1. Meristem organization
How do meristems maintain themselves?

4. 0d d d d
Effect of ablation of quiescent center (QC) on tissue-specific marker gene expression
(from Sabatini et al., 1999, Cell 99: )

5. Vegetative shoot apical meristem (SAM)

7. Sepals, petals, stamens, carpels
Flower meristems
Inflorescence SAM
Induction of flowering
Leaves,
branches (lateral meristems)
Vegetative SAM

8. Inflorescence meristem:
Makes flowers instead of leaves and branches
Stem elongates more

9. Flower meristems
Shoot apical meristem (SAM)

10. Arabidopsis thaliana: model plant to study development

11. Other model plants

12. Arabidopsis thaliana (Mouse-ear cress, Thale cress)
Small weed, related to mustard - can fit thousands of plants in a small growth room
Short generation time: 6-8 weeks
Diploid, self-pollinating, transformable
Small sequenced genome: About 125 Mb and 25,000 genes

13. Arabidopsis is closely related to these plants

14. 3. Screen M2 plants for mutants having phenotypes of interest
Finding Arabidopsis mutants
1. Mutagenize seeds (M1)
EMS
(ethylmethane
sulfonate)
2. Grow M1 plants (let self-fertilize and collect M2 seed)
3. Screen M2 plants for mutants having phenotypes of interest

15. Vegetative shoot apical meristem (SAM)

16. Wild-type shoot apex shootmeristemless apex
(from Long et al., 1996, Nature 379: 66-69)

17. Gene expression in embryonic SAM
WUSCHEL (WUS) SHOOTMERISTEMLESS (STM)
(from Laux et al., 1998, Cell 95: )

18. Wild type
wuschel mutant
(from Laux et al., 1998, Cell 95: )

19. Gene expression in embryo SAM
WUSCHEL (WUS) SHOOTMERISTEMLESS (STM)
(from Laux et al., 1998, Cell 95: )

20. WUS expression in adult shoot meristems
(from Laux et al., 1998, Cell 95: )

21. (from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))
Wild type clavata3 mutant
clv1 and clv3 mutants look the same
(from J. C. Fletcher et al., Science 283, (1999))

22. Expression of CLV1 in Arabidopsis inflorescence shoot meristem
Clark et al., Cell 89: (1997)

23. (from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))
CLV3 (A-D) and CLV1 (E) expression
(from J. C. Fletcher et al., Science 283, (1999))

24. (from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))
CLV3 expression in a clv1 mutant meristem
(from J. C. Fletcher et al., Science 283, (1999))

26. Support for model:
In clv mutant, WUS expression domain expands.
clv wus double mutants resemble wus single mutants.
If you overexpress WUS, CLV genes are activated and new meristems form.

27. Sepals, petals, stamens, carpels
Flower meristems
Inflorescence SAM
Induction of flowering
Leaves,
branches (lateral meristems)
Vegetative SAM

28. Sepals, petals, stamens, carpels
Flower meristems (determinate)
Inflorescence SAM (indeterminate)
Induction of flowering
Leaves,
branches (lateral meristems)
Vegetative SAM (indeterminate)

29. Flower meristems
Shoot apical meristem (SAM)

30. Arabidopsis flower
stamen
carpel
petal
sepal