1

How Genes Impact Plant Propagation

David G. ClarkUF Environmental Horticulture

Genes

• Provide the physical mechanism for reproduction of traits

• Provide information for controlling expression of traits

Pre-Mendel

• Accounting for species diversity

• Carolus Linnaeus –(17th C.) systematic hierarchy for classifying living things (taxonomy)

2

Pre-Mendel

• Species Diversity• Charles Darwin –

Origin of Species(1859)

• Theory of evolution, survival of the fittest, adaptive change

• Visual inspection and Mass Selection

Then came Mendel…

Mendelian Geneticsmarked the start of an era in which selection became based on hereditary principles

Predictability

Mendelian Genetics

• How are traits passed from one generation to the next?

• Mendel (1866) -Experiments in Plant Hybridization - was the first to relate the outward appearance of an organism (phenotype) to its inner genetic constitution (genotype)

3

Mendelian Genetics

Mendel’s Garden - 2001

Brno, Czech Republic

Mendelian Genetics & Beyond

• Where are genes located?

• Thomas Hunt Morgan (1910) – Drosophila(fruit flies), linkage and chromosomes

4

Mendelian Genetics & Beyond

• What is the job of the gene?

• George Beadle (1940)One gene one enzyme hypothesis

• Neurosporamutations

Mendelian Genetics & Beyond

• What molecule is the genetic material?

• Oswald Avery (1941) –work on bacteria proved that genes were made of DNA

Mendelian Genetics & Beyond

• What molecule is the genetic material?

• Alfred Hershey (1952) – The Blender Experiment proved that DNA is the molecule of heredity

5

DNA-based Genetics

• What is the structure of a DNA molecule?

• Watson and Crick

• DNA structure = function

DNA-based Genetics

• Lots of people helped Watson and Crick

Pauling

Chargaff

Wilkins & Franklin

DNA-based Genetics

• April 2, 1953 -Watson and Crick –Published a paper in Nature solving the structure of DNA

• This structure was the key to unlocking the technology of life

• It is perhaps the most important biological discovery of the 20th

century – this was the start of the biotechnology era

6

Watson and Crick’s Double Helix

Implications of Watson & Crick

• DNA embodied the organizing thesis of molecular biology

• Understanding the structure of a molecule gives clues to its biological function

After Watson & Crick

• Francis Crick (1957) – laid the intellectual framework to guide the cracking of the genetic code

• Sequence hypothesis– DNA sequence and protein sequence are co-linear

• Central Dogma – Information stored in DNA flows through RNA to proteins

7

After Watson & Crick

After Watson & Crick

After Watson & Crick

• Cracking the Genetic Code

Holley Khorana Nirenberg

8

The Genetic Code

What is a gene?

What is a gene?

9

Regulation of Genes

• Cell differentiation is a function of regulated gene expression

• Plant cells are totipotent–every cell has the genetic potential

to regenerate into a fully differentiated plant

How do different cell types occur?

• Not all genes are active in all cells at all times

• Gene expression – regulated by development and environment– Controlled at many levels

Regulation of genes

10

Regulation of genes

After Watson & Crick

Coordinating Gene Expression

• Gene Promoters – regulatory elements that function in recruiting proteins that facilitate transcription

• Cis-acting DNA elements–Act on the same DNA strand as the

gene being regulated

11

Coordinating Gene Expression

• Transcription factors – DNA binding proteins that interact with promoters and RNA polymerase

• Trans-acting factors–Bind DNA and other proteins

Coordinating Transcription

DNA Transcription

• Occurs mainly in the nucleus• Synthesis of RNA on the DNA

template– A primary control step in regulation of

gene expression• All RNAs are transcribed by RNA

polymerase– Copies DNA sequence into RNA

sequence

12

DNA Transcription• Occurs mainly in the nucleus

DNA & RNA

RNA Polymerase

• Copies DNA sequence into RNA sequence

13

RNA

• Primary product of gene expression – single stranded

• Decodes DNA info into proteins• 3 types of RNA:

– rRNA - platform– tRNA - adapter– mRNA - messenger

Ribosomal RNA (rRNA)

• The bulk of cellular RNA

• Ribosome - A platform for reading mRNAs

Transfer RNA (tRNA)• Adapters – bind mRNA & amino acids

14

Messenger RNA (mRNA)

• Encode amino acid sequences of proteins

Protein synthesis - Translation• Occurs mainly in the cytoplasm

Protein synthesis - Translation

15

Why is this important?

• Enzymes are proteins• Enzymes catalyze biochemical

reactions• Biochemical reactions determine

how plants respond to external and internal stimuli

Biotechnology

• How we actually use all of this knowledge to make a difference

• Cell and Tissue Culture• DNA Marker technology• Recombinant DNA technology

Cell and Tissue Culture

• Micropropagation - aseptic

16

DNA Marker Technology

• DNA Fingerprinting

Recombinant DNA Technology• Cloning

Recombinant DNA Technology• Transgenic Plants

17

Genomics – The Future

Functional Genomics

We can now look at expression of thousands of genes at a time

Bright Futures

• We are just now seeing the tip of the iceberg in plant biotechnology

• The next decade will prove to be a time of biotechnology applications to new crops

• We need to know how to efficiently propagate new biotech plants:sexually and asexually

18

Propagators will make a difference!