Growth regulators Auxins Cytokinins Gibberellins Abscisic acid Ethylene Brassinosteroids Strigolactones All are small organics: made in one part, affect another part

Auxin Action Two models: Acid growth: IAA starts H+ pumping that loosens cell wall Gene activation

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

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

Auxin Action Gravitropism Shoots bend up, Roots bend down Both effects are due to IAA redistribution to lower side! [IAA] stimulates shoots & inhibits roots!

Apical dominance Auxin inhibits lateral bud formation decapitate plant and lateral buds develop apply IAA to cut tip & lateral buds do not develop

Apical dominance Auxin induces lateral & adventitious roots Promotes cell division at initiation site Promotes cell elongation & viability as root grows

Auxin signaling Used "auxin-resistant" mutants to find genes involved in auxin signaling Many are involved in selective protein degradation!

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"

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!

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

Cytokinins Requires auxin to stimulate division Kinetin/auxin determines tissue formed (original fig)

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

Cytokinins Many other natural & synthetics have been identified Like auxins, many are bound to sugars or nucleotides

Cytokinins Many other natural & synthetics have been identified Like auxins, many are bound to sugars or nucleotides Inactive, but easily converted

Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem

Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem Therefore have inverse gradient with IAA

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

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

Cytokinin Effects Regulate cell division Need mutants defective in CK metabolism or signaling to detect this in vivo

Cytokinin Effects Regulate cell division Need mutants defective in CK metabolism or signaling to detect this in vivo SAM & plants are smaller when [CK]

Cytokinin Effects SAM & plants are smaller when [CK] Roots are longer!

Cytokinin Effects Usually roots have too much CK: inhibits division! Cytokinins mainly act @ root & shoot meristems

Cytokinin Effects Cytokinins mainly act @ root & shoot meristems Control G1-> S & G2-> M transition

Cytokinin Effects Promote lateral bud growth

Cytokinin Effects Promote lateral bud growth Delay leaf senescence

Cytokinin Effects Promote lateral bud growth Delay leaf senescence Promote cp development, even in dark

Cytokinin Receptors Receptors were identified by mutation Resemble bacterial 2-component signaling systems

Cytokinin Action 1.Cytokinin binds receptor's extracellular domain

Cytokinin Action 1.Cytokinin binds receptor's extracellular domain 2. Activated protein kinases His kinase & receiver domains

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)

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

Cytokinin Action 4. AHP-P enters nucleus & kinases ARR response regulators 5. Type B ARR induce type A

Cytokinin Action 4. AHP-P enters nucleus & kinases ARR response regulators 5. Type B ARR induce type A 6. Type A create cytokinin responses

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.

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

Gibberellins Discovered by studying "foolish seedling" disease in rice Hori (1898): caused by a fungus

Gibberellins Discovered by studying "foolish seedling" disease in rice Hori (1898): caused by a fungus Sawada (1912): growth is caused by fungal stimulus

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

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

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

Gibberellins Discovered in plants in 1950s "rescued" some dwarf corn & pea mutants

Gibberellins Discovered in plants in 1950s "rescued" some dwarf corn & pea mutants Made rosette plants bolt

Gibberellins Discovered in plants in 1950s "rescued" some dwarf corn & pea mutants Made rosette plants bolt Trigger adulthood in ivy & conifers

Gibberellins "rescued" some dwarf corn & pea mutants Made rosette plants bolt Trigger adulthood in ivy & conifers Induce growth of seedless fruit

Gibberellins "rescued" some dwarf corn & pea mutants Made rosette plants bolt Trigger adulthood in ivy & conifers Induce growth of seedless fruit Promote seed germination

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

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)!

Gibberellins >136 gibberellins (based on structure)! Most plants have >10

Gibberellins >136 gibberellins (based on structure)! Most plants have >10 Activity varies dramatically!

Gibberellins >136 gibberellins (based on structure)! Most plants have >10 Activity varies dramatically! Most are precursors or degradation products

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

Gibberellin signaling Used mutants to learn about GA signaling

Gibberellin signaling Used mutants to learn about GA signaling Many are involved in GA synthesis

Gibberellin signaling Used mutants to learn about GA signaling Many are involved in GA synthesis Varies during development

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

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

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

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

Gibberellins GAs 1, 3 & 4 are most bioactive Act by triggering degradation of DELLA repressors

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)

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

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