Meristem organization

How do meristems maintain themselves?

0d 1d 3d 5d

Effect of ablation of quiescent center (QC) on tissue-specific marker gene expression

(from Sabatini et al., 1999, Cell 99: 463-472)

Vegetative shoot apical meristem (SAM)

Vegetative SAM

Inflorescence SAM

Flower meristems

Leaves, branches (lateral meristems)

Sepals, petals, stamens, carpels

Induction of flowering

Inflorescence meristem:

Makes flowers instead of leaves and branches

Stem elongates more

Flower meristems

Shoot apical meristem (SAM)

Arabidopsis thaliana: model plant to study development

Other model plants

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

Arabidopsis is closely related to these plants

Finding Arabidopsis mutants

EMS (ethylmethane

sulfonate)

3. Screen M2 plants for mutants having

phenotypes of interest

2. Grow M1 plants (let self-fertilize and collect M2 seed)

1. Mutagenize seeds (M1)

Vegetative shoot apical meristem (SAM)

(from Long et al., 1996, Nature 379: 66-69)

Wild-type shoot apex shootmeristemless apex

Gene expression in embryonic SAM

WUSCHEL (WUS) SHOOTMERISTEMLESS (STM)

(from Laux et al., 1998, Cell 95: 805-815)

wuschel mutant

(from Laux et al., 1998, Cell 95: 805-815)

Wild type

Gene expression in embryo SAM

WUSCHEL (WUS) SHOOTMERISTEMLESS (STM)

(from Laux et al., 1998, Cell 95: 805-815)

WUS expression in adult shoot meristems

(from Laux et al., 1998, Cell 95: 805-815)

(from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))

Wild type clavata3 mutant

clv1 and clv3 mutants look the same

Expression of CLV1 in Arabidopsis inflorescence shoot meristem

Clark et al., Cell 89: 575-585 (1997)

CLV3 (A-D) and CLV1 (E) expression

(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, 1911 -1914 (1999))

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.

Vegetative SAM

Inflorescence SAM

Flower meristems

Leaves, branches (lateral meristems)

Sepals, petals, stamens, carpels

Induction of flowering

Vegetative SAM (indeterminate)

Inflorescence SAM (indeterminate)

Flower meristems (determinate)

Leaves, branches (lateral meristems)

Sepals, petals, stamens, carpels

Induction of flowering

Flower meristems

Shoot apical meristem (SAM)

Arabidopsis flower

sepal

stamen

carpelpetal