VL 37 (Markus Grebe) Flashcards
General Scheme for Plant Signal Transduction
Signal Perception Can Occur at Different Subcellular Locations
Plasma membrane
* BRI: bind extracellular LRR-receptor domain; cytoplasmic kinase domain; recycled, degraded in endosomes
* PHOT1/2 (Phototropin): blue light receptor
* Msc5: mech. stimuli receptor
* GTG1/2: abscisic acid receptor
Chloroplast
* Msc5: mech. stimuli receptor
ER
* Cytokinin
* Ethylene
Nucleus
* TIR1: IAA receptor
* COI1: Jasmonate receptor
* GID1: Gibberelin receptor
Cytosol
* PYR: abscisic acid receptor
Auxin
- hormone
- neg. charge → no transport over membranes
Auxin Transport and Subcellular Compartmentalization – Modulate the Concentration of Active Auxin:
- deprotonated IAA + H+ → influx-carrier AUX1/LAX → into cell
- PIN: no ATPase activate; known to associate complexes; indicate direction of Auxin flow
- ABCB: ATP-driven; IAA anion efflux
➔ directed Auxin transport
→ contributes to tissue polarity - ER: Auxin-like proteins (PILS); APB1: binds Auxin
Auxin Signal Transduction
- Low Auxin → repressor proteins bind ARF TF → shut-off auxin response
- Auxin arrives → repressor proteins removed/degraded → switched-on expression
Reminder: SCF Complexes and Protein Degradation
Transcriptional Activation of the Auxin Response Upon Depression:
- SCFTIR1 SU of E3 Ub-ligase SCF complex
- SCFTIR1 + Aux/IAAs bind together as co-receptors auxin
→AUX/IAA repressor ubiquitination, degradation via 26S - TIR1 = Transport Inhibitor Resistant 1
- ARF TF activated → dimerize → gene expression
SCFTIR1 and AUX/IAAs form a co-receptor complex:
- Auxin binds between repressor TIR-box protein
- →poly-Ub
- →AUX/IAA degradation
Several Plant Hormone Receptors are components of SCF Ub-complexes:
➔ GA: shoot elongation; seet germination
Inactivation of BIN2 repressor kinase:
- found in cabbage, cauliflower (first isolated from pollen)
- BR-binding to BRI1 → BRI-BAK1 heterodimers + phosphorylation
- BR-signaling kinase (BSK) is phosphorylated
- BSK activates BSU1 (phosphatase) → BIN2 dephosphorylation → degradation → BES1, BZR1 not longer phosphorylated → active
- BR absence → BIN2 active (nucleus) → BES1, BZR1 phosphorylation → degradation
Repressor Retargeting as another Example of Signal Transduction by repressor inactivation:
- dark: COP1 represses HY5 TF + light-regulated genes involved in red light (phytochrome), blue light (cryptochrome) signaling
- Modification of subcellular COP1 repressor (action regulated) localization
- COP1 is light-dependent
Kinase and Phosphatase activities regulate Abscisic Acid (ABA) Signal Transduction:
- hormone
- function: osmotic regulation; growth inhibtion; stomatal closure; seed dries out, stored → survive → GA to germinate
- A) receptor binds protein phosphatase (PP2C) → active →
dephosphorylates SnRK2 → inactivated → signaling shut off - B) ABA binds receptor → dissociates PP2C → PP2C inactivated
→ kinase active → autophosphorylation → phosphorylates bZIP, other S
Multistep Versions of Bacterial Two-Component Systems in Plant
- Input domain: Cytokinin binds; ER located to cytosol
- →hormones stimulating cell division
- autophosphorlated (His kinase domain) transmitter domain
- P transferred to receiver domain
- Hpt domain: his phosphotransfer; accepts P from receiver
domain; move from ER → nucleus - Transcriptional regulators → phosphorylated → switch on
gene exptression
Cross Regulation – Mutual Regulation of Different Signaling Pathways:
Primary
* Positive: two input pathways regulate shared protein(s)→same response effect
* Negative: two input pathways converge on shared protein(s); pathway1 inhibits pathway2
Secondary
* Positive: two input pathways regulate separate responses; one pathway enhances input
levels/perception of other pathway
* Negative: (same as in positive); one pathway enhances represses levels/perception of other
pathway
Tertiary
* Positive: response of one of pathway promotes response of other pathway
* Negative: response of one of pathway inhibits response of other pathway
Structure of barley grain and functions of tissues during germination:
- GA synthesized by embryo → released into starchy endosperm via scutellum
- GA diffuse to aleurone layer
- Aleurone layer cells synthesize, secrete alpha-amylase (+ hydrolases) into endosperm
- Starch, macromolecules degradation
- Endosperm solutes absorbed by scutellum, transported to growing embryo
Induction of alpha-amylase synthesis in barley aleurone layers by GA:
