lec_359713_ppt

7/28/2019 lec_359713_ppt

1/59

Physiology of flowering plant

Molecular level

7/28/2019 lec_359713_ppt

2/59

Molecular studies on flowering crops

Basic knowledge

genes, gene expression profilecontrol of gene expression

Practical aspect

e.g. breeding/improvement

7/28/2019 lec_359713_ppt

3/59

Flowering

At shoot apex

Induction to InitiationtoSpecification

VegetativetoReproductive

Indeterminateto Determinate

Shoot apical meristemto

Inflorescence meristemtoFloral meristem (primordia)

7/28/2019 lec_359713_ppt

4/59

Flowering Signal

Hormone

Temperature

Photoperiod

Autonomous

environment/endogenous

7/28/2019 lec_359713_ppt

5/59

Floral stimulus production

following inducing signal

flowering switch to turn on

florigen

Site of flowering commitment

shoot apex: require sufficient amount of

floral stimulus for continuous flower productionleaf: commit to continuously production of

floral stimulus(irreversible)

7/28/2019 lec_359713_ppt

6/59

Florigen: shoot apex or leaf

Impatiens purple flower

Short day for flowering

5 SD: flowering

SD to LD: continue flowering

SD toremove leavesto LD:leaves with purple petals

7/28/2019 lec_359713_ppt

7/59

Florigen: shoot apex or leaf

Impatiens red flower

Short day for flowering

5 SD: flowering

ReturntoLD: vegetative stage at inner whorls

Require continuous supply of inducing signal

7/28/2019 lec_359713_ppt

8/59

Flowering genes expressed in young leaf

Maize: intermediate

Arabidopsis: constans

7/28/2019 lec_359713_ppt

9/59

Genes in Flower Development

Structural gene

Flower organ

Flower colorFlower scent

Regulatory gene

Protein product involved in controllingexpression of other genes

Via protein-DNA interaction

7/28/2019 lec_359713_ppt

10/59

Flowering genes

Timing

Meristem identity

Organ identity

7/28/2019 lec_359713_ppt

11/59

Approaches

Flowering mutant

Gene identification

Transformation

Mutant complementation

7/28/2019 lec_359713_ppt

12/59

Evolutionary diversificationof organisms

Alteration of developmental events

Variationin structure and regulation of genes

controlling developmental mechanism

Why flowering?

7/28/2019 lec_359713_ppt

13/59

Flowers: invariant pattern and organization

Perianth/Reproductive organs

Varied number, size and position

Why flowering?

7/28/2019 lec_359713_ppt

14/59

Study model: Arabidopsis and Snapdragon

Common characteristics:

Floral-specific expression with different roles

Identified as homeotic genes

Control specification of meristem

and organ identity of flower

Flowering genes

7/28/2019 lec_359713_ppt

15/59

2 classes: meristem identity genes

eg, LFY CAL AP1

organ identity genes

eg,AP2 AP3 PI AG

Most genes encode proteins with

homologous regions of ~ 260 amino acid

sequence similarity: common ancestor

Flowering genes

7/28/2019 lec_359713_ppt

16/59

Highly conserved region about 57 amino acid

called MADS box

also found in yeast and human

Regulatory gene family: transcription factor

MADS box gene in other crops:

tomato tobacco potato petunia

Flowering genes

7/28/2019 lec_359713_ppt

17/59

Homeotic gene: identity of organs/body parts

pattern and position

Sequence-specificDNA-bindingmoiety:

animal: homeodomain (homeobox gene)

plant leaf: homeodomain protein

floral organ: MADS box protein/ gene

7/28/2019 lec_359713_ppt

18/59

Meristem identity genes

Meristem: SAM (indeterminate) for shoot

IM (indeterminate) for inflorescence

FM (determinate)for flower

7/28/2019 lec_359713_ppt

19/59


Inflorescence meristem

Mutant: early flowering in Arabidopsis

Conversion of IMto FM

Terminal flower

tfl

TFL protein

Negative regulatorofLFYandAPgenes

7/28/2019 lec_359713_ppt

20/59


Floral meristem

Mutant: partial conversion ofFM to IMLeafyin Arabidopsis

Floricaula in Snapdragon

LFY and FLO protein

Positive regulatorof AF3 and PI genes

7/28/2019 lec_359713_ppt

21/59


Floral meristem

Mutant: indeterminate flower within flower

(sepal, petal, petal etc)

