Adapting to Phosphate Availability Flashcards
1
Q
Structure
A
1.
2.
3.
2
Q
Phosphorus - the basics
A
- 11th most abundant element in Earth’s crust
- 5th most abundant element in planta
- 2nd most common plant micronutrient
- essenital for the growth, reproduction and functioning of all life on Earth
3
Q
Phosphorus functions
A
1) energy donors (ATP, ADP, AMP)
2) phospholipids
3) nucleic acids
4) starch/sucrose synthese
5) protein modification
6) regulation of metabolic pathways (energy transfer/aa synthesis)
4
Q
phosphate depletion symptoms
A
- stunted growth
- chlorosis
- increased root: shoot
- low metabolism
- poor seed quality
- decreased nitrogen uptake
- leaf drop
- poor frost R (+ other abiotic stresses)
5
Q
plants need to […] phosphate, for […]
A
forage; below and above-ground growth
6
Q
Pi fertilisers
A
necessary since the Green Revolution
7
Q
Green Revolution
A
- crops bred under high phosphate
- coincidental pop increase
8
Q
phosphate rock
A
- mined since the GR
- “peak phosphate”: deposit depletion
9
Q
1800s
A
Liebig identifies phosphorus in crop yields
10
Q
1850s
A
US Guano Islands Act
11
Q
Phosphate sources - the basics
A
- 90% in 5 countries (domestic reserves)
- Europe relies on import
- SSA: prohibitively expensive
12
Q
Phosphate sources
A
- Morocco (38%)
- China (27%)
- SA (10%)
- US (8%)
- Jordan (6%)
13
Q
2008, 2022
A
- phosphorus fertiliser value ^
- > $500/tonne (5x^)
- international socio-political influence; unreliable fluctuations
14
Q
application
A
- ~80% P unassimilated, unused
- anionic orthophosphate
- inorganic Pi
- depends on soil pH
15
Q
acidic soils
A
Fe
16
Q
neutral
A
- Al
- most accessible; v few
17
Q
alkaline
A
- Ca
- inaccessible as phytic acid
18
Q
phytic acid
A
- inositol hexaphosphate (organically bound P)
- immobile; not labile
- insoluble
- 1-10micometre availability
- only taken up if next to roots
- inaccessible
19
Q
Pi uptake
A
- creates a nutrient depletion zone around the roots
- 31P-labelled soil slows uptake took
20
Q
P inputs
A
fertiliser + manure
21
Q
PUE
A
P yield/P inputs
22
Q
P surplus
A
P inputs - P yields
23
Q
P residual
A
- P surplus - P loss
- aka legacy P
24
Q
P loss
A
- leaching
- run-off
- erosion
25
minimise negative environmental impact
- eutrophication
- lake hypoxia
- sustainable Agriculture
26
Ideas
i) P recycling
ii) improve crop traits
iii) improve agricultural practices
iv) symbionts
27
global pattern of agronomic Pi imbalances
- surplus can arise due to high application/usage
- 29% global cropland area is deficient
28
PSR in shoots
i) higher recycling, mobilisation
ii) decreased photosynthesis
iii) increased sugar concentration
iv) anthocyanin accumulation
v) lipid remodelling
vi) growth retardation
29
PSR in the roots
- increased uptake, translocation
- changing RSA
- increase organic acid + acid phosphatase secretion
- changing metabolism
- lipid remodelling
- flavonoid + SL exudation (AMF interactions)
30
RSA
- root system architecture
- decreased gravitropism
- increased formation and elongation of lateral roots and root hairs
- aerenchyma
- clusters
- shallow: topsoil foraging
31
aerenchyma
- air spaces
- metabolically inexpensive growth
32
biochemical PSR - the basics
- root educate secretion to increase Pi availability
33
biochemical PSR - the specifics
i) organic acids
ii) EC acid phosphatases
iii) flavonoids + SLs
34
organic acids
- malate, citrate
- solubilise Fe/ Al-OH-bound P
35
EC acid phosphatases
solubilise organically bound P
36
flavonoids and SLs
- attract free living and symbiotic beneficial micro-organisms for P solubilisation
37
PHTs
- plant phosphate transports
- PHO84/PHT1
38
PHO84
- S. cerevisiae
- homologs in Neurospora crassa
39
PHT1
- Arabidopsis (9x)
- Group II
- AM specific
- large gene family
- M.t: localises -> PM (6x)
- O.s: 13x
- expressed in epidermis + central cylinder of root hair zone
- PHO84 heterologous complementation
- pht1: attenuated uptake
40
PHT1-5
- MFS
- PHSs
- requires H+-ATPase
- overlap + functional redundancy
41
MFS
Major Facilitator Superfamily
42
PHSs
- phosphate: H+ symporters
43
PHT1-5 transcriptional regulation
- induced in PSR
- RT-PCR
- GSP/GUS
- in situ hybridisation
44
PHT1-5 post-transcriptional regulation
- under PSR
- PHF1
45
PHF1
- phosphate transport traffic facilitator 1
- mediates PHT1 secretion from ER -> PM (mCherry)
- necessary
46
- Atphf
- impaired Pi uptake (not SO4[2-])
- PHT1-GFP remains ER-bound
47
Under normal conditions, PHT1
- phosphorylated @ Ser51; does not exit ER
- targeted to vacuole for degradation (concanamycin A)
- removed from PT by endosomes
48
concanamycin A
- potent V-ATPase inhibitor
- vacuolar alkalinisation: fragmentation
49
Under low Pi, PHT/F1
- stabilised @ PM by endoscopes
50
PHT2+4
chloroplasts
51
PHT4
- Golgi, plastid
52
PHT3
mitochondria
53
PHT5
- vacuolar
- tonoplastic
- mediates intracellular Pi homeostasis
- soil pH adaptation
- + VPE1
54
VAC-Pi
- ~95%
- 5-20mm
- 31P-NMR
55
CYT-Pi
- 60-80micromoles
56
VPE1
vacuolar Pi efflux transporter
57
pht5
- reverse genetics (T-DNA insertions)
- decreased VAC-PI (31P-MRS)
- sensitive to high Pi
- reduced root length, biomass
58
31P-MRS
differentiates VAC/CYT-Pi by chemical shift
59
COM1
- PHT5-wt complemented mutant
- VAC-Pi: restored
60
VPE
- screening for tonoplastic proteins (brightfield microscopy)
- proteomic identification (iTRAQ)
- GlpT homologue
61
GlpT
- glycerol-3-phosphate transporter
- E. coli
62
VPE complementation
- Pi transport activity in yeast and Xenopus oocytes
- G3P-independent
63
Osvpe1vp2
- increased Vac-Pi
- 31P-NMR
64
NMR
nuclear magnetic resonance
65
OsVPE1/2oe
- decreased VAC-Pi
- 31P-NMR
66
Under low Pi
- PHTI, VPE upregulation
67
Under sufficient Pi
- PHT1 degraded
- PHT5 -> vacuole
68
