Plant defense responses Hypersensitive response 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

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

Auxin First studied by Darwins! Showed that a "transmissible influence" made at tips caused bending lower down No tip, no curve!

Auxin 1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark Uneven amounts of "transmissible influence" makes bend 1926: Went showed that a chemical that diffused from tips into blocks caused growth If placed asymmetrically get bending due to asymmetrical growth Amount of bending depends on [auxin] 1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending

IAA IBA 4-CI-IAA PA Auxin 1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending IAA is the main auxin in vivo. Others include Indole-3-butyric acid (IBA), 4-Chloroindole-3-acetic acid and phenylacetic acid (PA) IAA IBA 4-CI-IAA PA

IAA Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work! Widely used in agriculture to promote growth (flowering, cuttings) as weed killers! Agent orange was 1:1 2,4-D and 2,4,5-T IAA

IAA Auxin weed killers! Agent orange was 1:1 2,4-D and 2,4,5-T 2,4,5-T was contaminated with dioxin, a carcinogen IAA

IAA Auxin weed killers! Agent orange was 1:1 2,4-D and 2,4,5-T 2,4,5-T was contaminated with dioxin, a carcinogen 2,4-D is still widely used: selectively kills dicots IAA

Auxin weed killers! 2,4-D is still widely used: selectively kills dicots Controls weeds in monocot crops (corn, rice, wheat) Mech unclear: may cause excess ethylene or ABA production. IAA

Auxin weed killers! 2,4-D is still widely used: selectively kills dicots Controls weeds in monocot crops (corn, rice, wheat) Mech unclear: may cause excess ethylene or ABA production. IAA

Auxin >90%of IAA is conjugated to sugars in vivo!

Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated!

Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated! Best way to measure [auxin] is bioassay!

Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated! Best way to measure [auxin] is bioassay! Critical concentration varies between tissues

Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated! Best way to measure [auxin] is bioassay! Critical concentration varies between tissues Roots are much more sensitive than leaves!

Auxin Critical concentration varies between tissues Roots are much more sensitive than leaves! Made in leaves & transported to roots so [IAA] decreases going down the plant Most cells are IAA sinks!

Auxin Synthesis Made in leaves & transported to roots so [IAA] decreases going down the plant Most is made from trp

Auxin Synthesis Most is made from trp Also made by trp-independent pathway: exits before trp

Auxin Synthesis Most is made from trp Also made by trp-independent pathway: exits before trp Path used varies between tissues

Auxin Synthesis Most is made from trp Also made by trp-independent pathway: exits before trp Path used varies between tissues No way to run out of IAA

Auxin Levels No way to run out of IAA! [IAA] depends on metabolism

Auxin Levels No way to run out of IAA! [IAA] depends on metabolism Most cells are IAA sinks!

Auxin Levels No way to run out of IAA! [IAA] depends on metabolism Most cells are IAA sinks! IAA is made at shoot apex & transported down: basipetal

Auxin Levels No way to run out of IAA! [IAA] depends on metabolism Most cells are IAA sinks! IAA is made at shoot apex & transported down: basipetal IAA transport therefore affects growth & development

Auxin Transport IAA transport therefore affects growth & development is polar and basipetal: New roots form at base of stem even if stored upside-down

Auxin Transport IAA transport therefore affects development: is polar and basipetal. New roots form at base of stem even if stored upside-down. Stem sections only move IAA basipetally

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- -

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- 2. In cell IAAH-> IAA- due to pH 7.2 -

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- 2. In cell IAAH-> IAA- due to pH 7.2, , draws more IAAH -

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- 2. In cell IAAH-> IAA- due to pH 7.2, draws more IAAH 3. IAA- is pumped out by PIN proteins in basal part of cell -

Chemiosmotic Auxin Transport Apoplastic IAAH diffuses into cell IAAH due to low pH AUX1 pumps in IAA- 2. In cell IAAH-> IAA- due to pH 7.2, draws more IAAH 3. IAA- is pumped out by PIN proteins in basal part of cell 4. In apoplast IAA- -> Cycle repeats

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux into block, no effect on uptake

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux into block, no effect on uptake Import blockers stop uptake

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux , no effect on uptake Import blockers stop uptake Both mess up development!

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux , no effect on uptake Import blockers stop uptake Both mess up development! Natural transport inhibitors have anti-cancer activity!

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Export blockers stop efflux , no effect on uptake Import blockers stop uptake Both mess up development! Natural transport inhibitors have anti-cancer activity! Genistein binds estrogen receptors

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Both mess up development! 2.AUX1 encodes an IAA-H+ symporter found at top of cell

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export Both mess up development! 2.AUX1 encodes an IAA-H+ symporter found at top of cell aux1 resemble plants treated with import blockers

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export 2.AUX1 encodes an IAA-H+ symporter found at top of cell aux1 resemble plants treated with import blockers 3. PINs encode IAA exporters found at cell base

Chemiosmotic Auxin Transport Supporting evidence Some chemicals specifically block import or export 2.AUX1 encodes an IAA-H+ symporter found at top of cell aux1 resemble plants treated with import blockers 3. PINs encode IAA exporters found at cell base pin1 resemble plants treated with export blockers

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

Auxin Action Two models: Acid growth: IAA starts H+ pumping that loosens cell wall Low pH is sufficient to cause elongation

Auxin Action Two models: Acid growth: IAA starts H+ pumping that loosens cell wall Low pH is sufficient to cause elongation H+ pump activators cause elongation

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

Auxin Action IAA activates cell elongation & transcription in targets

Auxin Action IAA activates cell elongation & transcription in targets Elongation has lag of 10'

Auxin Action IAA activates cell elongation & transcription in targets Elongation has lag of 10' IAA induces PM H+ pump with 10' lag

Auxin Action IAA induces PM H+ pump with 10' lag Acid- growth: IAA-induced pH drop activates expansins & glucanases

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

Active transport H+ pumps lower pH in lysosomes, stomach

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 Gnom mutants stop transport of PIN1 to PM = links GTP exchange factor & development

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'!

Auxin Action Acid- growth: IAA-induced pH drop activates expansins & glucanases Phototropism is due to more elongation on shaded side

Auxin Action Acid- growth: IAA-induced pH drop activates extensins & glucanases Phototropism is due to more elongation on shaded side due to lateral IAA redistribution

Auxin Action Acid- growth: IAA-induced pH drop activates extensins & glucanases Phototropism is due to more elongation on shaded side due to lateral IAA redistribution IAA export blockers stop phototropism

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

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

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!

Auxin Action Gravitropism Shoots bend up! Roots bend down!

Auxin Action Gravitropism Shoots bend up! Roots bend down! Both effects are due to IAA redistribution to lower side!

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

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

Apical dominance Auxin induces lateral & adventitious roots Promotes cell division at initiation site

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

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

Auxin signaling Used "auxin-resistant" mutants to find genes involved in auxin signaling Many are involved in selective protein degradation! Some auxin receptors, eg TIR1 are E3 ubiquitin ligases!

Auxin signaling Auxin receptors eg TIR1 are E3 ubiquitin ligases! Upon binding auxin they activate complexes targeting AUX/IAA proteins for 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 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

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 ABP1 is a different IAA receptor localized in ER Stimulates PM H+ pump by sending it to PM & keeping it there. Does not affect gene expression! Some "late genes" synthesize ethylene (normally a wounding response): how 2,4-D kills?

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