Agamous (AG) in Arabidopsis

Plena (PLE) in SnapdragonProtein: putative transcription factor

7/28/2019 lec_359713_ppt

22/59

Meristem maintenance genes

Meristem: - small, dense, large nuclei

- to supply new cells

- undifferentiated cells (central)

- daughter cells with

specific developmental fates (subdistal)

7/28/2019 lec_359713_ppt

23/59


Mutant: no meristem (strong allele)

Reduced number of meristematic cells

No effect of root meristem

Shoot meristemless, stm

stm-5mutant: 1-2 leaves then terminate

leaf primordia consume central zone

7/28/2019 lec_359713_ppt

24/59


STM protein:

Produced throughout development

Maintain shoot and floral meristem

Inhibit differentiation in central zone

Activate cell division/proliferation

7/28/2019 lec_359713_ppt

25/59

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

7/28/2019 lec_359713_ppt

26/59

Floral Initiation Process (FLIP)

Transition from early to lateinflorescence

Loss ofindeterminate growth

Inhibit inflorescence program

Inhibit leaf, lateral shoot development

Initiate specific floral organ

Activate perianth development

Inhibit reproductive organ development

7/28/2019 lec_359713_ppt

27/59

FLIP genes

TFL LFY AP1 AP2

TFL: timing of phase transition

Tflmutant: correct sequence of development

early boltingearly flowering

reduced number of inflorescence internode

7/28/2019 lec_359713_ppt

28/59

LFY/AP1/AP2: required in combination

rapid and complete transitionMutant: gradual transition from inflo. to flower

flower-like lateral shoot

leaf in first whorl

reproductive organs in outer whorls

etc.

Late in flower development

ReduceFLIPgenes, increasegametegenes

7/28/2019 lec_359713_ppt

29/59

Floral Organ Identity

Organs with appropriate identity for their positions

ABCmodel3 classes of genes: A, B and C

workingindividual and in pair

A and C inhibit/antagonize each other

(no simultaneous functions)

7/28/2019 lec_359713_ppt

30/59

1 2 3 4

A sepals whorl 1

A+B petals whorl 2

B+C stamens whorl 3C carpel and determinacy whorl 4

A CB

7/28/2019 lec_359713_ppt

31/59

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

7/28/2019 lec_359713_ppt

32/59

A mutant

abnormal in whorl =

abnormal in organ =

B mutant

abnormal in whorl =

abnormal in organ =

C mutant

abnormal in whorl =

abnormal in organ =

7/28/2019 lec_359713_ppt

33/59

AP1, SQUA

Mutant

sepaltoleaves and no petal

Class =

AP2

Mutant

sepalstoleaves or carpels

petalstostamens

Class=

7/28/2019 lec_359713_ppt

34/59

AP3, DEF

Mutant

petalsto sepalsand stamensto carpels

Class=

AG, PLE

Mutant

stamenstopetalsandcarpelstosepals

Class=

7/28/2019 lec_359713_ppt

35/59

A-class mutantwith different phenotypes

Varied from predicted pattern

Some floral homeotic genes (MADS box)

not follow ABC model: newE-class

control 3 inner whorls and determinacy

ABC modelnecessary but not sufficient

**D-class for ovule identity**

7/28/2019 lec_359713_ppt

36/59

E-class or Identity mediating factors

Imgenes: MADS boxgenes

Transcription factor

arabidopsis SEP

petunia FBP2

tomato TM5

Mutants: changes in organ identity

in 3 inner whorls

loss ofdeterminacy

7/28/2019 lec_359713_ppt

37/59

Arabidopsistriplemutant (sep1 sep2 sep3)

4 sepals

4 sepals

6 sepals

new mutant flowerpetunia FBP2: functional equivalent toSEP protein

(complementation ofsepmutant)

E-classessential for function ofB and C class

7/28/2019 lec_359713_ppt

38/59

Revised ABC model

B

Im/E class

A and C

Other factors

sepal petal stamen carpel

7/28/2019 lec_359713_ppt

39/59

Quartet model of floral organ identity

interaction between MADS-domain proteins

to form DNA bindingdimers

B-classprotein form dimer with each other

or withA-classprotein

C-classprotein withE-classprotein

ternaryorquaternarycomplex

B- andC-classprotein with

A-classandE-classprotein

7/28/2019 lec_359713_ppt

40/59

Floral organ identity

controlled by 4 different combinations of

4 floral homeotic proteins

e.g. Arabidopsiswhorl 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 SEPwhorl 4: C-class AG, E-class SEP heterodimer

