seminar 4: Ton Flashcards
what is take all disease also known as?
G.graminis
what was done in the 1960s field trial USA looking at take all disease suppression by crop rotation? (4)
- 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
what 4 bacteria are responsible to take all disease suppression and which of these strains promotes plant growth?
- P.fluorescens
- P.putida
- Enterobacter species
- B.subtilis (promotes plant growth)
in what 3 main ways do plant growth promoting rhizobacteria (PGPR) promote plant growth?
- induced changes in root morphology
- facilitating nutrient uptake
- plant disease suppression
how do induced changes in root morphology promote plant growth?
- induce plant growth hormones
- auxin growth promoting - inhibit plant growth repressing hormones
- ethylene: causes senescence
- ACC deaminase used to inhibit ethylene
in what 3 main ways does PGPR suppress plant disease?
- direct antibiosis
- competition for iron
- induction of systemic resistance (ISR)
what is direct antibiosis?
cant grow fungi near bacterial colony as compounds toxic to fungus
how may iron competition reduce plant growth?
- rhizobacteria may steal iron from other fungi and outcompete
- fluorescent siderophores produced that bind with high affinity to iron
what does ISR do?
- protects plant from pathogen and herbivores
- can change immune status of host plant
in Arabidopsis what can PGPR induce?
resistance against pests and disease
when leaves are infected how do caterpillars perform?
worse and grow slower therefore plant is better protected
when testing for leaf spot disease what was found for the P.fluorescens infected plant?
spreads less
why must the plant have lots of defence mechanisms?
lots of mechanisms used to cause disease and have to fight off lots of different attackers
what is the protection like for plants grown in soil enriched with PGPR?
more protected
induced defence in plants is costly how is this shown in Arabidopsis?
may be resistant but growth is stunted as investing lots into defence mechanisms
what is immune priming? (4)
- immunological memory
- intermediate stage if defence allowing bacteria to prime
- allows them to develop a stronger immune response after pathogen attack
- induced resistance
list the 4 main signalling pathways controlling P.fluorescens in induced defence priming
MYB72
BGL42
MYC2
ABA1
what is/does it do: MYB72?
transcription factor in roots tricking plants into thinking they are iron deprived so exudes other root exudates
what is/does it do: BGL42?
second to act
B-glucosidase hydrolytic enzyme that can cleave glucose and activate secondary metabolites
what is/does it do: MYC2?
- in leaves priming depends on this transcription factor
- jasmonic acid defence genes activated
what does jasmonic acid gene activate?
inducible defences against herbivores and necrotrophic fungi
what is/does it do: ABA1?
primes cell wall defence
- better defence if grown in presence of P.fluorescens
involving P.putida what happens when SerPIN proteins accumulate in leaves ?
leaves less nutritionally beneficial to caterpillars so eaten by less
briefly what is the step by step for priming by root colonisation of P.putida on maize? (4)
- bacteria activates signal priming shoot for antiherbivore defences under jasmonic acid control
- SerPIN proteins accumulate
- sensitised leading to augmented expression
- emit airborne compounds/inducible volatiles
what do inducible volatiles do?
immobilise other organisms by attracting other insects to attack caterpillars
what do signals plants use to obtain beneficial bacteria use?
root exudation chemistry
- secrete complex metabolites
what is DIMBOA? (4)
- secondary metabolite
- high levels in young seedlings but reduces over time
- selective activity
- can kill off pathogens
when growing the plant at increasing concentrations of DIMBOA what was found?
- P.putida could still grow as very tolerant
what does DIMBOA induce in p.putida?
chemotaxis
when carrying out a DIMBOA induced transcriptome what was discovered?
lots of genes upregulated
- most involved in breakdown of aromatic compounds including DIMBOA
what is chemotaxis?
microbe behavioural response to chemical stimulus and can move towards or away from it
what kind of signal can DIMBOA act as for bacteria?
recruitment
could activate cells to be attracted to the source
what kind of compound is DIMBOA?
BX
what could the created BX1 mutant not do?
produce BX compounds such as DIMBOA
what was found when grew wild type and BX1 mutant on non sterile agar plate ?
lower fluorescence in BX1 mutant so less able to sustain growth by P.putida
what did the BX6 mutation do?
DIBOA-> DIMBOA obstructed
so more DIBOA
what are crown roots?
take up nutrients and act as storage organs
- more DIBOA and DIMBOA in these roots
what are bacterial species referred to as?
operational taxonomic units
what are the 4 main stages for microbial community analysis by sequencing rRNA genes?
- DNA extracted from microbes in rhizosphere
- primers amplify variable internal transcribed spacer ITS2 between conserved rRNA genes
- PCR to study taxonomy
- sequence
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?
strong
more BX in crown roots
- less intense impact on community structure
what were the predicted breakdown products from DIBOA and DIMBOA?
(M)BOA
what did the follow on study by Hu et al do/find? ()
- 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
