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APS 276- Symbiosis > seminar 4: Ton > Flashcards

seminar 4: Ton Flashcards

1
Q

what is take all disease also known as?

A

G.graminis

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2
Q

what was done in the 1960s field trial USA looking at take all disease suppression by crop rotation? (4)

A
  • control plot with same wheat crop grown over the years
  • after 7 years monoculture disease severity peaked
  • after 15 years disease severity leveled out at low acceptable level
  • biological origin causing the disease
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3
Q

what 4 bacteria are responsible to take all disease suppression and which of these strains promotes plant growth?

A
  • P.fluorescens
  • P.putida
  • Enterobacter species
  • B.subtilis (promotes plant growth)
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4
Q

in what 3 main ways do plant growth promoting rhizobacteria (PGPR) promote plant growth?

A
  1. induced changes in root morphology
  2. facilitating nutrient uptake
  3. plant disease suppression
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5
Q

how do induced changes in root morphology promote plant growth?

A
  1. induce plant growth hormones
    - auxin growth promoting
  2. inhibit plant growth repressing hormones
    - ethylene: causes senescence
    - ACC deaminase used to inhibit ethylene
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6
Q

in what 3 main ways does PGPR suppress plant disease?

A
  1. direct antibiosis
  2. competition for iron
  3. induction of systemic resistance (ISR)
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7
Q

what is direct antibiosis?

A

cant grow fungi near bacterial colony as compounds toxic to fungus

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8
Q

how may iron competition reduce plant growth?

A
  • rhizobacteria may steal iron from other fungi and outcompete
  • fluorescent siderophores produced that bind with high affinity to iron
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9
Q

what does ISR do?

A
  • protects plant from pathogen and herbivores

- can change immune status of host plant

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10
Q

in Arabidopsis what can PGPR induce?

A

resistance against pests and disease

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11
Q

when leaves are infected how do caterpillars perform?

A

worse and grow slower therefore plant is better protected

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12
Q

when testing for leaf spot disease what was found for the P.fluorescens infected plant?

A

spreads less

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13
Q

why must the plant have lots of defence mechanisms?

A

lots of mechanisms used to cause disease and have to fight off lots of different attackers

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14
Q

what is the protection like for plants grown in soil enriched with PGPR?

A

more protected

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15
Q

induced defence in plants is costly how is this shown in Arabidopsis?

A

may be resistant but growth is stunted as investing lots into defence mechanisms

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16
Q

what is immune priming? (4)

A
  • immunological memory
  • intermediate stage if defence allowing bacteria to prime
  • allows them to develop a stronger immune response after pathogen attack
  • induced resistance
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17
Q

list the 4 main signalling pathways controlling P.fluorescens in induced defence priming

A

MYB72
BGL42
MYC2
ABA1

18
Q

what is/does it do: MYB72?

A

transcription factor in roots tricking plants into thinking they are iron deprived so exudes other root exudates

19
Q

what is/does it do: BGL42?

A

second to act

B-glucosidase hydrolytic enzyme that can cleave glucose and activate secondary metabolites

20
Q

what is/does it do: MYC2?

A
  • in leaves priming depends on this transcription factor

- jasmonic acid defence genes activated

21
Q

what does jasmonic acid gene activate?

A

inducible defences against herbivores and necrotrophic fungi

22
Q

what is/does it do: ABA1?

A

primes cell wall defence

- better defence if grown in presence of P.fluorescens

23
Q

involving P.putida what happens when SerPIN proteins accumulate in leaves ?

A

leaves less nutritionally beneficial to caterpillars so eaten by less

24
Q

briefly what is the step by step for priming by root colonisation of P.putida on maize? (4)

A
  1. bacteria activates signal priming shoot for antiherbivore defences under jasmonic acid control
  2. SerPIN proteins accumulate
  3. sensitised leading to augmented expression
  4. emit airborne compounds/inducible volatiles
25
Q

what do inducible volatiles do?

A

immobilise other organisms by attracting other insects to attack caterpillars

26
Q

what do signals plants use to obtain beneficial bacteria use?

A

root exudation chemistry

- secrete complex metabolites

27
Q

what is DIMBOA? (4)

A
  • secondary metabolite
  • high levels in young seedlings but reduces over time
  • selective activity
  • can kill off pathogens
28
Q

when growing the plant at increasing concentrations of DIMBOA what was found?

A
  • P.putida could still grow as very tolerant
29
Q

what does DIMBOA induce in p.putida?

A

chemotaxis

30
Q

when carrying out a DIMBOA induced transcriptome what was discovered?

A

lots of genes upregulated

- most involved in breakdown of aromatic compounds including DIMBOA

31
Q

what is chemotaxis?

A

microbe behavioural response to chemical stimulus and can move towards or away from it

32
Q

what kind of signal can DIMBOA act as for bacteria?

A

recruitment

could activate cells to be attracted to the source

33
Q

what kind of compound is DIMBOA?

A

BX

34
Q

what could the created BX1 mutant not do?

A

produce BX compounds such as DIMBOA

35
Q

what was found when grew wild type and BX1 mutant on non sterile agar plate ?

A

lower fluorescence in BX1 mutant so less able to sustain growth by P.putida

36
Q

what did the BX6 mutation do?

A

DIBOA-> DIMBOA obstructed

so more DIBOA

37
Q

what are crown roots?

A

take up nutrients and act as storage organs

- more DIBOA and DIMBOA in these roots

38
Q

what are bacterial species referred to as?

A

operational taxonomic units

39
Q

what are the 4 main stages for microbial community analysis by sequencing rRNA genes?

A
  1. DNA extracted from microbes in rhizosphere
  2. primers amplify variable internal transcribed spacer ITS2 between conserved rRNA genes
  3. PCR to study taxonomy
  4. sequence
40
Q

when looking at the effect on OTUs what was the colour difference between primary and crown roots like for BX1 and BX2 mutants?
- how does this compare to BX6 mutants?

A

strong
more BX in crown roots
- less intense impact on community structure

41
Q

what were the predicted breakdown products from DIBOA and DIMBOA?

A

(M)BOA

42
Q

what did the follow on study by Hu et al do/find? ()

A
  • wildtype BX+ and mutant BX-
  • plants growing on soil conditioned on wild type better protected from herbivory than those conditioned with mutant
  • Bacteria under control of secondary metabolites of BXhave long lasting effect on soil health can can benefit further generations of plants

APS 276- Symbiosis (29 decks)

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