meristem organization how do meristems maintain themselves?
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Meristem organization
How do meristems maintain themselves?
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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)
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Vegetative shoot apical meristem (SAM)
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Vegetative SAM
Inflorescence SAM
Flower meristems
Leaves, branches (lateral meristems)
Sepals, petals, stamens, carpels
Induction of flowering
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Inflorescence meristem:
Makes flowers instead of leaves and branches
Stem elongates more
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Flower meristems
Shoot apical meristem (SAM)
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Arabidopsis thaliana: model plant to study development
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Other model plants
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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
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Arabidopsis is closely related to these plants
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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)
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Vegetative shoot apical meristem (SAM)
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(from Long et al., 1996, Nature 379: 66-69)
Wild-type shoot apex shootmeristemless apex
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Gene expression in embryonic SAM
WUSCHEL (WUS) SHOOTMERISTEMLESS (STM)
(from Laux et al., 1998, Cell 95: 805-815)
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wuschel mutant
(from Laux et al., 1998, Cell 95: 805-815)
Wild type
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Gene expression in embryo SAM
WUSCHEL (WUS) SHOOTMERISTEMLESS (STM)
(from Laux et al., 1998, Cell 95: 805-815)
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WUS expression in adult shoot meristems
(from Laux et al., 1998, Cell 95: 805-815)
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(from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))
Wild type clavata3 mutant
clv1 and clv3 mutants look the same
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Expression of CLV1 in Arabidopsis inflorescence shoot meristem
Clark et al., Cell 89: 575-585 (1997)
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CLV3 (A-D) and CLV1 (E) expression
(from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))
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CLV3 expression in a clv1 mutant meristem
(from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))
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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.
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Vegetative SAM
Inflorescence SAM
Flower meristems
Leaves, branches (lateral meristems)
Sepals, petals, stamens, carpels
Induction of flowering
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Vegetative SAM (indeterminate)
Inflorescence SAM (indeterminate)
Flower meristems (determinate)
Leaves, branches (lateral meristems)
Sepals, petals, stamens, carpels
Induction of flowering
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Flower meristems
Shoot apical meristem (SAM)
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Arabidopsis flower
sepal
stamen
carpelpetal