Plant-fungal Interactions

Question 1

Beneficial/neutral

Answer 1

Fungal endophytes
Mycorrhizal fungi

Question 2

Detrimental

Answer 2

Pathogenic

Question 3

Importance of beneficial plant-fungal symbioses

Answer 3

Present in all (endophytes) or most (mycorrhizas) plants
Usually improve plant growth
Source of active secondary metabolites: antimicrobial and antibacterial activities

Question 4

Fungal endophytes

Answer 4

Live asymptomatically (without causing any apparent tissue damage) within plant tissues, emerging to sporulate at plant or host-tissue senescence
Colonise angiosperms, liverworts, hornworts, mosses, ferns…
Found in all ecosystems, from the arctic to the tropics
Increase tolerance to drought, disease, herbivory and parasitism through production of fungal secondary metabolites

Question 5

Epichloë/Neotyphodium spp (Ascomycota)

Answer 5

Mutualistic associations with temperate grasses
Increased tolerance to drought, disease, herbivory and parasitism through production of fungal secondary metabolites
Infiltrate the seeds and inherited vertically

Question 6

Dark septate endophytes (Ascomycota)

Answer 6

In roots of most plants, have negative to positive effects on hosts
More abundant in stressed environments
Most of their biology and ecology are unknown

Question 7

Mycorrhizal symbioses

Answer 7

Mutualistic relationship between plants and soil fungi
Plant gives C to the fungus
Fungus gives nutrients and water to the plant

Question 8

5 main types of mycorrhizal fungi

Answer 8

Ectomycorrhizae
Arbuscular mycorrhizae
Ectendomycorrhizae
Ericoid mycorrhizae
Orchid mycorrhizae

Question 9

Arbuscular mycorrhizas (AM):

Answer 9

Glomeromycota, ~240 species described
Bryophyta, pteridophytes, gymnosperms, angiosperms

External hyphae: scavenge the soil and absorb nutrients  enhanced nutrient acquisition
Produce spores
Produce extraradical hyphae outside of the plant
Penetrate plant cells using arbuscule

Question 10

Ectomycorrhizas (EM):

Answer 10

Basidiomycota, Ascomycota, 5000 – 6000 species.
Gymnosperms, angiosperms (almost all are woody perennials).

A lot of external hyphae (fungal mantle) surrounding the roots
Do not penetrate plant cells

Question 11

Mantle

Answer 11

layers of fungal hyphae covering the root surface

Question 12

Hartig net

Answer 12

hyphae penetrate between host cells and branch to form a labyrinthine structure

Question 13

Ericoid mycorrhiza:

Answer 13

Ascomycota
- Ericales, Bryophytes — heathers, lingonberries
Penetrate plant cells using pelotons

Question 14

Arbutoid mycorrhiza:

Answer 14

Basidiomycota
- Ericales

Question 15

Monotropoid mycorrhizas:

Answer 15

Basidiomycota associated with Monotropoideae (within Order Ericales):

Small seeds, require fungal colonization for embryo development
Achlorophyllous - monotropoid roots use mycorrhizal fungi to take C from nearby plants

Question 16

Orchid mycorrhizas

Answer 16

Basidiomycota associated with Orchidaceae
Require mycorrhizal fungi colonization for developing seedlings as seeds are so small
- autotrophic orchids (with chlorophyll): fungus provides carbon until leaves are present
- mycoheterotrophic orchids (achlorophyllous): fungus provides carbon during all plant life

Penetrate plant cells using pelotons

Question 17

How do plants usually benefit from mycorrhizal fungi

Answer 17

Improved nutrient uptake (mainly P and N)
Increased soil stability
Provide resistance against pathogens and herbivores
Improve water balance
Alleviate abiotic stresses (salt, pH, heavy metals…)
…

Question 18

Transporters from soil to fungus

Answer 18

Pi transporter
NH4 + transporter
NO3 transporter
AA transporter
Urea transporter

Question 19

Transporters from fungus to plant

Answer 19

Pi transporter
NH3/NH4 + transporter
Hexose transporter

Question 20

Classification of fungi

Answer 20

Glomeromycota
Asomycota
Basidiomycota

Question 21

What kind of mycorrhizae is glomeromycota

Answer 21

Arbuscular mycorrhizae

Question 22

Number of mycorrhizal types overall

Answer 22

7

Question 23

Ectendomycorrhizae

Answer 23

Penetrate cells using pelotons

Question 24

How are mycorrhizae classified

Answer 24

Fungi septate or aseptate
Intracellular colonisation
Fungal mantle
Hartig net
Achlorophylly
Fungal taxa
Plant taxa

Question 25

Where do hyphae never penetrate

Answer 25

Endodermis

Question 27

Nutrient transfer - arbuscular mycorrhizae

Answer 27

Fungus penetrates plant cells without penetrating cell membrane Arbuscules

Question 28

Nutrient transfer - ectomycorrhizas

Answer 28

Hartig net around outside of cells

Question 29

Nutrient transfer - ericoid/arbutoid/ectendomycorrhizas/orchid/monotropid

Answer 29

Pelotons to penetrate cells

Question 30

Plant fungal diseases as a threat to food security

Answer 30

~ 10% of agricultural production is lost annually due to fungi ~ 10,000 species of fungi are known to cause disease to plants

