L31 2025 - Plant Genes and Gene Expression

Page 2: Complexity of Plants

• Plants are remarkably complex organisms due to:

  • Metabolism

  • Development

  • Responses to the environment

Page 3: Metabolic Complexity

• Plants act as factories:

  • Involved in various metabolic processes.

  • Key processes:

    • Photosynthesis for carbon skeletons and energy production

    • Other biosynthetic pathways contributing to plant metabolism

• photosynthesis → carbon skeletons and energy → biosynthesis

Page 4: Developmental Complexity

• Developmental Process in Plants:

  • Example discussed: How do plants create flowers?

  • Reference example: Paphiopedilum from Orchidaceae family.

Page 5: Environmental Responses

• Response to Environmental Challenges:

  • Need to optimize growth for effective light capture essential for photosynthesis

  • Requirement to defend against various environmental stresses

  • Notable points:

    • Plants are sedentary and must cope with environmental stresses effectively.

Page 6: Role of Light

• Light as a Key Regulator:

  • Light markedly affects plant development

  • Comparison of seedlings grown in darkness vs. light.

Page 7: Environmental Stressors

• Diverse Environmental Stresses:

  • Plants face various stressors:

    • Frost

    • Pathogenesis

    • Salinity

    • Drought

Page 8: Genetic Information and Complexity

• Genes and their Products:

  • Genetic information is essential to maintaining complexity in traits and characteristics.

  • Importance of genes encoding for proteins.

Page 9: Gene Expression Overview

• Basic Concept of Gene Expression:

  • Process involves:

    • Transcription: DNA is transcribed to mRNA

    • Translation: mRNA is translated to proteins

Page 10: Protein Functions

• Variety of Protein Functions:

  • Examples of proteins:

    • Enzymes, electron carriers, ion channels, structural components, receptors, transcription factors

  • Average plant contains 35-40,000 different proteins

Page 11: Protein Conservation and Uniqueness

• Protein Variation Among Species:

  • Some proteins conserved across species (e.g. ricin, thaumatin)

  • Others are unique to specific species (e.g. Katemfe plant Ricinus).

Page 12: Cellular Functionality

• Cellular Diversity in Protein Composition:

  • Different cells (flower, leaf, root, stem) show varying complement of proteins necessary for their specific functions.

Page 13: Consistency of Genetic Information

• Genetic Consistency Across Cells:

  • All cells in an individual plant carry the same genetic information.

  • Different protein expressions account for functional diversity.

Page 14: Carrot Totipotency Experiment

• Demonstration of Totipotency:

  • Carrot experiment shows any cell can produce a whole plant.

  • References: Campbell Fig 20.16 illustrating totipotency.

Page 15: Differential Gene Expression

• Expression Patterns:

  • Only a fraction of genetic information in cells is expressed at any time.

  • Differential Gene Expression: Variation in expression levels among genes

  • Constitutive Gene Expression: Genes expressed in all cells continuously.

Page 16: Gene Variability

• Variability in Higher Plant Genes:

  • Average higher plant has about 25,000 to 30,000 genes

  • Genes exhibit differential expression:

    • Spatially (where)

    • Temporally (when)

    • Environmentally (condition)

Page 17: Understanding Gene Functionality

• Importance of Gene Function Discovery:

  • To understand growth and development, identifying gene functions and expression control is critical.

Page 18: Techniques to Study Gene Expression

• Methods to Analyze Gene Expression:

  1. Look at proteins

  2. Analyze specific mRNAs

• Using 2-D gel electrophoresis for analysis.

Page 19: Transcriptome Sequencing

• RNA Sequencing Methods:

  • Convert RNA populations to cDNA, then sequence.

  • Software can monitor transcript abundance in various tissues and conditions.

Page 20: Reporter Genes

• Visualizing Gene Expression:

  • Reporter genes:

    • Easy to assay, typically not expressed in plants

    • Example: Bacterial b-glucuronidase producing a color change.

Page 21: Hybrid Gene Fusion Technique

• Creating Hybrid Genes:

  • Fusion of promoter from plant gene with coding for b-glucuronidase allows assay of expression patterns.

Page 22: Transgenic Plant Assays

• Assaying Hybrid Gene Expression:

  • Transformation using Agrobacterium T-DNA into a transgenic plant

  • Expression pattern of b-glucuronidase is promoter-dependent.

Page 23: Spatial Regulation Example

• Example of Spatial Gene Regulation:

  • Gene encoding chlorophyll a/b-binding protein (CAB) is expressed in chloroplast-containing cells only.

Page 24: Experimental Fusion and Assay

• CAB Gene Assay in Transgenic Plants:

  • Hybrid gene experiment shows expression specificity in chlorophyll-containing leaf tissues.

Page 25: Expression Specificity Results

• Observations from Experiments:

  • b-glucuronidase expression observed only in leaves, confirming CAB promoter activity.

Page 26: Environmental Gene Regulation

• Light-Induced Gene Expression:

  • Example: CAB gene expression stimulated by light exposure

  • Differential expression based on environmental conditions (dark vs. light).

Page 27: Stress-Induced Genes

• Genes Responsive to Stressors:

  • Genes that are activated during stressful conditions such as:

    • Cold

    • Pathogenesis

    • Drought

Page 28: Touch-Induced Gene Regulation

• Genes Responsive to Mechanical Stimulation:

  • Expression patterns that change following physical touch, demonstrating adaptive response.

Page 29: Summary of Learning Points

• Key Points on Gene Expression:

  • Genes are expressed differentially to enable adaptive responses to stimuli for survival.

  • Various methods available for studying differential gene expression.