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Growth regulators Auxins Cytokinins Gibberellins Abscisic acid Ethylene Brassinosteroids Strigolactones All are small organics: made in one part, affect another part
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Auxin Action Two models: Acid growth: IAA starts H+ pumping that loosens cell wall Gene activation
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Auxin Action IAA induces PM H+ pump with 10' lag Acid- growth: IAA-induced pH drop activates expansins & glucanases Lag may represent time needed to move H+ pump to PM Also have SAUR genes expressed w/in 10'! Some are light-regulated: induced in cotyledons & repressed in hypocotyls Controlled by PIFs
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Auxin Action Phototropism is due to more elongation on shaded side due to lateral IAA redistribution IAA export blockers stop phototropism PIN1 goes away in cells on light side & PIN3 on cell sides takes over IAA moves sideways Lower pH on shaded side enhances IAA uptake
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Auxin Action Gravitropism Shoots bend up, Roots bend down Both effects are due to IAA redistribution to lower side! [IAA] stimulates shoots & inhibits roots!
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Apical dominance Auxin inhibits lateral bud formation decapitate plant and lateral buds develop apply IAA to cut tip & lateral buds do not develop
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Apical dominance Auxin induces lateral & adventitious roots Promotes cell division at initiation site Promotes cell elongation & viability as root grows
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Auxin signaling Used "auxin-resistant" mutants to find genes involved in auxin signaling Many are involved in selective protein degradation!
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Auxin signaling Auxin receptors eg TIR1 are E3 ubiquitin ligases! Upon binding auxin they activate complexes targeting AUX/IAA proteins for degradation! AUX/IAA inhibit ARF transcription factors, so this turns on "early genes"
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Auxin signaling ABP1 is a different IAA receptor localized in ER Activates PM H+ pump by sending it to PM & keeping it there Does not affect gene expression!
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Cytokinins Discovered as factors which induce cultured cells to divide Haberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates division Miller… Skoog (1955): degraded DNA stimulates division! Kinetin was the breakdown product Derived from adenine Requires auxin to stimulate division
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Cytokinins Requires auxin to stimulate division Kinetin/auxin determines tissue formed (original fig)
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Cytokinins Miller& Letham (1961) ± simultaneously found zeatin Later found in many spp including coconut milk Trans form is more active, but both exist (& work) Many other natural & synthetics have been identified
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Cytokinins Many other natural & synthetics have been identified Like auxins, many are bound to sugars or nucleotides
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Cytokinins Many other natural & synthetics have been identified Like auxins, many are bound to sugars or nucleotides Inactive, but easily converted
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Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem
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Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem Therefore have inverse gradient with IAA
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Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem Therefore have inverse gradient with IAA Why IAA/CK affects development
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Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem Therefore have inverse gradient with IAA Why IAA/CK affects development Rapidly metabolized by sink
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Cytokinin Effects Regulate cell division Need mutants defective in CK metabolism or signaling to detect this in vivo
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Cytokinin Effects Regulate cell division Need mutants defective in CK metabolism or signaling to detect this in vivo SAM & plants are smaller when [CK]
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Cytokinin Effects SAM & plants are smaller when [CK] Roots are longer!
![Cytokinin Effects SAM & plants are smaller when [CK] Roots are longer!](http://slideplayer.com./slide/13396876/80/images/22/Cytokinin+Effects+SAM+%26+plants+are+smaller+when+%5BCK%5D+Roots+are+longer%21.jpg "Cytokinin Effects SAM & plants are smaller when [CK] Roots are longer!")
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Cytokinin Effects Usually roots have too much CK: inhibits division! Cytokinins mainly root & shoot meristems
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Cytokinin Effects Cytokinins mainly root & shoot meristems Control G1-> S & G2-> M transition
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Cytokinin Effects Promote lateral bud growth
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Cytokinin Effects Promote lateral bud growth Delay leaf senescence
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Cytokinin Effects Promote lateral bud growth Delay leaf senescence Promote cp development, even in dark
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Cytokinin Receptors Receptors were identified by mutation Resemble bacterial 2-component signaling systems
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Cytokinin Action 1.Cytokinin binds receptor's extracellular domain
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Cytokinin Action 1.Cytokinin binds receptor's extracellular domain 2. Activated protein kinases His kinase & receiver domains
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Cytokinin Action 1.Cytokinin binds receptor's extracellular domain 2. Activated protein kinases His kinase & receiver domains 3. Receiver kinases His-P transfer relay protein (AHP)
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Cytokinin Action 1.Cytokinin binds receptor's extracellular domain 2. Activated protein kinases His kinase & receiver domains 3. Receiver kinases His-P transfer relay protein (AHP) 4. AHP-P enters nucleus & kinases ARR response regulators
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Cytokinin Action 4. AHP-P enters nucleus & kinases ARR response regulators 5. Type B ARR induce type A
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Cytokinin Action 4. AHP-P enters nucleus & kinases ARR response regulators 5. Type B ARR induce type A 6. Type A create cytokinin responses
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Cytokinin Action 4. AHP-P enters nucleus & kinases ARR response regulators 5. Type B ARR induce type A 6. Type A create cytokinin responses 7. Most other effectors are unknown but D cyclins is one effect.
