plant microbe associations

Question 1

Plant microbe associations

Answer 1

Positives:
Essential for C and N recycling
Important for plant growth (water and minerals)
Important to strengthen plant health

Negatives:
Detrimental to plant health
Threat to crop production for human food energy and energy
Threat to natural ecosystems

Question 2

what associations do plants form with roots

Answer 2

mutualistic, symbiotic

Question 3

what facilitates nutrient and water uptake

Answer 3

extensive fungal surface area

Question 4

symbiosis

Answer 4

mycorrhizal fungi

Question 5

what are mycorrhizal fungi

Answer 5

ecto or endomycorrhizal

Question 6

where do ectomycorrhizal fungi proliferate

Answer 6

outside the root and between cells

Question 7

where do endomycorrhizal fungi proliferate

Answer 7

within the cells

Question 8

what do EM fungi form surrounding the root

Answer 8

networks

Question 9

what does EMF form around the root tips

Answer 9

a mesh and also penetrate between the cells

Question 10

what is the name of the enzyme that bacteria use to fix nitrogen

Answer 10

nitrogenase

Question 11

Two-way signaling occurs between rhizobia and plant

Answer 11

1. The plant root produces a flavonoid chemical that attracts rhizobia
2. The bacterium produces a Nod factor, identifying it as a symbiont
3. The plant prepares to form a symbiotic nodule structure

Question 12

Symbionts

Answer 12

• Fungi and bacteria
• Fungal associations very old – helped colonise land
• Help to provide water and minerals
• Help to fix nitrogen (natural fertilizer for legumes)
• Receive carbon compounds (e.g. sugars) fromphotosynthesis

Question 13

Saprophytes

Answer 13

Feed off dead/organic matter (plant and animal)* Fungi and bacteria
* Digest then absorb
* Extracellular (secreted) enzymes
* Carbohydratases, lipases, proteases
* Essential for N and C recycling

Question 14

what must a successful pathogen do

Answer 14

*Find the host and attach to it
*Gain entry through the plant’s impermeable defenses
*Avoid the plant’s defense responses
*Grow and reproduce
*Spread to other plants

Question 15

Plants are exposed to countless microbes, but very, very few of these interactions lead to disease. Why?

Answer 15

The pathogen must be able to overcome plant defense

The host plant must be susceptible to the pathogen

The environment must tip the balance in favor of the pathogen

Question 16

Facultative

Answer 16

pathogens can attack living plant cells but can also grow by themselves, e.g. on artificial medium

Question 17

Obligate

Answer 17

can only grow on their specific living host

Question 18

Biotrophic

Answer 18

feed on living plant tissue, not causing cell deathexample=Hyaloperonospora arabidopsidis (oomycete)

Question 19

Necrotrophic

Answer 19

kill plant cells and then feedexample=Botrytis cinerea (fungus)

Question 20

Hemibiotrophic

Answer 20

initially biotrophic and then become necrotrophicexample=Pseudomonas syringe (bacteria)

Question 21

Biotrophs

Answer 21

*“Pretend harmony”
*Fewer cell wall-degrading enzymes than non-biotrophs
*Evade detection and avoid limitation of defense responses

Question 22

Necrotrophs

Answer 22

*“Smash and grab”
*Produce toxins and cell wall-degrading enzymes

Question 23

what do Root-knot nematodes do

Answer 23

induce expansion in five to seven neighboring cells to produce giant cells

Question 24

what do cyst nematodes do

Answer 24

partially dissolve cell walls between cells to produce syncytium

Question 25

what do nematode effectors do in general

Answer 25

modify root cells to become specialised feeding cells

Question 26

what is Hyaloperonospora arabidopsidis

Answer 26

it’s a biotrophic biotrophic oomycete that infects Arabidopsis

Question 27

what does fungal and oomycete (hemi)biotrophs usually make

Answer 27

haustoria

Question 28

what is haustoria

Answer 28

In botany and mycology, a haustorium is a rootlike structure that grows into or around another structure to absorb water or nutrients

Question 29

where do Haustoria remain

Answer 29

outside the plant plasma membrane, and are specialized for nutrient and signal exchange

Question 30

How do plant cells detect microbes?

Answer 30

receptor proteins on the surface of plant cells

Question 31

How do they defend themselves?

Answer 31

recognize microbe-associated molecular patterns (MAMPs) of potential pathogens through pattern recognition receptors (PRRs) that mediate a basal defense response.

Question 32

how do pathogens overcome the plant immune system

Answer 32

To cope with plant immunity, pathogens have evolved mechanisms to deliver effector proteins into plant cell, which target and inhibits immune signaling, as well as to subvert immunity through targeting of critical host cellular processes

Question 33

How do plants then defend themselves from pathogens that can infect them?

Answer 33

Various natural compounds, ranging from cell wall components to metabolic enzymes