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B3.0 > Arbuscular Mycorrhizal Symbiosis > Flashcards

Arbuscular Mycorrhizal Symbiosis Flashcards

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1
Q

Structure

A

1.
2.
3.

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2
Q

symbiosis

A

the living together of unlike organisms

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3
Q

describe AMS

A

mutualistic plant-microbe interactions based on resource exchange

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4
Q

RNS

A
  • root nodule symbiosis
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5
Q

mycorrhizal symbiosis

A
  • 100% Pi
  • 40% N
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6
Q

AM fungal mycelia

A
  • improves plant mineral acquisition (nutrient status)
  • mycorrhizosphere
  • can functionally replace lateral roots to restore biomass (ltrl)
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7
Q

mycorrhizopshere

A
  • mycocosm
  • maximises nutrient uptake
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8
Q

zone of depletion

A
  • fungus can solubilise organic-bound
    • phytic-acid solubilising bacteria
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9
Q

arbuscules

A

uptake + root delivery

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10
Q

AMS benefits

A

i) bio-fertilisation (P, N, water)
ii) bio-protection (abiotic stresses)
iii) biostabilisation (soil and global cycling; C uptake and locking)

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11
Q

arbuscular endomycorrhizal associations

A
  • all plant lineages (200k sp.)
  • Mucoromucota (0.3k, 72%)
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12
Q

ectomycorrhizae

A
  • shrubs, trees (6k)
  • Basidio, Asco (20k, 2%)
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13
Q

orchid mycorrhizae

A
  • orchids (20-35k)
  • Basidiomycota (25k, 10%)
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14
Q

ericoid mycorrhizae

A
  • Ericaceae (4k)
  • Ascomycota (0.15k, 1.5%)
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15
Q

AMF features

A

i) obligate biotrophs
ii) fatty acid auxotrophs
iii) lack PCWDEs
iv) multinucleate spores
v) asexual
vi) 570Myo monophyly (subphylum: Glomeromycotina)

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16
Q

obligate biography

A
  • axenic culture
  • requires living host
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17
Q

fatty acid auxotrophs

A

lack fatty acid synthase

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18
Q

PCWDEs

A
  • plant cell wall degrading enzymes
  • cannot generate organic C
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19
Q

multinucleate spores

A
  • homo + heterokaryon strains
  • not genetically tractable
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20
Q

asexual AMF

A
  • coenocytic hyphae (4-6micrometer diameter)
  • anastomosis
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21
Q

model AMF

A
  • Rhizophagus irregularis DAOM 197198
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22
Q

AM symbiosis facilitated terrestrialisation

A

1) fossil records
2) broad distribution (e.g. early branching embryo-bytes)
3) molecular data (genome sequencing)

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23
Q

fossil records

A
  • ~407Mya: early Devonian Rhynie Chert
  • Aglaophyton major
  • rootless early embryophytes (bryophytic)
  • endophytic associations
  • “arbuscular” structures when compares to Z. mays
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24
Q

