichens

fungi-algae or fungi-cyanobacteria mutualism

Conidiogenesis

asexual production of spores called conidia

Conidia

• arise from mitotic divisions of hyphal cells

• NOT PROD INSIDE STRUC

  • most common in ascomycota, less common in basidiomycota

Fungi Sexual Reproduction

1. Plasmogamy

2. Karyogamy

3. Meiosis

Plasmogamy

hyphae of two distinct genotypes come together → protoplast fuse → dikaryon

Karyogamy

fusion of two haploid nuclei = diploid zygote nucleus (2n)

Meiosis

produces haploid spores (n)

• typically spores germinate when they contact food source = haploid hyphae

Ascomata/Ascocarp

visible body that undergoes sexual reproduction in ascomycotaa

• can be open or closed

Cleistothecium

enclosed ascoma

Perithecium

open flask-shaped ascoma

Apothecium

open saucer-shaped ascoma

Ascus

where karyogamy takes places = spore producing structure

Gametangia

body in which gametes are produced

• ascogonia and antheridia

Ascogonium

produces trichogyne outgrowth that bridges protoplasts

Croziers

develop from ascogenous hyphae on inner surface of ascoma = hymenium (hook)

Basidioma/Basidocarp

visible part of fungus in basidiomycota sexual reproduction

Clamp connections

apical cells of dikaryotic mycelia divide and form these to enabled distribution of parent nuclei

Basidia

spore forming structures on surface of basidioma

Endophytes

have cryptic symbiosisc

cryptic symbiosis

fungi that penetrate and persist within healthy abovegrpund tissues, such as leaves, but colonized plants appear asymptomatic

Ectomycorrhizae

• Hartwig Net + mantle

• mostly Basidiomycota

• trees and shrubs from temperate regions

Hartig Net

penetration of hyphae between cell walls of cortex cells in the root

• does not enter vascular cylinder

Mantle

hyphal mat on surface of root

Arbuscular Mycorrhizae (AM)

• all invovle division of glomermycota

  • obligate symbiotic

Arbuscules

branched structures invaginate plant plasma membrane = extensive contact with plasma membrane of root cell

• don’t enter cytoplasm

Vesicles

thin walled balloon type storage structures

Orchid Mycorrhizae

• tiny seeds with few nutrients

• Basidiomycota invaginate PM of host root cells = unique peleton coils

Lichens Structure

• Mycobiont partner (fungi)

• Photobiont (photosynthetic)

  • mutualistic

• polyphyletic (no common ancestors)

Thallus

body of lichen

• lacks vascular tissue

  • not differentiated in root, stem, or leaf

Upper Cortex

protective surface of tightly packed fungal hyphae

Lower Cortex

also composed of fungal hypae

medulla

loosely packed fungal hyphae

Soredia

small propagules containing mycobiont and photobiont partners that can be dispersed

Rhizine

anchorage only, not absorption

Since Lichens Lack Cuticle + Stomata

• sensitive to pollution (sulfur dioxide)

• long lived = cumulative effects

• can be used as bioindicators

Pathogens

must grow inside another organism in order to complete part or all of their lifecycle = negative effects on host

Disease

abnormal growth of dysfunction of an organism due to the influences of a causal agent

Symptoms

visible manifestations of disease

Hemi biotroph Pathogens

obtain nutrients from living host cells during initial colonization phase - then switch to killing host cells for nutrients

The Disease Traingle

1. How virulent is pathogen?

2. How susceptible/resistant is the plant?

3. Do environmental conditions favour pathogen growth or plant defense?

5 Outcomes of Pathogen-Plant Interaction

1. Environmental conditions change (pathogen dies)

2. Attacked plant species is a non-host (plant is resistant)

3. Plant has preformed defenses like structural barriers or toxic compounds (plant prevents infection)

4. Attacking pathogen is recognized by the plants surveillance mechanism (plant is resistant)

5. Invasion Successful

PAMPs

Pathogen-associated molecular patterns

• molecules produced by pathogen that are unique from molecules produced by host

  • can be recognized by host

Pattern Recognition Receptor (PRP)

plasma membrane-embedded receptor that can bind fungal-derived PAMPs

PAMP-triggered immunity (PTI)

rapid response triggered by PRP binding PAMP = string defense = plant is resistant

Effectors

secreted by pathogen into host cells

• pathogens strategy to block hosts defenses

  • override plants defense response = infection

ETI = Effector Triggered Immunity

pant detection of pathogen-secreted effectors through intracellular receptors

• works in tandem with PTI to confer resistance

Jasmonate

defense hormone triggered by necrotrophs

Salicylate

defense hormone triggered by biotrophs