Question 31

Symptoms caused by pathogenic fungi

Answer 31

Leaf spots: localised lesions consisting on dead and collapsed cells Blight: general and extremely rapid browning and death of leaves, branches, twigs or floral organs Dieback: extensive necrosis of twigs beginning at their tips Root rot, soft rot, and dry rot: disintegration or decay or part or all of the root system Damping off: rapid death and collapse on very young seedlings Canker: localised necrotic lesion on a stem or fleshy organ

Question 32

Why are fungi good pathogens

Answer 32

High reproductive potential during the main growing season Long-term survival: as free-living saprophytes or as spores Haploid genome permits adaptive mutations to be selected for Efficient dispersal mechanisms by wind, water or vectors:

Question 33

Pathogenic fungal life cycle

Answer 33

1. Entry of the host 2. Nutrient acquisition 3. Reproduction

Question 34

Entry of the host (infection)

Answer 34

Subcuticular Ephphytic Intracellular Intercellular Vascular Can occur via wounds, natural openings (eg stomata) or direct penetration

Question 35

Adherence

Answer 35

some spores carry adhesive substances. In some cases an adhesion pad forms and cutinase and cellulase enzymes are released from the spore to help with adherence

Question 36

Apressorium formation

Answer 36

the tip of the hyphae increases and forms a flattered, bulb-like structure to increase the area of adherence and securely fastens the pathogen to the plant. Cutinases and pectinases are produced. Can form in response to topographical (e.g. stomata), chemical (e.g. epicuticular waxes) or physical (hydrophobicity or thigmotropism)

Question 37

Penetration peg

Answer 37

from the appressorium, a fine growing point, called the penetration peg, forms. Penetration is assisted by enzymes that softens or dissolve the barriers.

Question 38

Nutrient acquisition

Answer 38

Many fungi form haustoria (sing. haustorium), modified hyphae that penetrate through the plant cell wall and expands inside the cell, to acquire nutrients

Question 39

Nectrotrophic species

Answer 39

produce host-selective toxins that inactivate plant processes causing cell death in advance of infection

Question 40

Biotrophic species

Answer 40

usually alters plant metabolism and development but plant cells remain alive in advance of infection

Question 41

Hemibiotrophic species

Answer 41

the pathogen initially keeps cells alive but at later stages of the infection, kills them

Question 42

Reproduction

Answer 42

Spore production and dissemination

Question 43

Plant defences- before entry

Answer 43

Leaf and root exudates may stimulate or inhibit germination and/or growth of the pathogen Physical barriers may prevent infection (waxes in cuticle, suberin and cutin in roots)

Question 44

Plant defences - after entry

Answer 44

P/MAMPs: lipopolysaccharides, flagellin, chitin PTI: P/MAMP-triggered immunity ETI: Effectors often suppress PTI but some are recognised by nucleotide-binding proteins (NB-LRR), which induce the effector-triggered immunity

Question 45

Induced defence

Answer 45

Deposition of callose in cell walls to reinforce the plant cell wall and/or physically mask fungal presence Accumulation of phytoalexins, low molecular weight antimicrobial compounds Hormonal changes: salicylic acid (SA), jasmonic acid (JA) and ethylene accumulation Activation of plant resistance genes with accumulation of reactive oxygen intermediates and ion channels Activated protein synthesis leading to antimicrobial compounds production (proteinases, chitinases, glucanases) that damage pathogen structures

Question 46

Claviceps purpurea (ergotism) Ascomycota

Answer 46

Infects rye and other cereals Ingestion of the alkaloids produces convulsive symptoms and dry gangrene. In middle ages, a massive human poisoning killed >40000 people in France (Saint Anthony’s fire).

Question 47

Phytophtora infestans (potato blight) Oomycota

Answer 47

Irish potato famine 1840s, reduced the population of Ireland from 8 to 5 million in just 3 years through starvation and emigration.

Question 48

Magnaporthe oryzae (rice blast disease) Ascomycota

Answer 48

Infects rice, barley, wheat and millet Used as model species to study host-fungal interactions

Question 49

Botritys cinerea (grey mould) Ascomycota

Answer 49

Infects more than 200 plant species, necrothroph

Question 50

Puccinia spp (rusts) Basidiomycota

Answer 50

Several species, infect wheat

Question 51

Fusarium graminearum (Head blight and crown rot disease) Ascomycota

Answer 51

Infect several important cereal species. Results in mycotoxin-contaminated grain.

Question 52

Microbotryum violaceum (anther smut disease) Basidiomycota

Answer 52

Obligate parasite of Caryophyllaceae Plant sexually transmitted disease, causes plant sterility.

Question 53

Rhizoctonia solani (root rot disease) Basidiomycota

Question 54

What kind of wounds can fungi enter through

Answer 54

Abscission scars Lateral roots Abrasions Vector bites

Question 55

What kind of natural openings can fungi enter through

Answer 55

Stomata Lenticels Glands, hydathodes, nectaries

Question 56

How can fungi enter via direct penetration

Answer 56

Cuticle Epidermis Vulnerable sites, eg stigma

Question 57

Role of Trichomes in plant defence

Answer 57

Contribute to leaf spatial organisation and may pose preferable site of penetration Prevent the fungal spore from reaching the leaf surface

Question 58

Role of cuticle in plant defence

Answer 58

Components of cuticle constitue signals for infection Cuticle functions as a protective layer

Question 59

Role of callose in plant defence

Answer 59

Callose fortifies the cell wall limiting fungal spread Callose may protect the pathogen from plant defence machinery