The flower development in plants

1. FLOWER
DEVELOPMENT
SRINIVAS .S .SURESH
M.Sc LIFE SCIENCES
ROLL NO. 2019MLS10
Department of life sciences
Central university of Karnataka.

3. The plant start post-embryonic development
after seed germination at a certain time period
in the life cycle they only continue the
vegetative growth .
This vegetative plants enters in the process of
floral transition and it start the reproductive
phase.
Sexual reproduction is restricted in an organ or
in a part of the plant which is called flowers,
which are developed on a structure which is
called inflorescence.
FLORAL TRANSITION
Image source : Liu et al.(2009), development ,136,33799-91.

4. Regulation of flower development
Arabidopsis flowers originate as small groups of undifferentiated cells
called flower meristems (FM) on the flanks of the inflorescence
meristem(IM).
IM is indeterminate structures
flowers are determinate structures
Vegetative meristem Inflorescence meristem Flower meristem

5. Flower development can be divided into four steps.
Vegetative growth reproductive growth Flowering time genes
Response to environmental and endogenous
1.
2. Signals from flowering time pathways Activation of first inflorescence meristem identity genes
(TERMINAL FLOWER)
Small group of floral meristem identity genes (LEAFY,
APETALA, and CAULIFLOWER specify floral identity.
3.Floral meristem identity genes activate the floral organ identity genes APETALA (both floral meristem and organ
identity), PETALA2, APETALA ,PISTILLATA and AGAMOUS).
4. Floral organ identity genes activate downstream "organ building“ genes.

6. PARASITE TURNS PLANT INTO “FLOWERLESS ZOOMBIES”
“Witches broom”
Parasite – ‘Phytoplasma’
Convert Flowers into
vegetative tissues

7. FLORAL DEVELOPMENT
Floral meristem
Identity Genes
CONVERT SHOOT
INTO FLOWER
1)LEAFY(LFY)
2)APEATALA1(AP1)
3)CAULIFLOWER(CAL)
Floral organ
Identity Genes
Control floral
Identity
1)APEATAL1(AP1)
2)AP2
3)AP3
4)PISTILLATA(PI)
5)AGAMOUS(AG)

8. Genetic and environmental factors which regulates the
timing of the transition.
During the vegetative process reproductive phases are
repressed.
TFL is basically TERMINAL FLOWER1 and a mutant was
identified in this gene where the plant flowered early and
branches are getting terminated with a single terminal
flower.
In Arabidopsis after transition the shoot apex get converted
into inflorescence meristem and this inflorescence meristem
has a mixture of property.
TFL1 - Negative regulator of flowering .
tfl mutant this shoot like structure get terminated with a
single determinate flower.
WT tlf-1
efl
Floral Transition :Terminal Flower (TFL)
Image source: Shannon & Meeks-Wagner (1991), Plant cell, 3.877-92

9. LEAFY is activator of flowering.
Arabidopsis thaliana plant there are three types of
structure.
This is an architecture of Arabidopsis inflorescence. In
wild type you have this co-florescence and then you
have this final flowers,
leafy mutant the later flowers which are getting
converted like shoot like structure means loss of floral
identity.
TFL LEAFY
shoot identity or
shoot like structure
inflorescence
identity
floral meristem
Arabidopsis 3
metameric types
1. Type ,Rosette
2. Type , coflorescence
bearing bracts
LFY
3 Type Flower bearing
without bracts
Floral Transition : LEAFY (LFY)
Image Source: Schultz & Haughn (1991) Plant Cell, 3,771 -81

10. CAULIFLOWER(CA), promote a floral-meristem fate
But CAULIFLOWER, does not show its effects unless it is with AP1 mutant.
CAL AP1 double mutants have inflorescence meristems developing in place of floral
meristems.
The CAULIFLOWER gene of cultivated cauliflower has a stop codon that inactivates
the gene product.
This prevents the transition for inflorescence to floral meristems.
In Snapdragon Floricaula (flo) mutants fail to undergo transition from inflorescence
meristem to floral meristem ,flower have appearance of inflorescence shoot
Snapdragon

