Basic Introduction to Arabidopsis as a Model organism

1. Arabidopsis: The Model Organism

2. Arabidopsis History
•Member of Mustard Family
•Discovered by Johannes Thal in the 1500s.
•1873 First mutant reported.
•Chromosome number discovered in 1907 by Friedrich Laibach.
•Entire genome sequenced in 2000.

3. What makes Arabidopsis
thaliana a model organism?

4. Short Life Cycle
•48 days from germination to mature seed development.

5. Easy to Grow
Arabidopsis can be grown in small spaces or indoors. They
only require water, soil, and light to reach maturity.

6. Eudicot plant

7. Stamen series from leaf-like to a slender filament.
Morphological series

8. Carpels from leaf-like (conduplicate carpel) to carpels with a highly defined stigma,
style and ovary.

9. Basic “ABC Model of Floral Organ
Development

10. Normal wild-type Arabidopsis thaliana
(Brassicaceae)

11. Arabidopsis
showing 4 floral
organs
Carpels-C
StamensB&C
Petals-A&B
Sepals-A

12. apetala 2 mutant
No A(Ca -St-St - Ca)

13. Apetala mutant No A (Ca -
St-St - Ca)
Wild Type Flower
Ca
Ca
St
St

14. apetala or pistillata mutant, No B
(Se-Se-Ca-Ca)

15. C- Class Mutants
AGAMOUS mutant
No Gametes
(Se-Pe-Pe-Se-Pe-Pe)
Top View
Side View

16. A-Class Mutant
No APETALA 1 or APETALA2
No Petals (only carpels and stamens)
B-Class Mutant
APETALA 3 or PISTILLATA
No petals or a lot of Pistils
The name of a gene describes the flower when that gene is not functional.

17. C- Class Mutants
AGAMOUS mutant
No Gametes
(Se-Pe-Pe-Se-Pe-Pe)
Top View
Side View

18. The SEPALLATA genes alone cannot direct flower development. If you turn on
the SEPALLATA genes in vegetative plants you get petal-like structures where
leaves should be, but none of the other flower parts were present. If you turn
on the ABC genes without SEPALLATA genes, you also do not get a flower. So
BOTH sets of genes are necessary for normal flower development.

19. Flower structure and the “quartet model” of floral organ specification in
Arabidopsis (From Nature 409, 469 - 471 (2001)

20. ABC plus model
Note addition of SEPALLATA
genes and others (green,
blue and black).
Even though it is more
complex-- a gene change
here or there can have a
profound effect on flower
phenotype.
Ancient
Gene

21. Modern Technology
• The arabidopsis genome was sequenced in 2000, and is readily available to the
scientific community.
• Genome is relatively small, compared to other plants.
• Detailed chromosome maps exist for all 5 chromosomes.

22. Technology continued…
• Two major seed stock centers available.
• Easily transformed with Agrobacterium tumefaciens (T-DNA).

23. Acknowledgements
National Science Foundation
TAIR
Dr. Goldberg