Flowering in plants(Arabidopsis) ABC Model My youtube videos: https://youtu.be/9SxSpNEQj_g https://youtu.be/-D6OGm8YbXc Set of four genes class A, B & C are involved in giving identity of different whorls. 4 pathways are involved - Photoperiodism, autonomous pathway, vernalization & giberlleic acid

1. Flowering in
plants
ABC Model

2. Flowering genes
Floral meristem
identity genes
Floral organ
identity genes
LEAFY (LFY)
APETALA1 (AP1)
CAULIFLOWER(CAL)
APETALA1 (AP1)
APETALA2 (AP2)
APETALA3 (AP3)
PISTILLATA (PI)
AGAMOUS(AG)
Early stages
Transcription factors

3. FLORAL PATHWAY
INTEGRATORS
Gibberellic
acid
LEAFY
Photoperiodic
pathway
Constans CO
FT gene
FT protein
translocation
FD
protein
LEAFY
Autonomous
pathway
FLC Vernalization
Vegetative
meristem
Flowering
meristem

4. ABC Model

5. Class of genes Gene names Development
A APETALA1 (AP1)
APETALA2 (AP2)
Whorls 1 & 2
B APETALA3 (AP3)
PISTILLATA (PI)
Whorls 2 & 3
C AGAMOUS(AG) Whorls 3 & 4
Sepals
Petals
Stamens
Carpels
HOX genes with MADS domain instead of homeodomain found in humans!

6. 01

7. 02

8. 03

9. 04

10. 04 ABCDE Model

11. Floral organ development is controlled by overlapping expression of
‘A’ class, ‘B’ class and ‘C’ class genes in different whorls. In an
Arabidopsis mutant, the flowers had sepals, sepals, carpels & carpels
in four whorls. Mutation in which one of the following is the cause
of a mutant phenotype?
a. Class ‘A’ gene alone
b. Class ‘B’ gene alone
c. Both Class ‘A’ & ‘B’ genes
d. Class ‘C’ gene alone
DEC 2015

12. Individual and overlapping expression of homeotic genes in adjacent
whorls of a flower determine the pattern of floral organ
development. In an Arabidopsis mutant, floral organs are distributed
as follows:
Whorl 1- carpel, Whorl 2- stamens, Whorl 3- stamens, Whorl
4-carpel
Loss of function mutation in which one of the following genes would
have caused the above pattern of floral organ development
a. APETALA 2 b. APETALA 3 c. PISTILLATA d. AGAMOUS
DEC 2016

13. JUNE 2016

14. Which one of the following statements about
LEAFY(LFY), a regulatory gene in A. thaliana is correct?
a. LEAFY is involved in floral meristem identity
b. LEAFY is involved in leaf expansion
c. LEAFY is involved in root meristem identity
d. LEAFY is responsible for far-red light mediated
seedling growth
2015 JUNE

15. Which of the floral whorls is affected in
apetala3/pistillata(ap3/pi) mutants?
a. Sepals and petals
b. Petals and stamens
c. Stamens and carpels
d. Sepals and stamens
2013 JUNE

16. Organ identity genes are responsible for correct
positioning of floral organs on floral meristem.
Mutation in them will lead to?
a. Loss of organs from certain whorls
b. More number of organs in certain whorls
c. Appearance of organs at incorrect positions
d. No flower
2009 JUNE

17. Photoperiodic stimulus from leaves to shoot apical
meristem/ floral meristem is transported through:
a. Xylem
b. Phloem
c. Plasmodesmata
d. Apoplast
2008 JUNE

18. Among the following which gene product migrates
from leaves to shoot meristem during transition of
shoot meristem into floral meristem?
a. Flowering locus T
b. Flowering locus D
c. leafy
d. apetala 1
2010 DECEMBER

19. Three classes of genes A, B & C regulate the development of flower
in Arabidopsis. If a loss of function mutation occurs in the type B
genes, what will be the composition of flower whorls?
a. Sepals-Petals-Stamens-Carpels
b. Sepals-Sepals-Stamens-Stamens
c. Sepals-Sepals-Carpels-Carpels
d. Petals-Petals-Stamens-Stamens
DEC 2009

20. The control of flowering is a complex process involving several key regulatory genes. Some
statements on flower development are given below:
A. Two major types of genes regulate floral development: meristem identity & floral organ
identity genes
B. The important genes in Arabidopsis that play key regulatory roles in meristem identity
are: APETALA1, LEAFY and SUPPRESSOR OF CONSTANS 1
C. The genes that determine floral organ identity were discovered as floral homeotic
mutants
D. Most plant homeotic genes belong to a class of related sequence known as FAD box
genes
Which of the following combinations is correct?
a. A, B and C
b. B, C and D
c. A, C and D
d. A, B and D
DEC 2013