L30 2025 - Plants as Experimental Systems

Page 2: Importance of Plants

Contributions of Plants

• Produce important resources:

  • Food

  • Raw materials

  • Valuable chemicals

  • Oxygen

  • Biofuels

Significance

• Essential for:

  • Feeding the growing global population.

  • Conserving biological resources.

Page 3: Research Necessity

Understanding Plant Growth

• Research is vital to:

  • Improve crop plants.

  • Conserve bioresources.

• A deep understanding of plant growth and development is essential.

Page 4: Experimental Systems

Advantages of Using Plants for Research

1. Ethical Considerations

   • No concerns regarding animal experimentation.

Page 5: Genetic Understanding

Tools for Plant Research

2. Genetic Knowledge

   • For many plants, all relevant genes are known.

   • Accessible tools to study protein functions.

• Example: The Rice Genome project.

Page 6: Plant Cell Potency

Totipotency in Plants

3. Regenerative Abilities

   • Plant cells can regenerate whole plants from single cells in culture via somatic embryogenesis.

   • Exhibit totipotency: ability to develop into any plant structure.

Page 7: Formation Processes

Callus Formation

• Callus cells can differentiate into roots and shoots, essential for plant development.

Page 8: Genetic Modification Techniques

Introducing New Genes

4. Enhancing Genetic Techniques

• Easy to introduce new genes into plants.

Importance

1. Experimental Tools

   • Enables targeted investigations into plant biology.

Page 9: Crop Improvement Objectives

Goals for Genetic Manipulation

2. Enhancing Crop Varieties

• Direct genetic manipulation aims to:

  • Overcome genetic limitations.

  • Introduce novel genes.

Page 10: Specific Crop Improvement Goals

Desired Traits

• Improve crops for:

  • Disease resistance.

  • Stress tolerance (e.g., to cold/drought conditions).

  • Altered harvested product composition.

Page 11: Additional Improvement Goals

• Further aims include:

  • Reducing spoilage of crops.

  • Strengthening previous goals of disease resistance, stress tolerance, and composition enhancement.

Page 12: Reiteration of Goals

Highlighting Improvement Goals

• Emphasizes significance:

  • Disease resistance

  • Stress tolerance (e.g., cold/drought)

  • Quality of harvested product.

Page 13: Genetic Transformation Definition

Direct Introduction of Genes

• Genetic transformation: process of directly introducing new genetic information into plants to create transgenic plants.

Page 14: Mechanism of Gene Introduction

Agrobacterium tumefaciens

• Utilizes a bacterium known for modifying plants genetically.

Page 15: Infection Mechanism

Agrobacterium and Crown Galls

• Infection by Agrobacterium results in "crown galls" (plant tumors characterized by proliferating cells).

Page 16: Characteristics of Agrobacterium

Bacteria Features

• Soil bacterium,

• Motile and swims towards plant wound sites.

Page 17: Genetic Material of Agrobacterium

Ti Plasmid Structure

• Contains chromosomal DNA and T-DNA: the genetic material responsible for inducing tumors.

Page 18: Role of T-DNA

Transfer of Genetic Information

• The T-DNA region on the Ti plasmid is transferred to the plant cell nucleus, initiating transformation.

Page 19: Transformation Process

Agrobacterium and Plant Cell Interaction

• Overview of the transformation process:

  • Agrobacterium interacts with the plant cell.

  • T-DNA enters and integrates into the chromosomal DNA of the host cell.

Page 20: Summary of agrobacterium infection

Steps of T-DNA Integration

1. Agrobacterium enters through wound site.

2. Binds to the plant cell wall.

3. T-DNA is copied from the Ti plasmid and enters the plant cell.

4. Integration of T-DNA into the plant's chromosomal DNA occurs.

Page 21: T-DNA Genes Functions

Functions of Genes on T-DNA

1. Encode enzymes for auxin and cytokinin biosynthesis resulting in tumour formation from abnormal cell division.

2. Encode enzymes for opine biosynthesis, which are utilized by Agrobacterium for growth.

Page 22: Modifying T-DNA

Incorporating Foreign Genes

Process of T-DNA Modification

1. T-DNA starts with opine, cytokinin and auxin

2. Existing genes are deleted and a new gene is inserted

3. a selectable marker gene is introduces alongside the new gene

Page 23: Selectable Marker Functionality

Importance of Selectable Markers

• An antibiotic resistance gene provides a selectable marker

  • it encodes an enzyme that inactivates an antibiotic

• Transformed plants survive in the presence of antibiotic whereas non-transformed plants do not.

Page 24: Transformation Procedure

Steps in Transformation

• Cut tissue placed on culture medium, infected with Agrobacterium, leading to callus formation.

Page 25: Production of Plantlets

Callus Differentiation

• Callus cells differentiate into roots and shoots, screened through antibiotic selection.

Page 26: Culturing Procedures

Finalizing Transgenic Plantlets

• Removal and further culturing of identified transgenic plantlets.

Page 27: Infection Limitations

Challenges in Major Crop Plants

• Agrobacterium does not efficiently infect several of the world’s major crop plants (wheat, maize, rice)

Page 28: Alternative Techniques

Using a Biolistic Gun

• Introduces DNA-coated microscopic metal particles directly into plant tissue, offering an alternative method to Agrobacterium for transformation.

Page 29: Identifying Transformed Cells

Visualization of Transformation

• Cells can be recognised if the new gene encodes an enzyme that produces a coloured product, indicating successful transformation.

Page 30: Regeneration Challenges

Difficulty in Regeneration

• Major crop plants face difficulties in regeneration via culture techniques.

Page 31: Embryo Regeneration Method

Utilizing Embryos for Transformation

• Introduces methods for regeneration from embryos, involving:

  • Generating embryogenic callus and eventual plant regeneration.

Page 32: Conclusion

Summary of Key Points

• The utility of plants for research, vital for feeding the world.

• Gene introduction facilitated by Agrobacterium offers both experimental tools and potential advantages for crop improvement.