1. FLOWER DEVELOPMENT by
Ms. Varsha Gaitonde

2. Genetic Analysis of Flower Development

3. Floral organs- Function
SEPAL Encloses and protects bud
PETAL Attracts pollinator
STAMEN Produces pollen
CARPEL Produces egg

4. FLOWER DEVELOPMENT
At a certain stage of plant development, the apical meristem switches program
from a leaf-producing to a flower-producing tissue
At this stage, the apical meristem becomes an inflorescence meristem (IM)
The IM forms a number of primitive primordia that later develops into sepal,
petal, carpel and stamen

5. Flowers of most Eudicot species are composed of 4 floral organ types:
In 1991, E S. Coen. & E. M. Meyerowitz proposed the ABC Model: To explain how floral whorls develop in Arabidopsis thaliana and Antirrhinum majus
Flowers of most Eudicot species are composed of 4 floral organ types:
Sepals
Petals
Stamens (Androecium- Male) and
Carpels (Gynoecium- Female)
These 4 components are all arranged in individual whorls around the meristem
Most of the genes of ABCDE model are MADS-box genes
Carpels
Stamens
Petals
Sepals
Fig: Arabidopsis showing 4 floral organs

6. MADS-box
The MADS box is a conserved sequence motif found in genes which comprise the MADS-box gene family
The MADS box encodes the DNA-binding MADS domain
The length of the MADS-box are in the range of 168 to 180 base pairs
Origin:
MCM1 from the budding yeast, Saccharomyces cerevisiae,
AGAMOUS from the thale cress Arabidopsis thaliana,
DEFICIENS from the snapdragon Antirrhinum majus
SRF (serum response factor) from the human Homo sapiens
In plants, MADS-box genes are involved in controlling all major aspects of development, including male & female gametophyte development, embryo and seed development, as well as root, flower and fruit development,  floral organ identity and flowering time determination

7. The Signal to Flower
In order for flowers to develop two important genetic changes must occur -
Change from vegetative to floral state
Commitment to from flowers
Signals that indicates it’s time to flower
Maturity of the plant
Temperature
Photoperiodism

9. To understand floral development, researchers have isolated single gene mutants that resulted in homeotic transformations.
Homeotic mutations cause cells to develop into normal organs but in an inappropriate position
Homeotic genes help to determine the identity of tissues during development
Plant homeotic genes = MADS-box
Arabidopsis researchers have identified several mutants with altered flower development. These homeotic (MADS-box) genes were divided into three classes: A, B, and C

10. History of Flower Development Model
Coen, E. S., and Meyerowitz, E. M. The war of the whorls: Genetic interactions controlling flower development, Nature, 1991, 353:
ABC Model
Colombo, L., Franken, J., Koetje, E. et al., The Petunia MADS box gene FBP11 determines ovule identity, Plant Cell, 1995, 7:
ABCD Model
Theissen, G., Development of floral organ identity: Stories from the MADS house, Curr. Opin. Plant Biol., 2001, 4:
ABCDE Model
Theissen, G., Saedler, H., Floral quartets, Nature, 2001, 409:
Quartets Model

11. ABCDE Model of Flower Development
This model developed on the basis of Arabidopsis thaliana and Snapdragon mutants. Most of the genes of ABCDE model are MADS-box genes.
Class A genes (APETALA1, APETALA2) controls sepal development & together with class B genes, regulates the formation of petals. Antirrhinum: LIPLESS 1 and 2
Class B genes (e.g. PISTILLATA, and APETALA3), together with class C genes, mediates stamen development. Antirrhinum: DEFICIENS (DEF) and GLOBOSA (GLO)
Class C genes (e.g., AGAMOUS), determines the formation of carpel. Antirrhinum: PLENA (PLE)
The class D genes (e.g., SEEDSTICK, and SHATTERPROOF) specify the identity of the ovule. Petunia: FBP7 and FBP11
Class E genes (e.g., SEPALLATA), expressed in the entire floral meristem, & are necessary. (SEP1, SEP2, SEP3 and SEP4)

12. ABCDE Model of Flower Development
(Dornelas & Dornelas 2005)

13. Mutations in Floral Organ Identify Genes
Wild Type
AP1 & AP2
AP3 & PI AG
SEP

14. Properties of Arabidopsis thaliana
Six weeks generation time (plant to plant)
Small
Easy to grow and cross
Relatively small genome
- 5 chromosomes
- 125 Mb (corn is 5625 Mb)
Easily mutagenized

15. petals transformed into stamens sepals into carpels. Class A mutant
SINGLE GENE MUTANTS
i) APETALA2 (AP2) mutant
petals transformed into stamens
sepals into carpels.
Class A mutant
AP2 is required for formation of petals and sepals

16. AP3 and PI are required to make petals and stamens
ii) APETALA3 (AP3) and PISTILLATA (PI) mutants
petals transformed into sepals
stamens transformed into carpels
Class B
AP3 and PI are required to make petals and stamens

17. AG is required for formation of stamens and carpels
iii) AGAMOUS (AG) mutant
stamens transformed into sepals
carpels transformed into petals
Class C
AG is required for formation of stamens and carpels

18. The ABC model of floral development
APETALA2 mutant (gene A silenced)
Stamen & carpel only C A
APETALA3 and/or PISTILLATA mutant (gene B silenced)
Sepal & carpel only B A
AGAMOUS mutant (gene C silenced)
Sepal & petal only

19. A Model for Floral Development
Meyerowitz et al B C A

20. Validity of the ABC model of floral development (Double mutants)
Using the model to make predictions of what the double mutant
plants will look like
For example, AP2 : AP3 (lacks both A function and B function) can’t make sepals, petals, or stamens
Only ‘C’ functions will be expressed in every whorl due to the lack
of ‘A’ functions
Therefore all whorls should look like carpels B A C

21. AP2: AP3
all carpels

22. What about AP3:AG (lacking B and C functions)?
Can’t make petals, stamens, or carpels.
‘A’ functions should be expressed in every whorl,
thus sepals are produced in every whorl B A C

23. AP3: AG
sepals in every whorl

24. The ABC model of floral development (Triple mutant )
Triple mutant (genes A, B & C silenced)
Leaf-like structures growing in place of floral parts.

25. A number of candidates for A, B and C class gene have now been identified: representative examples of A class - AP1 and AP2,
B class - AP3 and PI and
C class - AG
Members of the A and C class of genes are mutually anatagonistic, and both A and C class genes upregulate B-class genes. A and C-class genes can also upregulate their own expression.

26. Extension of ABC Model Experiment
ufo and ask1 mutants
Two prominent examples of this are ask1 (arabidopsis skp1-like1) and ufo (unusual floral organs), which are mutants in two components of the SCF (Skp1-Cullin-F-box protein) ubiquitin ligase complex.
As a consequence of cell proliferation, the two domains move farther apart until they separate.

27. Auxin perception and transport in developing flowers
‘pumping’ of auxin is mediated by members of the PIN and AUX families, with the former being auxin efflux carriers and the latter influx ones
Disruption of either auxin transport (corresponding to a PIN mutant) or its perception (corresponding to an ARF mutant) can cause flowers to form abnormal structures.

28. Utility Development of male sterile line
Mutating B gene. Ex: Antirrhinum
Male sterile plants can be of greater use in hybrid seed production
Development of double flower in ornamentals
Mutating C gene. Ex; Petunia, Antirrhinum (ple)
Control of fruit/seed shattering
Mutating D gene (stk & shp)
Development of unique flower form. Mutating E gene (sepallatta) Ex: Green Rose
If SHATTERPROOF1 (SHP1) and SHATTERPROOF2 (SHP2) are mutated, the seed pods fail to shatter, or burst.  They can be inserted into rapeseed or other Cole crops to prevent pods from shattering
The ABCDE model has been successful in explaining how a small number of regulatory genes, acting alone and in combination, specify the identity of the floral organs

29. Homologs in rice Rice homologs of arabidopsis ABC genes: Apetala 1 (A)
OsMADS14
OsMADS15
Apetala 3 (B)
OsMADS16
Agamous (C)
OsMADS3
OsMADS58

30. Arabidopsis thaliana: A model plant species

31. SUMMARY A - SEPAL & PETAL B - PETAL & STAMEN C - STAMEN & CARPEL
GENE
A SEPAL & PETAL
B PETAL & STAMEN
C STAMEN & CARPEL
D OVULE SPECIFICATION
E ALL FLORAL ORGANS
UFO &ASK1 MUTANTS - CELL PROLIFERATION
PIN & AUX FAMILIES EFFLUX & INFLUX CARRIERS OF AUXINS

32. Thank You Stamen Carpel Anther Filament Stigma Style Petal Ovary Ovule
Receptacle
Sepal
all stamens = androecium
all carpels = gynoecium
all petals = corolla
all sepals = calyx
Thank You