Plant Genes and Gene Expression

Metabolic Complexity

Plants are factories:

Photosynthesis → Carbon skeletons and energy → biosynthesis

Complexity in response to the envionment

Plants are sedentary:

• Need to optimize growth to maximize light capture for photosynthesis

• Need to protect against environmental abuses

Light is a key regulator of plant development

Seedings grown in the dark are a lot thinner and larger leaves

Gene Expression

Gene

Transcription → mRNA

Translation → Protein

Examples of Protein Function

• Enzymes

• Electron carriers

• Ion channels

• Structural components

• Receptors

• Transcription factors

Proteins unique to certain species

Ricinus - Richin

Katemfe plant - thaumatin

Do cells differ in their genetic information

No, all cells in an individual have the same genetic information

Carrot totipotency

Shows that any cell in the individual as the genetic information needed to produce the whole plant

Differential gene expression

Only a fraction of the genetic information present in a particular cell is expressed at any one timeC

Constructive gene expression

Expression in all cells all the time (important for housekeeping roles e.g. respiration)

Ways to study gene expression

1. Look at protein - 2-dimensional gel electrophoresis

2. Detect specific mRNAs

   • Transcriptome sequencing - RNA population converted to cDNA copies and sequenced. Use software to monitor abundance of thousands of different transcripts in particular tissues, at different times and in response to various treatments

3. Visualize transcription - Using reporter genes

   • Report genes are easy to assay and are not usually expressed in plants

Hybrid gene fusion

Plant gene contains a promoter and a coding

Promoter contains info for differential transcription

Addition of B-glucuronidase to coding

Assay the hybrid gene fusion in a transgenic plant

Hybrid gene creates Agrobaceterium T-DNA which transforms into a transgenic plant

Spatial regulation of gene expression - CAB

Gene coding major chlorophyll a/b-binding protein (CAB)

Expressed only in chloroplast-containing cells

Addition of B-glucuronidase turns the leaf tissue blue, showing that CAB is only active in the leaves

Environmental Regulation of Gene Expression

1. Light-induced genes - e.g. CAB expression is stimulated by light

2. Stress-induced genes - Certain genes will be expressed in extreme weather (cold, drought ect); certain genes are expressed to help combat the extreme weather, same with parasites

3. Touch-induced genes - Expressed rapidly after mechanical stimulation - touched plants grow shorter