Hormones 02 Flashcards
ABA controls
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
How is ABA upregulated in seed germination?
Accumulation/regulation of production by upstream metabolic processes (directly correlates with environmental stress)
ABA biosynthetic pathway
Initially derives from terpenoids => carotenoids
Like CK, GA and BR
Stress responsive geness induced by ABA include
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)
ABA perception
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)
Stomatal closure
ABA causes rapid influx of Ca2+ => activation of further kinases => activate other ion channels (e.g. potassium)
Ethylene
Gas! => diffusion
Ethylene controls
fruit ripening
Leaf and petal senescence
Cell division & elongation
Sex determination in some plants
Root growth
Stress responses (pathogens, wounding, flooding => hypoxia)
Ethylene discovery
Candles => plants tend to grow in direction of plant
And even before: fruit ripening through ethylene in smoke
Fruits that are sensitive to ethylene
Climacteric
Ethylene biosynthesis
From methionine (ACC is precursor)
AdoMet => ACS (ACC Synthase) => ACC (1-amino-cyclopropanecarboxylate) => ACO (ACC oxidase) => Ethylene
What is the triple response?
Response to wounding/mechanical stress => ethylene production
• reduced elongation
• hypocotyl swelling
• apical hook exaggeration
Ethylene perception
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
Salicylic Acid (SA)
=> aspirin from salix alba
SA regulates
response to stress (pathogens, UV)
development
mostly through gene expression
SA synthesis and function
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
Perception of SA general
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
Molecular perception of SA
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
Jasmonic Acid regulates
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
Most active form of JA
JA-Ile conjugated form
MeJA is more potent volatile (between plants/diff plant parts most efficient)
Jasmonate discovery
Smell of jasmine flowers
Mimic pathogen => increase of JA
JA Biosynthesis
First step in plastid => originates from lipids in plastid membrane
Fibal step in peroxisome => precursor into JA
Conjugation to JA-Ile by enzyme (JAR)
Which is the limiting step in JA production?
Conjugation to JA-Ile
JA-Ile perception and gene expression
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
What is special about Auxin and JA receptors?
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
By which other hormones can the JAZ repressor be regulated?
GA (DELLA) and SA (NPR)
What is the ‘antagonistic’ hormone to JA?
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
What immune responses are induced by JA and SA?
JA: induced systemic resistance (herbivory) & local => from root to shoot
SA: systemic acquired response (& local)
Strigolactones
Only recently recognized
Best studied: strigol
Biosynthesis
From carotenoids like ABA
SL regulate…
seemingly unrelated events
inhibit shoot branching
promote associations with arbuscular mycorrhizal fungi
promote germination of parasitic striga plant
SL perception
Similar to Auxin, but accessory protein for perception
Which four hormones have a similar perception pathway?
Auxin
GA
JA
SL
Endogenous peptides/secreted signaling peptides
regulate almost everything
Large number of diff peptides
Locally (autocrine), long distance signals (paracrine)
Systemic signaling
Receptors and functions mostly unknown
Cryptic peptides
Cleave product of proteins have signaling function
Which classes of plant peptide hormones exist?
• functional-precursor derived peptides (cryptic)
• post-translationally modified
• cystein rich (disulfide bonds => 3D structure)
• linear unmodified peptides
Peptide hormone perception
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
