Lecture 13 - Microbe-Plant Interactions

Question 1

What are the 2 types of microbe-plant associations that plants benefit from?

Answer 1

mutualistic and commensalism

Question 2

What are some examples of mutualistic activities between plant-microbe interactions?

Answer 2

they are highly specialized such as fungal interaction with root system or bacteria producing nodules

Question 3

Where do most plant-microbe interactions occur?

Answer 3

in the rhizosphere

Question 4

What is a rhizosphere?

Answer 4

soil bits still attached to plant’s roots

Question 5

What are the 3 different groups of microbes found in the rhizosphere?

Answer 5

beneficial, commensal, and pathogenic

Question 6

How does a beneficial microbe interact with the plant within the rhizosphere?

Answer 6

mutualistic interaction, it uses nutrients released from plant roots

Question 7

How does a commensal microbe interact with the plant within the rhizosphere?

Answer 7

plant doesn’t benefit (researchers claim) but organism benefits from released nutrients of plant

Question 8

How does a pathogenic microbe interact with the plant within the rhizosphere?

Answer 8

benefits from released nutrients of plant but has negative affect on plant, commensal and/or beneficial microbes

Question 9

What type of interaction is between the water fern and cyanobacteria? (positive or negative?

Answer 9

positive

Question 10

How can water ferns be used as a biofertilizer?

Answer 10

considered as “green manure” because it is nitrogen rich

Question 11

Explain the interaction between water ferns and cyanobacteria. Who benefits what?

Answer 11

cyanobacteria grow in the cavities/holes on water fern leaves as well as provides it nutrients and sugars IN TURN cyanobacteria fixes N2 to NH3 for water fern

Question 12

What are mycorrhizae? What type of interaction is this?

Answer 12

relationship between fungus and root and are endo- or ectomycorrhizae | mutualistic interaction

Question 13

Which is more prevalent in the rhizosphere? Gram+ or Gram–

Answer 13

gram–

Question 14

What are the 3 benefits of mycorrhizae?

Answer 14

make plants capable of survival in low-nutrient soils, higher plant growth rates, more disease-resistance

Question 15

What are ectomycorrhizae?

Answer 15

fungus is associated with roots which are shorter, thicker, and more branched | no breaking of root cells

Question 16

What are the structures that develop the ectomycorrhizae?

Answer 16

Hartig nets and fungal sheath

Question 17

What are Hartig nets?

Answer 17

where the fungus has gone in and surrounds root cells

Question 18

What are fungal sheaths?

Answer 18

what surrounds the whole root

Question 19

Explain the ectomycorrhizae interaction. Who benefits what?

Answer 19

fungus provides essential nutrients/minerals for plant IN TURN plant provides sugars for fungus

Question 20

Where are ectomycorrhizae commonly seen in (type of plants)?

Answer 20

trees

Question 21

What are endomycorrhizae?

Answer 21

fungus penetrates root cells via arbuscules

Question 22

What are arbuscules?

Answer 22

fungal structures used to uptake nutrients

Question 23

What is the benefit of the arbuscule penetration of root cells?

Answer 23

enhanced root uptake of minerals

Question 24

Explain the endomycorrhizal interaction. Who benefits what?

Answer 24

endomycorrhizal fungus provides plant with nutrients/minerals and enhances uptake IN TURN plant provides sugars for fungus

Question 25

Which mycorrhizae is more common, endo- or ecto-?

Answer 25

endomycorrhizae

Question 26

What are hyphae?

Answer 26

branching filaments of fungal cells

Question 27

Which organisms are the only ones that contain nitrogen fixation genes?

Answer 27

prokaryotes (ONLY)

Question 28

What is nitrogen fixation?

Answer 28

taking nitrogen from the atmosphere and fixing it into ammonia

Question 29

Within mutualistic plant-bacteria interactions, what does the plant usually provide?

Answer 29

carbon and energy sources

Question 30

Within mutualistic plant-bacteria interactions, what do the bacteria usually provide?

Answer 30

fix nitrogen for amino acid production within plants

Question 31

What is the 5-step nodule formation by rhizobia?

Answer 31

bacteria attach to plant root hairs >>> Shepherd's crook forms = stimulates bacteria to infect root >>> bacteria creates infection thread up to the root >>> thread branches and bacteria enters plant cell walls >>> bacteria loses cell wall

Question 32

What is Shepherd's crook?