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Auxin & other growth regulators
Some "late genes" synthesize ethylene (normally a wounding response): how 2,4-D kills? Auxin/cytokinin determines whether callus forms roots or shoots Auxin induces Gibberellins
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Gibberellins Discovered by studying "foolish seedling" disease in rice Hori (1898): caused by a fungus
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Gibberellins Discovered by studying "foolish seedling" disease in rice Hori (1898): caused by a fungus Sawada (1912): growth is caused by fungal stimulus
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Gibberellins Discovered by studying "foolish seedling" disease in rice Hori (1898): caused by a fungus Sawada (1912): growth is caused by fungal stimulus Kurosawa (1926): fungal filtrate causes these effects
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Gibberellins Discovered by studying "foolish seedling" disease in rice Kurosawa (1926): fungal filtrate causes these effects Yabuta (1935): purified gibberellins from filtrates of Gibberella fujikuroi cultures
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Gibberellins Discovered by studying "foolish seedling" disease in rice Kurosawa (1926): fungal filtrate causes these effects Yabuta (1935): purified gibberellins from filtrates of Gibberella fujikuroi cultures Discovered in plants in 1950s
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Gibberellins Discovered in plants in 1950s "rescued" some dwarf corn & pea mutants
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Gibberellins Discovered in plants in 1950s "rescued" some dwarf corn & pea mutants Made rosette plants bolt
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Gibberellins Discovered in plants in 1950s "rescued" some dwarf corn & pea mutants Made rosette plants bolt Trigger adulthood in ivy & conifers
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Gibberellins "rescued" some dwarf corn & pea mutants Made rosette plants bolt Trigger adulthood in ivy & conifers Induce growth of seedless fruit
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Gibberellins "rescued" some dwarf corn & pea mutants Made rosette plants bolt Trigger adulthood in ivy & conifers Induce growth of seedless fruit Promote seed germination
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Gibberellins "rescued" some dwarf corn & pea mutants Made rosette plants bolt Trigger adulthood in ivy & conifers Induce growth of seedless fruit Promote seed germination Inhibitors shorten stems: prevent lodging
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Gibberellins "rescued" some dwarf corn & pea mutants Made rosette plants bolt Trigger adulthood in ivy & conifers Induce growth of seedless fruit Promote seed germination Inhibitors shorten stems: prevent lodging >136 gibberellins (based on structure)!
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Gibberellins >136 gibberellins (based on structure)! Most plants have >10
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Gibberellins >136 gibberellins (based on structure)! Most plants have >10 Activity varies dramatically!
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Gibberellins >136 gibberellins (based on structure)! Most plants have >10 Activity varies dramatically! Most are precursors or degradation products
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Gibberellins >136 gibberellins (based on structure)! Most plants have >10 Activity varies dramatically! Most are precursors or degradation products GAs 1, 3 & 4 are most bioactive
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Gibberellin signaling
Used mutants to learn about GA signaling
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Gibberellin signaling
Used mutants to learn about GA signaling Many are involved in GA synthesis
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Gibberellin signaling
Used mutants to learn about GA signaling Many are involved in GA synthesis Varies during development
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Gibberellin signaling
Used mutants to learn about GA signaling Many are involved in GA synthesis Varies during development Others hit GA signaling Gid = GA insensitive
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Gibberellin signaling
Used mutants to learn about GA signaling Many are involved in GA synthesis Varies during development Others hit GA signaling Gid = GA insensitive encode GA receptors
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Gibberellin signaling
Used mutants to learn about GA signaling Many are involved in GA synthesis Varies during development Others hit GA signaling Gid = GA insensitive encode GA receptors Sly = E3 receptors 58
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Gibberellin signaling
Used mutants to learn about GA signaling Many are involved in GA synthesis Varies during development Others hit GA signaling Gid = GA insensitive encode GA receptors Sly = E3 receptors DELLA (eg rga) = repressors of GA signaling
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Gibberellins GAs 1, 3 & 4 are most bioactive Act by triggering degradation of DELLA repressors
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Gibberellins GAs 1, 3 & 4 are most bioactive Made at many locations in plant Act by triggering degradation of DELLA repressors w/o GA DELLA binds & blocks activator (GRAS)
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Gibberellins Act by triggering degradation of DELLA repressors w/o GA DELLA binds & blocks activator bioactive GA binds GID1; GA-GID1 binds DELLA & marks for destruction
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Gibberellins Act by triggering degradation of DELLA repressors w/o GA DELLA binds & blocks activator bioactive GA binds GID1; GA-GID1 binds DELLA & marks for destruction GA early genes are transcribed, start GA responses
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