1 of 14

GIBBERELLINS PATHWAYS AND SIGNALLING

Presentation by Muhammad Shafiq

March - 2025

GIBBERELLINS PATHWAYS AND SIGNALLING

1

2 of 14

Agenda

Gibberellins Overview

Biosynthesis Pathway

Signalling Mechanism

Receptors and Effects

Growth, Development, and Agriculture

Gibberellin Pathway Disruptions

Future Research Directions

Conclusion and Q&A

GIBBERELLINS PATHWAYS AND SIGNALLING

2

3 of 14

Gibberellins Overview

Gibberellins are plant hormones crucial for growth and development. They influence seed germination, stem elongation, and flowering processes, promoting various physiological responses.

Definition and Functions

GIBBERELLINS PATHWAYS AND SIGNALLING

3

4 of 14

Biosynthesis Pathway

Key enzymes like GA20ox and GA3ox convert geranylgeranyl diphosphate to gibberellins, establishing the hormone's structure in plants.

Precursors such as isoprenoids contribute to gibberellin synthesis, illustrating an intricate network of metabolic reactions.

Biosynthetic Enzymes

Pathway Components

GIBBERELLINS PATHWAYS AND SIGNALLING

4

5 of 14

Gibberellin Biosynthesis Pathway

​

PRESENTATION TITLE

5

Key Points in Regulation

  • Light, temperature, and stress conditions influence enzyme activity in the pathway.
  • The balance between GA biosynthesis and GA degradation controls plant growth stages like seed germination, stem elongation, and flowering.

​

Stage

Key Enzymes

Location

Key Intermediate Compounds

Description

1. Precursor Formation

Geranylgeranyl diphosphate synthase (GGPS)

Plastids (Chloroplasts)

Geranylgeranyl diphosphate (GGPP)

GGPP, derived from the MEP pathway, acts as the starting point for gibberellin biosynthesis.

2. Terpene Cyclization

Ent-copalyl diphosphate synthase (CPS) \nEnt-kaurene synthase (KS)

Plastids

Ent-Kaurene

GGPP is converted to ent-kaurene through cyclization reactions.

3. Oxidation Reactions

Ent-kaurene oxidase (KO) \nEnt-kaurenoic acid oxidase (KAO)

Endoplasmic Reticulum (ER)

Ent-kaurenoic acid → GA12 → GA53

Sequential oxidation reactions convert ent-kaurene into GA12 (a key precursor for active GAs).

4. Formation of Bioactive GAs

GA 20-oxidase (GA20ox) \nGA 3-oxidase (GA3ox)

Cytoplasm

GA9, GA20, GA1 (Active GA)

GA20ox and GA3ox catalyze the conversion of inactive precursors into bioactive gibberellins like GA1 and GA4.

5. Deactivation

GA 2-oxidase (GA2ox)

Cytoplasm

GA8, GA34 (Inactive forms)

GA2ox enzymes degrade bioactive GAs to regulate growth and maintain homeostasis.

6 of 14

GA biosynthesis and endogenous bioactive GA levels in plants.

GA biosynthesis and endogenous bioactive GA levels in plants.

6

In several plants, such as rice and watermelons, GA content is high at the base of the leaf or lower side [10,35]. In addition, several reports also found that bioactive GA content was reduced following the large length of the base to leaves [28]. In these cases, the exact level of GAs was not clear.

Illustration of a schematic plant (right) and GA biosynthesis (left). The arrows are color-coded to correlate with GA forms shown in the biosynthetic pathway. Red arrows indicate the reduced level of GAs due to plant organ position, while black arrows indicate the increased level of GAs. �

7 of 14

Signalling Mechanism

Gibberellins bind to specific receptors, triggering a cascade of intracellular events necessary for gene expression and growth.

Signal Perception

These signals lead to physiological changes such as elongation and germination by regulating downstream target genes.

Cellular Responses

GIBBERELLINS PATHWAYS AND SIGNALLING

7

8 of 14

Receptors and Effects

Gibberellin insensitive dwarf 1 (GID1) receptors play a pivotal role in gibberellin perception.

GID1 Receptors

Influence of gibberellins on processes like seed dormancy and flowering.

Physiological Effects

They control the expression of DELLA proteins, integral to growth and development.

Gene Regulation

GIBBERELLINS PATHWAYS AND SIGNALLING

8

9 of 14

Growth and Development

Gibberellins are key regulators of plant growth, promoting stem elongation, leaf expansion, and flowering. Their role is critical for achieving optimal plant height and development.

Influence on Growth

GIBBERELLINS PATHWAYS AND SIGNALLING

9

10 of 14

Gibberellins in Agriculture

Gibberellins enhance crop yield, improve fruit quality, and regulate flowering in horticulture. They are utilized to promote uniform germination and elongation.

Agricultural Uses

GIBBERELLINS PATHWAYS AND SIGNALLING

10

11 of 14

Gibberellin Pathway Disruptions

Disruptions in gibberellin pathways can lead to stunted growth and poor seed development, impacting agricultural productivity.

Effects of Disruption

Factors such as drought and nutrient availability can affect gibberellin biosynthesis, altering normal plant signaling.

Environmental Stress

GIBBERELLINS PATHWAYS AND SIGNALLING

11

12 of 14

Future Research Directions

Future research may focus on genetic manipulation of gibberellin pathways to enhance stress tolerance and crop yields, exploring their potential applications in sustainable agriculture.

Emerging Areas

GIBBERELLINS PATHWAYS AND SIGNALLING

12

13 of 14

Conclusion

Gibberellins are essential in plant growth and development, with significant applications in agriculture. Understanding their mechanisms provides insights for future advancements.

Key Takeaways

GIBBERELLINS PATHWAYS AND SIGNALLING

13

14 of 14

Q&A Session

This session invites questions and discussions about gibberellins, facilitating a deeper exploration of this essential plant hormone.

Open Floor

GIBBERELLINS PATHWAYS AND SIGNALLING

14