11. TFL is regulating even
the first step of
transition . then LEAFY
is ensuring a proper
floral meristem identity,
in the peripheral region
and these are the typical
schematic diagram of
other mutants .
Wild leafy apetala1 leafy terminal 35S:LFY
apeatala1 flower
Arabidopsis 3
metameric types
1. Type ,Rosette
2. Type, coflorescence
bearing bracts
LFY
3 Type Flower bearing
without bracts
TFL1
Floral Transition :Genetic Interaction
Image Source: Weigel , D(1995), Annu.Rev. Genetics,29. 19-39

12. .
LEAFY and AP1 works parallel pathways.
At the center you have high amount of TFL1 expression and you have very
less amount of LEAFY expression. And when you have high amount of TFL,
TFL goes and it repress both AP1 as well as LEAFY in the center region .
In the peripheral region LEAFY is getting activated and, LEAFY also activates
the expression of AP1 and then both LEAFY and AP1 together specify or
provide floral meristem identity to the peripheral meristem.SAM IM/FM
Floral transition
TFL1
LFY
AP1/CAL
Interaction of TFL-LFY-AP1
Image Source: Bla’ zquez et al. (2006) Plant .Mol. Bio 60,855-70

13. Image Source: Ratcliffe et. al (1999) , Development 126, 1109-20

14. If we summarize this interaction, so
during vegetative phase TFL1 level
very high. And then during floral
meristem stage LFY, AP1, AP2.

15. The activity of LEAFY1 and AP1 is regulated by
two another important genes FT and SOC1. And
these genes are called flowering time genes and
both are positive regulator of AP1 and LEAFY1
GENETIC PATHWAYS REGULATING FLOWERING TIME

16. Figure 1. Five Major Pathways for Flowering Time Control in
Arabidopsis: Autonomous, Vernalization, Photoperiod, Aging, and
Gibberellin (GA) Pathways.

17. Image Source : Plant cell , Baurle & Dean (2006) Cell , 125 ,655,64

18. Inflorescence meristem it will become floral
primordia. Which activate floral primordia specific
genes and important in regulating the floral organ
patterning. flower specific organs and flower
specific organs are sepal, petals, stamen and carpals.
by a class of genes called A B C and E genes called
floral organ identity genes. LEAFY activate AP1, A
class gene. LEAFY together with UFO activate B
class gene which is AP3 and PI in Arabidopsis and
LEAFY together with WUSCHEL activate
AGAMOUS, AG gene which is basically C class
genes . there are four E class gene SEPALLATA1, 2,
3 and 4.
Image Source: Krizek & Fletchger (2005), Nat Rev Genet , 6, 688 -98

19. Image Source ; Krizek & Fletcher (2005), Nat Rev Genet
ABCE MODEL FOR FLORAL ORGAN PATTERNING

22. How do the floral organ identity genes act?
The floral-organ identity genes encode transcription factors.
AP2 is a members of the plant-specific AP2/ERF family of transcription factors.
Most floral homeotic genes, encode MADS domain transcription factors, which contain a DNA binding
domain that is conserved among eukaryotes.
These proteins form dimers to bind to the ‘CA rG (CC(A/T)6GG) box’ DNA target sequence.
The finding that floral MADS domain proteins can associate in higher-order complexes has led to the
formulation of a biochemical QUARTETMODEL3

24. REFERENCES :
1)https://plantcellbiology.masters.grkraj.org/html/Plant_Growth_And_Develo
pment10-Physiology_Of_Flowering.htm?hcb=1
2)www.iflscience.com
3)http://www.ncbi.nlm.nih.gov/
4)http://www.biomedcentral.com/
5)http://embor.embopress.org/

25. THANK YOU