Physiology of flowering plant Molecular level
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Transcript of Physiology of flowering plant Molecular level
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Physiology of flowering plantMolecular level
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Molecular studies on flowering cropsBasic knowledge
genes, gene expression profilecontrol of gene expression
Practical aspect e.g. breeding/improvement
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FloweringAt shoot apex
Induction to Initiation to SpecificationVegetative to Reproductive
Indeterminate to DeterminateShoot apical meristem toInflorescence meristem toFloral meristem (primordia)
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Flowering SignalHormoneTemperaturePhotoperiod Autonomous
environment/endogenous
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Floral stimulus productionfollowing inducing signalflowering switch to turn onflorigen
Site of flowering commitmentshoot apex: require sufficient amount of
floral stimulus for continuous flower productionleaf: commit to continuously production of
floral stimulus (irreversible)
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Florigen: shoot apex or leaf
Impatiens purple flowerShort day for flowering
5 SD: floweringSD to LD: continue flowering
SD to remove leaves to LD:leaves with purple petals
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Florigen: shoot apex or leaf
Impatiens red flowerShort day for flowering
5 SD: floweringReturn to LD: vegetative stage at inner whorls
Require continuous supply of inducing signal
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Flowering genes expressed in young leaf
Maize: intermediateArabidopsis: constans
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Genes in Flower DevelopmentStructural gene
Flower organFlower colorFlower scent
Regulatory geneProtein product involved in controlling
expression of other genesVia protein-DNA interaction
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Flowering genesTimingMeristem identityOrgan identity
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ApproachesFlowering mutantGene identificationTransformationMutant complementation
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Evolutionary diversification of organismsAlteration of developmental events
Variation in structure and regulation of genes controlling developmental mechanism
Why flowering?
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Flowers: invariant pattern and organizationPerianth/Reproductive organs
Varied number, size and position
Why flowering?
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Study model: Arabidopsis and SnapdragonCommon characteristics:
Floral-specific expression with different roles Identified as homeotic genesControl specification of meristem
and organ identity of flower
Flowering genes
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2 classes: meristem identity geneseg, LFY CAL AP1
organ identity geneseg, AP2 AP3 PI AG
Most genes encode proteins with homologous regions of ~ 260 amino acid
sequence similarity : common ancestor
Flowering genes
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Highly conserved region about 57 amino acidcalled MADS boxalso found in yeast and human
Regulatory gene family: transcription factorMADS box gene in other crops:
tomato tobacco potato petunia
Flowering genes
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Homeotic gene: identity of organs/body partspattern and position
Sequence-specific DNA-binding moiety:animal: homeodomain (homeobox gene)plant leaf: homeodomain proteinfloral organ: MADS box protein / gene
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Meristem identity genes
Meristem: SAM (indeterminate) for shootIM (indeterminate) for inflorescence
FM (determinate) for flower
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Meristem identity genes
Inflorescence meristemMutant: early flowering in ArabidopsisConversion of IM to FMTerminal flowertflTFL proteinNegative regulator of LFY and AP genes
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Meristem identity genesFloral meristem
Mutant: partial conversion of FM to IMLeafy in ArabidopsisFloricaula in SnapdragonLFY and FLO proteinPositive regulator of AF3 and PI genes
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Meristem identity genesFloral meristem
Mutant: indeterminate flower within flower(sepal, petal, petal etc)
Agamous (AG) in ArabidopsisPlena (PLE) in SnapdragonProtein: putative transcription factor
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Meristem maintenance genes
Meristem: - small, dense, large nuclei- to supply new cells- undifferentiated cells (central)- daughter cells with specific developmental fates (subdistal)
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Meristem maintenance genesMutant: no meristem (strong allele)
Reduced number of meristematic cellsNo effect of root meristem
Shoot meristemless, stmstm-5 mutant: 1-2 leaves then terminate
leaf primordia consume central zone
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Meristem maintenance genesSTM protein:
Produced throughout developmentMaintain shoot and floral meristem Inhibit differentiation in central zoneActivate cell division/proliferation
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Floral Initiation Process (FLIP)Arabidopsis structural development
- rosette leaves with compact internode- elongated internode with cauline leaves
and lateral inflorescence (bolting) - nodes without leaves and flowers
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Floral Initiation Process (FLIP)
Transition from early to late inflorescenceLoss of indeterminate growthInhibit inflorescence program
Inhibit leaf, lateral shoot developmentInitiate specific floral organ
Activate perianth developmentInhibit reproductive organ development
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FLIP genesTFL LFY AP1 AP2
TFL: timing of phase transitionTfl mutant: correct sequence of development
early boltingearly floweringreduced number of inflorescence internode
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LFY/AP1/AP2: required in combinationrapid and complete transition
Mutant: gradual transition from inflo. to flowerflower-like lateral shootleaf in first whorlreproductive organs in outer whorlsetc.
