Prepare a 10’talk for Friday Feb 27 on plant defense responses or describe interactions between plants & pathogens or symbionts
Plant defense responses
• Hypersensitive response
• Systemic acquired resistance
• Innate immunity
• Phytoalexin synthesis
• Defensins and other proteins
• Oxidative burst
Some possible pathogens
• Agrobacterium tumefaciens
• Agrobacterium rhizogenes
• Pseudomonas syringeae
• Pseudomonas aeruginosa
• Viroids
• DNA viruses
• RNA viruses
• Fungi
• Oomycetes
Some possible symbionts
• N-fixing bacteria
• N-fixing cyanobacteria
• Endomycorrhizae
• Ectomycorrhizae

1.Auxins
2.Cytokinins
3.Gibberellins
4.Abscisic Acid
5.Ethylene
6.Brassinoteroids
7.Jasmonic Acid
8.Salicylic Acid
9.Strigolactones
10.Nitric Oxide
11.Sugars
Growth regulators

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"
Some early genes turn on
'late genes" needed for development

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!

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

Cytokinins
Discovered as factors which induce cultured cells to divide
Haberlandt (1913): phloem chemical stimulates division

Cytokinins
Discovered as factors which induce cultured cells to divide
Haberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates division

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!

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

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

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
Requires auxin to stimulate division
Kinetin/auxin determines tissue formed
Inspired search for natural cytokinins
Miller& Letham (1961) ± simultaneously found zeatin in corn
Kinetin transZeatin

Cytokinins
Miller& Letham (1961) ± simultaneously found zeatin
Later found in many spp including coconut milk
Kinetin transZeatin

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

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

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

Discovered in plants in 1950s
Gibberellins
• "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

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