Prepare a 10’talk for Friday Feb 27 on plant defense responses or describe interactions between plants & pathogens or symbiontsPrepare a 10’talk for Friday Feb 27 on plant defense responses or describe interactions between plants & pathogens or symbionts

Plant defense responsesPlant defense responses•Hypersensitive responseHypersensitive response•Systemic acquired Systemic acquired resistanceresistance•Innate immunityInnate immunity•Phytoalexin synthesisPhytoalexin synthesis•Defensins and other Defensins and other proteinsproteins•Oxidative burstOxidative burst

Some possible pathogensSome possible pathogens•Agrobacterium tumefaciens Agrobacterium tumefaciens •Agrobacterium rhizogenesAgrobacterium rhizogenes•Pseudomonas syringeaePseudomonas syringeae•Pseudomonas aeruginosaPseudomonas aeruginosa•ViroidsViroids•DNA virusesDNA viruses•RNA virusesRNA viruses•FungiFungi•OomycetesOomycetes

Some possible symbiontsSome possible symbionts•N-fixing bacteriaN-fixing bacteria•N-fixing cyanobacteriaN-fixing cyanobacteria•EndomycorrhizaeEndomycorrhizae•EctomycorrhizaeEctomycorrhizae

Growth regulators1.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

Auxin signalingAuxin receptors eg TIR1 are E3 ubiquitin ligases!Upon binding auxin they activate complexes targeting AUX/IAA proteins for degradation!AUX/IAA inhibit ARFtranscription factors,so this turns on "early genes"Some early genes turn on'late genes" needed for development

Auxin signalingABP1 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

CytokininsDiscovered as factors which induce cultured cells to divideHaberlandt (1913): phloem chemical stimulates division

CytokininsDiscovered as factors which induce cultured cells to divideHaberlandt (1913): phloem chemical stimulates divisionvan Overbeek (1941): coconut milk stimulates division

CytokininsDiscovered as factors which induce cultured cells to divideHaberlandt (1913): phloem chemical stimulates divisionvan Overbeek (1941): coconut milk stimulates divisionMiller… Skoog (1955): degraded DNA stimulates division!

CytokininsDiscovered as factors which induce cultured cells to divideHaberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates divisionMiller… Skoog (1955): degraded DNA stimulates division!Kinetin was the breakdown product

CytokininsDiscovered as factors which induce cultured cells to divideHaberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates divisionMiller… Skoog (1955): degraded DNA stimulates division!Kinetin was the breakdown productDerived from adenine

CytokininsDiscovered as factors which induce cultured cells to divideHaberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates divisionMiller… Skoog (1955): degraded DNA stimulates division!Kinetin was the breakdown productDerived from adenineRequires auxin to stimulate division

CytokininsRequires auxin to stimulate divisionKinetin/auxin determines tissue formed (original fig)

CytokininsRequires auxin to stimulate divisionKinetin/auxin determines tissue formedInspired search for natural cytokininsMiller& Letham (1961) ± simultaneously found zeatin in corn

Kinetin trans- Zeatin

CytokininsMiller& Letham (1961) ± simultaneously found zeatinLater found in many spp including coconut milk

Kinetin trans-Zeatin

CytokininsMiller& Letham (1961) ± simultaneously found zeatinLater found in many spp including coconut milkTrans form is more active,but both exist (& work)Many other natural & synthetics have been identified

CytokininsMany other natural & synthetics have been identifiedLike auxins, many are bound to sugars or nucleotides

CytokininsMany other natural & synthetics have been identifiedLike auxins, many are bound to sugars or nucleotidesInactive, but easily converted

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

Cytokinin SynthesisMost cytokinins are made at root apical meristem & transported to sinks in xylemTherefore have inverse gradientwith IAA

Cytokinin SynthesisMost cytokinins are made at root apical meristem & transported to sinks in xylemTherefore have inverse gradientwith IAAWhy IAA/CK affects development

Cytokinin SynthesisMost cytokinins are made at root apical meristem & transported to sinks in xylemTherefore have inverse gradientwith IAAWhy IAA/CK affects developmentRapidly metabolized by sink

Cytokinin EffectsRegulate cell division• Need mutants defective in CK metabolism or signaling to detect

this in vivo

Cytokinin EffectsRegulate 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 EffectsCytokinins mainly act @ root & shoot meristemsControl 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 ReceptorsReceptors were identified by mutationResemble bacterial 2-component signaling systems

Cytokinin Action1.Cytokinin binds receptor's extracellular domain

Cytokinin Action1.Cytokinin binds receptor's extracellular domain2. Activated protein kinases His kinase & receiver domains

Cytokinin Action1.Cytokinin binds receptor's extracellular domain2. Activated protein kinases His kinase & receiver domains3. Receiver kinases His-P transfer relay protein (AHP)

Cytokinin Action1.Cytokinin binds receptor's extracellular domain2. Activated protein kinases His kinase & receiver domains3. Receiver kinases His-P transfer relay protein (AHP)4. AHP-P enters nucleus & kinases ARR response regulators

Cytokinin Action4. AHP-P enters nucleus & kinases ARR response regulators5. Type B ARR induce type A

Cytokinin Action4. AHP-P enters nucleus & kinases ARR response regulators5. Type B ARR induce type A6. Type A create cytokininresponses

Cytokinin Action4. AHP-P enters nucleus & kinases ARR response regulators5. Type B ARR induce type A6. Type A create cytokininresponses 7. Most other effectors are unknownbut 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

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

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

GibberellinsDiscovered 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

GibberellinsDiscovered by studying "foolish seedling" disease in rice• Kurosawa (1926): fungal filtrate causes these effects• Yabuta (1935): purified gibberellins from filtrates of Gibberella fujikuroi cultures

GibberellinsDiscovered 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

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

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

GibberellinsDiscovered 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 signalingUsed mutants to learn about GA signaling

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

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

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

•Others hit GA signaling•Gid = GA insensitive

Gibberellin signalingUsed 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 signalingUsed 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 signalingUsed 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

GibberellinsGAs 1, 3 & 4 are most bioactiveAct by triggering degradationof DELLA repressors

GibberellinsGAs 1, 3 & 4 are most bioactiveMade at many locations in plantAct by triggering degradationof DELLA repressorsw/o GA DELLA binds & blocks activator (GRAS)

GibberellinsAct by triggering degradation of DELLA repressorsw/o GA DELLA binds & blocks activatorbioactive GA binds GID1; GA-GID1 binds DELLA & marks for

destruction

GibberellinsAct by triggering degradation of DELLA repressorsw/o GA DELLA binds & blocks activatorbioactive GA binds GID1; GA-GID1 binds DELLA & marks for

destructionGA early genes are transcribed, start GA responses