Study of flower development by using ABC, ABCD & ABCDE Model

Flower development is the process by which angiosperms produce a pattern of gene expression in meristems that leads to the appearance of a flower.
A flower is the reproductive structure found in flowering plants.
When plants recognize an opportunity to flower, signals are transmitted through florigen, which involves a variety of genes, including CONSTANS, FLOWERING LOCUS C and FLOWERING LOCUS T.
Florigen is produced in the leaves in reproductively favorable conditions and acts in buds and growing tips to induce a number of different physiological and morphological changes.

1. Floral Development Floral organ identity genes and ABC model.

2. Noor E Sahar MPHIL-Botany 2 nd semester Ma’am Shamim Advanced Physiology 05-06-2025 02

3. Table of Contents Flower Development Genetic Control of Flower Development Floral Organ Identity Genes 01 02 03 03

4. Table of Contents ABCD Model Of Flower Development ABCDE Model Of Flower Development Refrences 04 05 06 04

5. Flower Development 01 05

6. Flower development is the process by which angiosperms produce a pattern of gene expression in meristems that leads to the appearance of a flower. A flower is the reproductive structure found in flowering plants. There are three physiological developments that must occur in order for reproduction to take place: Flower Development 06

7. Physiological Developments Necessary For Reproduction the plant must pass from sexual immaturity into a sexually mature state. the apical meristem must transform from a vegetative meristem into a floral meristem or inflorescence the flowers individual organs must grow (modeled using the ABC model ) 07

8. Genetic Control of Flower Development 02 08

9. Genetic Control of Flower Development When plants recognize an opportunity to flower, signals are transmitted through florigen , which involves a variety of genes, including CONSTANS, FLOWERING LOCUS C and FLOWERING LOCUS T. Florigen is produced in the leaves in reproductively favorable conditions and acts in buds and growing tips to induce a number of different physiological and morphological changes. 09

10. Three Types of Genes Regulate Floral Development Floral Organ Identity Genes The proteins encoded are transcription factors that likely control the expression of other genes whose products are involved in the formation or function of floral organs. Cadastral Genes Regulators of the floral organ identity genes by setting boundaries for their expression. (The word cadastre refers to a map) Meristem Identity Genes Necessary for the initial induction of the organ identity genes. These genes are the positive regulators of floral organ identity. 10

11. Floral Organ Identity Genes 03 11

12. Floral Organ Identity Genes The genes that determines floral organ identity were discovered as floral homeotic mutants. The homeotic genes that have been cloned, encodes transcription factors—proteins that control the expression of other genes. Most plant homeotic genes belong to a class of related sequences known as MADS box genes. It includes the DEFICIENS gene of snapdragon and the AGAMOUS, PISTILLATA1, and APETALA3 genes of Arabidopsis. The MADS domain enables these transcription factors to bind to DNA for further processing. 12

13. Conti……….. Five different genes are known to specify floral organ identity in Arabidopsis: APETALA1 (AP1), APETALA2 (AP2), APETALA3 (AP3), PISTILLATA (PI), and AGAMOUS (AG) (Bowman et al. 1989; Weigel and Meyerowitz 1994). The organ identity genes initially were identified through mutations that dramatically alter the structure and thus the identity of the floral organs produced in two adjacent whorls. Mutations in the floral organ identity genes dramatically alter the structure of the flower. (A) Wild type; (B) apetala2-2 mutants lack sepals and petals; (C) pistillata2 mutants lack petals and stamens; (D) agamous1 mutants lack both stamens and carpels. (From Bewley et al. 2000.) 13

14. ABCD Model Of Flower Development 04 14

15. ABC Model Of Flower Development The ABC model was articulated in 1991 in a seminal paper by Enrico Coen and Elliot Meyerowitz . The paper was based on the systematic analysis of mutations and the phenotypes produced by double and triple mutants, which proved critical in developing the ABC model. After the genetic analyses in two different species, Antirrhinum majus (Snapdragon) and Arabidopsis thaliana , they proposed that the floral organs have distinct identities , which are specified by a unique combination of homeotic ‘A’, ‘B’ and ‘C’ class of genes activities within each whorl of the flower. This model proposed that A and C components of the model can explain normal organ identity in each whorl. 15

16. Determination of Floral Organ Identity in ABC Model Specifies Sepals Formation of Petals Form Stamens Activity of type A Activities of both A and B Activities of B and C Activity of C Specifies Carpels 16

17. ABCD-MODEL `Description of floral development and their whorls. Factor 1 Factor 2 Identify presence and absence of specific whorl Presence of specific genes effect the presence or absence of whorls. 17

18. ABCDE Model Of Flower Development 05 18

19. ABCDE-Model In this model, class A and E genes are involved in sepal development which is ground state floral organ in first floral whorl. A complex of class A, B and E genes works on petal specification in second whorl. While class B, C and E genes specify third whorl i.e. stamens. Class C and E genes specifies carpels of fourth whorl. . 19

20. ABCDE Model of Flower Development Arabidopsis thaliana showed that these genes encode MADS-box transcription factors. Class A genes encode APETALA2 (AP2). Further studies on Arabidopsis thaliana genome revealed four class E genes, namely, SEPALLATA1 (SEP1), SEP2, SEP3, and SEP4. All four class E genes are partially redundant in function of determining sepals, petals, stamens and carpels. ABCDE model also suggests that AGAMOUS LIKE 6 (AGL6)-clade genes might have role in ovule formation during floral development. 20

21. Refrences https://byjusexamprep.com/liveData/f/2022/3/abc_model_of_floral_organ_development_82.pdf https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_(Boundless)/30%3A_Plant_Form_and_Physiology/30.12%3A_Plant_Development_-_Genetic_Control_of_Flowers https://www.cell.com/current-biology/fulltext/S0960-9822(17)30343-3?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982217303433%3Fshowall%3Dtrue Taiz, L., & Zeiger, E. (2010). Plant Physiology (5th ed.). Sunderland, MA: Sinauer Associates. 21

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