1. Shoot meristem self-organization and identity

2. Vegetative shoot apical meristem (SAM)

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

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

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

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

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

9. (from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))
clavata mutants have enlarged meristems
Wild type clavata3 mutant
clv1 and clv3 mutants look similar
(from J. C. Fletcher et al., Science 283, (1999))

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

11. (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))

12. (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))

13. Model for CLV3 peptide signaling

14. Model for shoot apical meristem (SAM) maintenance
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.

15. Similar regulation in shoot and root meristems
WOX5 is similar in sequence to WUSCHEL.
WOX5 is expressed in the root quiescent center.
Sarkar et al. (2007) Nature 446:

16. Similar regulation in shoot and root meristems
Root cap stem cells differentiate in a wox5 mutant.
Sarkar et al. (2007) Nature 446:

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

18. Shoot meristem identities
Sepals, petals, stamens, carpels
Flower meristems
Inflorescence SAM
Induction of flowering
Leaves,
branches (lateral meristems)
Vegetative SAM

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

20. Vegetative shoot apical meristem (SAM)

21. Flower meristems
Shoot apical meristem (SAM)

22. Flower meristem Flower

23. Arabidopsis flower
Stamen
Gynoecium
(fused carpels)
Petal
Sepal

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

26. 4 sepals 1 2 3 4
4 petals
6 stamens
2 carpels
Whorls

27. Arabidopsis mutants with altered flowers
Wild type
apetala1
cauliflower
apetala1
agamous
pistillata

28. Shoot meristem identities
Sepals, petals, stamens, carpels
Flower meristems
Meristem identity genes (LFY, AP1, CAL)
Inflorescence SAM
Induction of flowering
Leaves,
branches (lateral meristems)
Vegetative SAM

29. leafy mutants:
partial conversion of flowers to lateral branches and leaves

30. leafy mutant flowers have no petals or stamens
Wild type
leafy

31. LEAFY is expressed throughout the flower meristem
(from Weigel et al., 1992, Cell 69: )

32. apetala1 mutant flowers lack sepals and petals and have a new flower where a petal should be
Wild type
apetala1

33. Flowers are converted into leafy shoots in leafy apetala1 mutants

34. Flower meristems behave like inflorescence meristems in the apetala1 cauliflower double mutant
ap1 cal
ap1 cal
Fig

35. Why did they call this mutant cauliflower?
ap1 cal

36. Shoot meristem identities
Sepals, petals, stamens, carpels
Organ identity genes
(AP1, AP2, PI, AP3, AG
SEP1, SEP2, SEP3)
Flower meristems
Inflorescence SAM
Induction of flowering
Leaves,
branches (lateral meristems)
Vegetative SAM