physiology of flowering plant molecular level
DESCRIPTION
Physiology of flowering plant Molecular level. Molecular studies on flowering crops Basic knowledge genes, gene expression profile control of gene expression Practical aspect e.g. breeding/improvement. Flowering At shoot apex Induction to Initiation to Specification - PowerPoint PPT PresentationTRANSCRIPT
Physiology of flowering plantMolecular level
Molecular studies on flowering cropsBasic knowledge
genes, gene expression profilecontrol of gene expression
Practical aspect e.g. breeding/improvement
FloweringAt shoot apex
Induction to Initiation to SpecificationVegetative to Reproductive
Indeterminate to DeterminateShoot apical meristem toInflorescence meristem toFloral meristem (primordia)
Flowering SignalHormoneTemperaturePhotoperiod Autonomous
environment/endogenous
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)
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
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
Flowering genes expressed in young leaf
Maize: intermediateArabidopsis: constans
Genes in Flower DevelopmentStructural gene
Flower organFlower colorFlower scent
Regulatory geneProtein product involved in controlling
expression of other genesVia protein-DNA interaction
Flowering genesTimingMeristem identityOrgan identity
ApproachesFlowering mutantGene identificationTransformationMutant complementation
Evolutionary diversification of organismsAlteration of developmental events
Variation in structure and regulation of genes controlling developmental mechanism
Why flowering?
Flowers: invariant pattern and organizationPerianth/Reproductive organs
Varied number, size and position
Why flowering?
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
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
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
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
Meristem identity genes
Meristem: SAM (indeterminate) for shootIM (indeterminate) for inflorescence
FM (determinate) for flower
Meristem identity genes
Inflorescence meristemMutant: early flowering in ArabidopsisConversion of IM to FMTerminal flowertflTFL proteinNegative regulator of LFY and AP genes
Meristem identity genesFloral meristem
Mutant: partial conversion of FM to IMLeafy in ArabidopsisFloricaula in SnapdragonLFY and FLO proteinPositive regulator of AF3 and PI genes
Meristem identity genesFloral meristem
Mutant: indeterminate flower within flower(sepal, petal, petal etc)
Agamous (AG) in ArabidopsisPlena (PLE) in SnapdragonProtein: putative transcription factor
Meristem maintenance genes
Meristem: - small, dense, large nuclei- to supply new cells- undifferentiated cells (central)- daughter cells with specific developmental fates (subdistal)
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
Meristem maintenance genesSTM protein:
Produced throughout developmentMaintain shoot and floral meristem Inhibit differentiation in central zoneActivate cell division/proliferation
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
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
FLIP genesTFL LFY AP1 AP2
TFL: timing of phase transitionTfl mutant: correct sequence of development
early boltingearly floweringreduced number of inflorescence internode
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
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)
1 2 3 4
A sepals whorl 1A+B petals whorl 2B+C stamens whorl 3C carpel and determinacy whorl 4
A C
B
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
A mutantabnormal in whorl =abnormal in organ =
B mutant abnormal in whorl = abnormal in organ =
C mutant abnormal in whorl = abnormal in organ =
AP1, SQUAMutant
sepal to leaves and no petalClass =
AP2Mutant
sepals to leaves or carpelspetals to stamens
Class=
AP3, DEFMutant
petals to sepals and stamens to carpelsClass=
AG, PLEMutant
stamens to petals and carpels to sepalsClass=
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
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
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
Revised ABC modelBIm/E classA and COther factors sepal petal stamen carpel
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
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
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
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
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
Color and Color patternFlower color:
Accumulation of flavonoidsMajor pigments: anthocyanins
orange, red and purpleVacuole: site of anthocyanin accumulationTransport as glutathione conjugate
Anthocyanin synthesis pathway
Biosynthesisenzymes/genes identified
Flower Color
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
Factors on flower perceptionco-pigmentationvacuolar pHcell shape
Flower Color
Co-pigmentationanthocyanin and flavonols / flavonesshift in absorption spectrum
differential gene expression:different enzyme activitieschanges in pigment ratio
Flower Color
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
Cell shapeeffect on optical propertiesconical shape: higher light absorption
appear velvet sheenflat shape: faint color
Flower Color
Flower Color
Cell-shape controlling gene: mixtahomolog of gene for Myb-domain proteinproposed function: regulatory genemolecular mechanism: still not known
Color and Color pattern
Color patterncell-specific accumulation of pigmentsspecified by expression pattern of
regulatory genes that control anthocyanin-synthesis genes
Color patternmutant with altered pigment synthesis
mutated structural (enzyme) genesmutated regulatory genes
Two classes of regulatory genes identifiedTF with MYB domainTF with bHLH motif
Color patternTarget genes to be regulated
specific cis (responsive) elements essential for protein-DNA interactionresulting in transcription activation
species-specific sequencespatial / temporal specific sequence
Color and color patternMany factors still unknownMore information leads to applied researchGenetic engineered cutflowers
with novel color and color pattern
Ornamental crop ImprovementColor
FragranceNectarShape
Vase lifeDisease resistance
Transformation (cocultivation with Agrobacterium)Rose ChrysanthemumCarnation TulipLily FreesiaSnapdragon Anthurium
Embryogenic callusLeaf Peduncle PetalStem
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.
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)