Answer 32

when plant root hair curls around the bacteria

Question 33

What is an infection thread?

Answer 33

where the bacteria crawls up the root

Question 34

What are bacteroids?

Answer 34

bacteria without a cell wall within a host cell

Question 35

How do the bacteria stimulate plant root growth? What does it result in?

Answer 35

it releases molecules that stimulate growth = results in tumor

Question 36

What are plant "tumors"?

Answer 36

nodule-like structure filled with bacteroids

Question 37

What is the purpose of bacteroids in a plant nodule?

Answer 37

solely to fix nitrogen for plant

Question 38

What attracts the bacteria to the plant root?

Answer 38

flavenoids

Question 39

What are flavonoids?

Answer 39

molecules plant releases

Question 40

What are nod genes?

Answer 40

genes within the bacteria that result in proteins in the bacteria that will be recognizable to nod-factor receptors

Question 41

What is the function of flavonoids?

Answer 41

to induce transcription of nod genes

Question 42

What are nod-factor receptors? What does it stimulate?

Answer 42

present on root hairs and stimulates the formation of Shepherd's crook (root hair curling)

Question 43

What are the effects of the infection thread (3 effects)?

Answer 43

releases effectors, releases phytohormones, and activate plant's immune system

Question 44

What happens when the infection thread activates the plant's immune system?

Answer 44

plant will try to fight bacterial infection and prevent nodulation because its foreign

Question 45

What are phytohormones and what do they do?

Answer 45

plant hormones induce plant cell division

Question 46

What is leg hemoglobin?

Answer 46

molecule that surrounds roots and binds to O2

Question 47

What is the function of leg hemoglobin?

Answer 47

to bind to any O2 that enters its anaerobic environment

Question 48

What is nitrogenase?

Answer 48

enzyme that converts nitrogen into ammonia

Question 49

What is the function of nod genes?

Answer 49

transcribe proteins to create infection thread

Question 50

What inactivates nitrogenase? Where is nitrogenase found (type of environment)?

Answer 50

oxygen | found in anaerobic environments

Question 51

Which plant structure prevents O2 from entering?

Answer 51

root nodules

Question 52

What does nitrogen-fixation help produce in legume nodules?

Answer 52

glutamine

Question 53

Where is glutamine transported by and to in legumes?

Answer 53

by the root hairs to regions of protein synthesis

Question 54

What are rhizobacteria?

Answer 54

term for a bacterial species that lives in rhizosphere

Question 55

What is PGPR?

Answer 55

plant-growth-promoting rhizobacteria (most rhizobacteria)

Question 56

What makes most rhizobacteria plant-growth-promoting?

Answer 56

they can produce plant-like hormones

Question 57

What do the plant-growth-promoting rhizobacteria use the hormones to do?

Answer 57

initiate root symbiosis

Question 58

What are 2 effects plant-growth-promoting rhizobacteria have on plants?

Answer 58

positive-direct affect via N2-fixation and phytohormones | negative indirect affect on pathogens via siderophore and antibiotic production

Question 59

What is a siderophore?

Answer 59

protein that sequesters iron

Question 60

How would siderophores be detrimental against pathogens?

Answer 60

not enough iron available for pathogens to use (all organisms and cells need iron)

Question 61

What are the 4 detrimental activities microbes do/have on plants?

Answer 61

fungal parasites, bacterial pathogens, viruses, and rhizosphere activities/plant disease

Question 62

What are 2 examples of fungal parasite causing plant diseases?

Answer 62

dutch elm (fungus transported by beetles) and potato blight

Question 63

What is the mode of pathogenesis with fungal parasites?

Answer 63

spores contact plants >>> fungi penetrates surface >>> intracellular infection >>> pathogen spreads within plant >>> death = days to weeks

Question 64

How do bacterial pathogens penetrate plant's thick cell wall?

Answer 64

evolved different mechanisms such as use of secretion systems releasing enzymes to degrade cell wall or infect the root structures

Question 65

What are 2 examples of plant diseases caused by bacterial pathogens?

Answer 65

crown gall disease and alfalfa wilt

Question 66

What are the 2 major modes of viral transmission on plants?

Answer 66

getting infected and infected from a parent (verticle transmission)

Question 67

Explain the fungal trapping of nematodes. :(

Answer 67

fungus produces ring structure that traps nematode >>> hyphae comes out of fungus and starts eating nematode from the inside