Z. mays

A

colonised by Gloms mosseae

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25
broad distribution
- ~85% of Cambridge Botanical Gardens (ink staining) - incl. ~460Mya (bryophytes); terrestrialisation - secondary loss in some families (Brassicaceae)
26
molecular data
- mining 'omics - Charales: "symbiotic toolkit"
27
Charales
- advanced Charophytes + ancestors - green algae
28
AMF Life Cycle
- pre-symbiotic dialogue: spores germinate in PSR-permissive rhizosphere - hyphopodia - intercellular hyphae - intracellular arbuscles
29
SL, flavonoid and karrakin-like production
- under PSR - fungal perception
30
karrakin-like
butenolide smoke constituent
31
What happens upon fungal perception of SL
- sporulation - branching
32
SL
- e.g. 5-DS
33
5-DS
- 5-deoxystrigol - fungal branching factor
34
striglocatone biosynthesis
- PSR - regulated by NSP1/2
35
NSP1/2
- GRAS TFs - PSR genes - heterodimerise for induction
36
nsp1/nsp2
- barley - SL-biosynthesis-defective - decreased total + arbuscule colonisation (%)
37
NSP1/2oe
- high strigoractone
38
NSP2oe
- high strigolactone even under high Pi
39
PDR1
- pleiotropic drug resistance 1 - SL transporter -> rhizosphere
40
fungal Myc factors - the basics
- chitinaceous - LCOs, COs - fatty acid moieties - structurally similar to Nod factors - not as specific - N-glycosamine acetyl/methyl substitutions - non(sulphated) - produced by mutualists and pathogens
41
fungal Myc factors - the specifics
i) produced by GSEs ii) LysM RLKs cause Ca2+ spiking
42
GSEs
- germinated spore exudates
43
COs
- Ca2+ spiking - lateral root induction
44
LCOs
- Ca2+ spiking - lateral root induction - root-hair branching
45
Nuclear Ca2+ spiking
- evidence of Myc perception during pre-symbiotic phase = inoculating roots w/ M; spike!
46
barley, wheat, maize + LCOs
- non-inoculating - spike!
47
LCO-mediated Ca2+ signalling is underpinned by
- nutrient status - Mt: low Pi/N = permissive (esp. for colonisation) - -P-N = double permissive
48
Perception
- modular - NFRI/5 (co-receptor; DEAD-domain binds LCO) - LysM domain confers specificity - in Mt, Lj and Os
49
nfr1-1, nfr1-2
- decreased root colonisation (p<0.05) - no spiking (YC36 reporter) - no CSSP
50
CSSP
- common symbiosis signalling pathway - Mt, Lj - forward genetics: N-deficiency, non-Rhizobia mutants - conserved genetic programmes for both symbioses - legume mutants (~10) deficient @ early stage for both - mediates Myc factor perception - requires SYMRK, Pollux/Castor, CCaMK, Cyclops, Ca2+
51
pollux
- LCOs, CO4 not perceived
52
SMAX1
- non-permissive brake - -ve regulator of AM symbiosis (specific) - inhibits NFR1 expression
53
D14L
- D14-like - SMAX1 proteolytic degradation - binds to karrakin-like ligand by alpha/b hydrolase - necessary for recruitment
54
SMAX1 proteolytic degradation
- D14L, D3/MAX2 (Ub)
55
F2: smax1-1
- increased root length colonisation (%)
56
F3: smax1-1
- increased root length colonisation (%)
57
F3: smax1-1SMAX1-1
recapitulates wt
58
alpha-b hydrolase
- D14L karrikin R
59
d14l-1/2 barley
- decreased total + arbuscle mycorrhizal colonisation (%) §
60
PPA
- pre-penetration apparatus - activated by CSSP - cytoskeletal reprogramming
61
Describe PPA cytoskeletal reprogramming
- MTs + actin form tube -> contact site - guides fungus through tube: cell -> cell - remains apoplastic - never breaches host cytosol
62
Hyphopodium formation - the basics
- triggers PPA to guide fungal ingress
63
Hyphopodium formation - the specifics
i) nucleus -> hyphopodial contact site ii) VAMP72, EXO84b redirect secretion to build peri-hyphal membrane ahead of hyphal tip growth; proliferation iii) secretory vesicles, MVBs, ER + Golgi arrange around invading hyphae
64
VAMP72, EXO84B
- vSNAREs - exocyst complex
65
arbuscules
- surrounded by host-derived PAM
66
PAM
- peri-arbuscular membrane - huge SA for nutrient + signal exchange
67
arbuscule formation requires
- VAMP721s - SYP132 - EXO70i subunit - plant sp. Vapyrin
68
VAMP721s
- v-SNARE
69
SYP132
- t-SNARE
70
EXO70i subunit
- part of the EXOCYST complex - AM-specific
71
Pi + N exchange @ PAM
- PHT1 - HAI - AMT2
72
HAI
proton-ATPase
73
AMT2
- ammonium uptake transporter
74
symbiosis sp. Pi transporters
- Os, Ri: PT11 - GFP shows tight outline; intimate association
75
pt11-1
no phosphate uptake
76
fatty acids
- necessary for arbuscule development - STR1/2
77
STR1/2
- stunted arbuscules - PAM-localised ABCG transporters
78
str1/2
- no fine hyphal branches - non-functional - no Pi delivery
79
DELLA1
- GRAS TF - positive regulator of arbuscule formation - necessary - PSR - suppresses growth
80
DELLA general mechanism
- DELLA is bound to GID1 - GA preferentially binds to GID1 - 26SP DELLA degradation
81
GA3
inhibits arbuscule formation
82
della delta18
- dominant mutant - can't bind GID1 - stable DELLA1 - forms arbuscules w/GA3
83
della1/2
- no arbuscules
84
DELLA1 specific mechanism
- DELLA1 positively regulates RAM1 via Cyclops
85
RAM1
- Reduced Arbuscular Mycorrhiza 1 - GRAS TF - fatty acid biosynthesis + arbuscule development master regulator - ER
86
ram1-1
- no arbuscules - small, stunted?
87
MtRAM1oe
- PT4, EXO70i auto-activation - heat map
88
PT4
- AM-specific
89
AM symbiosis genes and PSR
- 87%
90
Give some PSR AM symbiotic genes
- EXO70i - Vapyrin - OsPHR1/2/3
91
OsPHR1/2/3
- FA biosynthesis - signalling - nutrient transport - PAM formation

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