7/28/2019 lec_359713_ppt

41/59

Blooming gene

When to flower

winter spring summer

too early: no pollinating insecttoo late: not enough time to make seed (winter)

one gene: CONSTANSin Arabidopsis

control flowering time

CONSTANS protein helps measure day length

7/28/2019 lec_359713_ppt

42/59

Quality of light

perceived by 2 light receptors

cryptochrome 2 responds to blue light

phytochrome A responds to red light

CONSTANS protein: amount above threshold

Light receptors: activated

Sunlight: late afternoon

time forflowering

**hundreds of genes involved to build flower**

7/28/2019 lec_359713_ppt

43/59

Color and Color pattern

Flower color: important for pollination

Different perception of color

red flower visible to hummingbird

-- colorless to bee

Changes in petal color : effect on pollinator type

Color pattern: differential accumulation of pigment

7/28/2019 lec_359713_ppt

44/59


Flower color:

Accumulation of flavonoids

Major pigments: anthocyanins

orange, red and purple

Vacuole: site of anthocyanin accumulation

Transport as glutathione conjugate

7/28/2019 lec_359713_ppt

45/59

Anthocyanin

synthesis

pathway

Biosynthesis

enzymes/genes

identified

Flower Color

7/28/2019 lec_359713_ppt

46/59

Anthocyanin synthesis pathway

regulation at transcriptional level

Different colors: different enzyme activities or

substrate/precursoravailability in different steps

Mutations: accumulation of intermediates

new color

Flower Color

7/28/2019 lec_359713_ppt

47/59

Factors on flower perception

co-pigmentation

vacuolar pH

cell shape

Flower Color

7/28/2019 lec_359713_ppt

48/59

Co-pigmentation

anthocyanin and flavonols / flavones

shift in absorption spectrum

differential gene expression:

different enzyme activities

changes in pigment ratio

Flower Color

7/28/2019 lec_359713_ppt

49/59

Vacuolar pH

pH increase blueingseven loci (ph1-ph7) control pH in petunia

mutation of theph loci

effect on pH in petal extract

but not on anthocyanin composition

regulatory genes?

Flower Color

7/28/2019 lec_359713_ppt

50/59

Cell shape

effect on optical properties

conical shape: higher light absorption

appear velvet sheen

flat shape: faint color

Flower Color

7/28/2019 lec_359713_ppt

51/59

Flower Color

Cell-shape controlling gene: mixta

homolog of gene for Myb-domain protein

proposed function: regulatory gene

molecular mechanism: still not known

7/28/2019 lec_359713_ppt

52/59


Color pattern

cell-specific accumulation of pigments

specified by expression pattern of

regulatory genes that control

anthocyanin-synthesis genes

7/28/2019 lec_359713_ppt

53/59

Color pattern

mutant with altered pigment synthesis

mutated structural (enzyme) genes

mutated regulatory genes

Two classes of regulatory genes identified

TF with MYB domain

TF with bHLH motif

7/28/2019 lec_359713_ppt

54/59

Color pattern

Target genes to be regulated

specific cis (responsive) elements

essential for protein-DNA interaction

resulting in transcription activation

species-specific sequence

spatial / temporal specific sequence

7/28/2019 lec_359713_ppt

55/59

Color and color pattern

Many factors still unknown

More information leads to applied research

Genetic engineered cutflowers

with novel color and color pattern

7/28/2019 lec_359713_ppt

56/59

Ornamental crop ImprovementColor

Fragrance

Nectar

Shape

Vase life

Disease resistance

7/28/2019 lec_359713_ppt

57/59

Transformation

(cocultivation with Agrobacterium)

Rose Chrysanthemum

Carnation Tulip

Lily Freesia

Snapdragon Anthurium

Embryogenic callus

Leaf Peduncle Petal Stem

7/28/2019 lec_359713_ppt

58/59

Molecular breeding

Gene transformationthenSelection

Flower color

Maize dfrtopetunia: brick-red petunia

Petunia mum gerbera rose chs

Cosuppression/Antisense technique

Various pattern and color

white pale pink cream etc.

7/28/2019 lec_359713_ppt

59/59

lec_359713_ppt

Documents