Late in flower developmentReduce FLIP genes, increase gamete genes
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Floral Organ IdentityOrgans with appropriate identity for their positions
ABC model3 classes of genes: A, B and Cworking individual and in pairA and C inhibit/antagonize each other
(no simultaneous functions)
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1 2 3 4
A sepals whorl 1A+B petals whorl 2B+C stamens whorl 3C carpel and determinacy whorl 4
A C
B
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ABC model: Developed from floral homeotic mutants
of Arabidopsis and Antirrhinum(flowers with abnormal organ pattern)
Genes identified: MADS-box family(transcription factor with conserved domain) Also work well in petunia, tomato and maize
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A mutantabnormal in whorl =abnormal in organ =
B mutant abnormal in whorl = abnormal in organ =
C mutant abnormal in whorl = abnormal in organ =
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AP1, SQUAMutant
sepal to leaves and no petalClass =
AP2Mutant
sepals to leaves or carpelspetals to stamens
Class=
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AP3, DEFMutant
petals to sepals and stamens to carpelsClass=
AG, PLEMutant
stamens to petals and carpels to sepalsClass=
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A-class mutant with different phenotypesVaried from predicted pattern
Some floral homeotic genes (MADS box)not follow ABC model: new E-classcontrol 3 inner whorls and determinacy
ABC model necessary but not sufficient- ** **D class for ovule identity
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E-class or Identity mediating factors
Im genes: MADS box genesTranscription factor
arabidopsis SEPpetunia FBP2tomato TM5Mutants: changes in organ identity
in 3 inner whorlsloss of determinacy
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Arabidopsis triple mutant (sep1 sep2 sep3)4 sepals 4 sepals6 sepals new mutant flower
petunia FBP2: functional equivalent to SEP protein(complementation of sep mutant)
E-class essential for function of B and C class
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Revised ABC modelBIm/E classA and COther factors sepal petal stamen carpel
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Quartet model of floral organ identityinteraction between MADS-domain proteins
to form DNA binding dimersB-class protein form dimer with each other
or with A-class proteinC-class protein with E-class protein
ternary or quaternary complexB- and C-class protein with A-class and E-class protein
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Floral organ identity controlled by4 different combinations of
4 floral homeotic proteins
e.g. Arabidopsis whorl 1: A- class AP1 homodimer whorl 2: A- class AP1, B- class AP3 and PI, E- class SEP whorl 3: B- class AP3 and PI, C- class AG, E- class SEP whorl 4: C- class AG, E- class SEP heterodimer
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Blooming gene When to flower
winter spring summer too early: no pollinating insect too late: not enough time to make seed (winter)
one gene: CONSTANS in Arabidopsis control flowering time
CONSTANS protein helps measure day length
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Quality of light perceived by 2 light receptors
cryptochrome 2 responds to blue lightph ytochrome A responds to red light
CONSTANS protein: amount above threshold Light receptors: activated
Sunlight: late afternoontime for flowering
** **hundreds of genes involved to build f lower
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Color and Color patternFlower color: important for pollinationDifferent perception of color
red flower – visible to hummingbird-- colorless to bee
Changes in petal color : effect on pollinator typeColor pattern: differential accumulation of pigment
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Color and Color patternFlower color:
Accumulation of flavonoidsMajor pigments: anthocyanins
orange, red and purpleVacuole: site of anthocyanin accumulationTransport as glutathione conjugate
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Anthocyanin synthesis pathway
Biosynthesisenzymes/genes identified
Flower Color
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Anthocyanin synthesis pathwayregulation at transcriptional level
Different colors: different enzyme activities or substrate/precursor availability in different steps
Mutations: accumulation of intermediatesnew color
Flower Color
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Factors on flower perceptionco-pigmentationvacuolar pHcell shape
Flower Color
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Co-pigmentationanthocyanin and flavonols / flavonesshift in absorption spectrum
differential gene expression:different enzyme activitieschanges in pigment ratio
Flower Color
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Vacuolar pHpH increase blueingseven loci (ph1-ph7) control pH in petuniamutation of the ph loci
effect on pH in petal extractbut not on anthocyanin compositionregulatory genes?
Flower Color
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Cell shapeeffect on optical propertiesconical shape: higher light absorption
appear velvet sheenflat shape: faint color
Flower Color
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Flower Color
Cell-shape controlling gene: mixtahomolog of gene for Myb-domain proteinproposed function: regulatory genemolecular mechanism: still not known
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Color and Color pattern
Color patterncell-specific accumulation of pigmentsspecified by expression pattern of
regulatory genes that control anthocyanin-synthesis genes
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Color patternmutant with altered pigment synthesis
mutated structural (enzyme) genesmutated regulatory genes
Two classes of regulatory genes identifiedTF with MYB domainTF with bHLH motif
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Color patternTarget genes to be regulated
specific cis (responsive) elements essential for protein-DNA interactionresulting in transcription activation
species-specific sequencespatial / temporal specific sequence
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Color and color patternMany factors still unknownMore information leads to applied researchGenetic engineered cutflowers
with novel color and color pattern
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Ornamental crop ImprovementColor
FragranceNectarShape
Vase lifeDisease resistance
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Transformation (cocultivation with Agrobacterium)Rose ChrysanthemumCarnation TulipLily FreesiaSnapdragon Anthurium
Embryogenic callusLeaf Peduncle PetalStem
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Molecular breedingGene transformation then Selection
Flower colorMaize dfr to petunia: brick-red petuniaPetunia mum gerbera rose chs
Cosuppression/Antisense techniqueVarious pattern and color
white pale pink cream etc.
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Regulatory gene for anthocyanin pathwayMaize Lc to petunia: red plantSnapdragon del to gerbera:
red leaf and flower scape not in flower
Vase life: ethylene
Scent: s-linalool synthase (monoterpene)