Hormones 02

Question 1

ABA controls

Answer 1

dessication tolerance of seeds
inhibits germination and promotes dormancy
transcriptional responses in development and to biotic stresses through gene expression
=> and physiological responses like closure of stomates

Question 2

How is ABA upregulated in seed germination?

Answer 2

Accumulation/regulation of production by upstream metabolic processes (directly correlates with environmental stress)

Question 3

ABA biosynthetic pathway

Answer 3

Initially derives from terpenoids => carotenoids
Like CK, GA and BR

Question 4

Stress responsive geness induced by ABA include

Answer 4

Osmoprotectants
Membrane and protein stabilization (LEA)
Oxidative stress responses (peroxidase, superoxide dismutase)
Movement of water and ions => aquaporins and ion channels (stomatal closure => influx of ions)

Question 5

ABA perception

Answer 5

negative regulation of negative regulation but diff mechanism than proteasome

SnRK2 kinase activity inhibited by PP2C phosphatase => complex formation with phosphatase upon ABA perception by PYR/PYL/RCAR receptors => conf. change => inactivation of phosphatase => SnRK2 activation => phosphorylates TF (and ion channels)

Question 6

Stomatal closure

Answer 6

ABA causes rapid influx of Ca2+ => activation of further kinases => activate other ion channels (e.g. potassium)

Question 7

Ethylene

Answer 7

Gas! => diffusion

Question 8

Ethylene controls

Answer 8

fruit ripening
Leaf and petal senescence
Cell division & elongation
Sex determination in some plants
Root growth
Stress responses (pathogens, wounding, flooding => hypoxia)

Question 9

Ethylene discovery

Answer 9

Candles => plants tend to grow in direction of plant
And even before: fruit ripening through ethylene in smoke

Question 10

Fruits that are sensitive to ethylene

Answer 10

Climacteric

Question 11

Ethylene biosynthesis

Answer 11

From methionine (ACC is precursor)
AdoMet => ACS (ACC Synthase) => ACC (1-amino-cyclopropanecarboxylate) => ACO (ACC oxidase) => Ethylene

Question 12

What is the triple response?

Answer 12

Response to wounding/mechanical stress => ethylene production

• reduced elongation
• hypocotyl swelling
• apical hook exaggeration

Question 13

Ethylene perception

Answer 13

ETR1 receptor (ethylene responsive 1)
binds ethylene
membrane localized (ER)
Histidine kinase => similarity with cytokinin receptors

bound to RAF like kinase => active => phosphorylates other protein in ER membrane EIN2 (if not present, the plant cannot respond to ethylene) => bound to F-box => EIN2 mostly degraded
& in nucleus: negative regulation of transcription factors

inactivation of RAF-like kinase upon Ethylene binding to ETR receptor => does not phosphorylate EIN2 => EIN2 accumulates => protease cleaves C-terminal domain of EIN2 => moves to nucleus => deactivation of F-box in nucleus by EIN2 allows activation of TFs

Question 14

Salicylic Acid (SA)

Answer 14

=> aspirin from salix alba

Question 15

SA regulates

Answer 15

response to stress (pathogens, UV)
development

mostly through gene expression

Question 16

SA synthesis and function

Answer 16

Enzymes that directly control SA (Isochorismate synthase) are higher expressed upon pathogen infection
=> occurs in chloroplasts => produce Isochorismate 1 (precusor)
=> exported into cytosol => production of SA

Second pathway (10%) involves phenylalanine

SA accumulation leads to pathogenesis related (PR) genes being transcribed

Question 17

Perception of SA general

Answer 17

local and systemic
both at membrane and intracellular receptors

SA accumulation upon infection => production of mobile signal (through xylem => accumulation of SA in other parts of plant => systemic acquired resistance

Question 18

Molecular perception of SA

Answer 18

NPR proteins
equilibrium of monomers and polymers in cytosol
=> only monomers can move into
nucleus => is TF

NPR itself is SA receptor: binds directly and equilibrium is then shifted towards monomeric form

Question 19

Jasmonic Acid regulates

Answer 19

Response to necrotrophic pathogens
Response to wounding
Induction anti-herbivory responses
Production of herbivore-induced volatiles to prime other tissues/plants and attract predatory insects
reproductive development
trichome development

Question 20

Most active form of JA

Answer 20

JA-Ile conjugated form
MeJA is more potent volatile (between plants/diff plant parts most efficient)

Question 21

Jasmonate discovery

Answer 21

Smell of jasmine flowers

Mimic pathogen => increase of JA

Question 22

JA Biosynthesis

Answer 22

First step in plastid => originates from lipids in plastid membrane
Fibal step in peroxisome => precursor into JA
Conjugation to JA-Ile by enzyme (JAR)

Question 23

Which is the limiting step in JA production?

Answer 23

Conjugation to JA-Ile

Question 24

JA-Ile perception and gene expression

Answer 24

Exactly like Auxin
=> receptor COI1 is associated with proteasome, upon binding of JA conformational change that increases affinity for neg regulator of TF => degraded & gene transcription can take place

Question 25

What is special about Auxin and JA receptors?

Answer 25

Very high structural similarity btw TIR1 and COI1
Only diff is exact binding domain for hormone
Both mostly consist of LRRs

=> gene duplication and diff evolution from there => might originate from same receptor

Question 26

By which other hormones can the JAZ repressor be regulated?

Answer 26

GA (DELLA) and SA (NPR)

Question 27

What is the ‘antagonistic’ hormone to JA?

Answer 27

SA => either one or the other produced, if one than response to other is inhibited

=> JA for necrotrophic patogens
=> SA for biotrophic pathogens

=> ethylene in contrast is produced at same time as JA mostly

Question 28

What immune responses are induced by JA and SA?

Answer 28

JA: induced systemic resistance (herbivory) & local => from root to shoot
SA: systemic acquired response (& local)

Question 29

Strigolactones

Answer 29

Only recently recognized
Best studied: strigol

Question 30

Biosynthesis

Answer 30

From carotenoids like ABA

Question 31

SL regulate…

Answer 31

seemingly unrelated events

inhibit shoot branching
promote associations with arbuscular mycorrhizal fungi
promote germination of parasitic striga plant

Question 32

SL perception

Answer 32

Similar to Auxin, but accessory protein for perception

Question 33

Which four hormones have a similar perception pathway?

Answer 33

Auxin
GA
JA
SL

Question 34

Endogenous peptides/secreted signaling peptides

Answer 34

regulate almost everything
Large number of diff peptides
Locally (autocrine), long distance signals (paracrine)
Systemic signaling
Receptors and functions mostly unknown

Question 35

Cryptic peptides

Answer 35

Cleave product of proteins have signaling function

Question 36

Which classes of plant peptide hormones exist?

Answer 36

• functional-precursor derived peptides (cryptic)
• post-translationally modified
• cystein rich (disulfide bonds => 3D structure)
• linear unmodified peptides

Question 37

Peptide hormone perception

Answer 37

Trans-membrane proteins
• recepror-like proteins (without kinase domain) => trimey complex
• receptor kinases => recquire co-receptor
=> ligand induced proximity/complex (molecular glue)

Extracellular domain consists of LLRs