SHATTERPROOF MADSbox genes control seed dispersal in Arabidopsis

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SHATTERPROOF MADS-box genes control seed
dispersal in Arabidopsis
Liljegren SJ, Ditta GS, Eshed HY, et al. Nature
404, 766-770 (2000)
Presented by Sajee and Wintai
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Floral Development
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ABC Model of Floral Development
C gene expression
B gene expression
A gene expression
Sepals Petals Carpels stamens
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MADS-box genes
Family of transcription regulator
genes Conserved in yeast, plants, human 17
genes in plants-floral architecture The MADS box
gene involved in diverse aspects of plant
development, extensive redundancy between family
members.
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Objectives

• Identification of the roles of SHP1 and SHP2 in
  pod shattering of Arabidopsis
• Phenotypic differences between shp1 shp2 double
  mutant and wild-type
• Monitoring cell differentiation in valve cell of
  shp1 shp2 and wild type
• Over expression of SHP1 and SHP2 to see whether
  they alter the fate of valve cells into valve
  margin

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Arabidopsis fruit structure and pod shatter

• Wild-type gynoecium at fertilization
• Dry fruit during dehiscence

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Proposed factors contributing to fruit dehiscence
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Sence et al. J. of Microscopy (1996)
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SHP1 and SHP2
Member of MADS box gene family (AGL1 and AGL5)
SHP1 and SHP2 are expressed in developing
gynoecium before the valve margin is distinct
and continue expressed until after fertilization
SHP1 and SHP2 may function in specifying the
valve margin and direction of dehiscence zone
development in mature fruit
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Homologous recombination disrupted SHP2 (AGL5)
gene in Arabidopsis
Kempin et al. Nature (1997)
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Identification of shp1 mutant by T-DNA insertion
mutagenesis
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5,600 T-DNA insertional lines were
screened. T-DNA insertion occurred in the large
first intron of SHP1 locus.
What is the evidence that shp1-1 is a null
mutant?
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Double mutant shp1 shp2 was constructed and
identified
To construct shp1 shp2 double mutants, the shp1-1
mutant was crossed to the shp2-1 single mutants.
F2 progeny were screened by PCR using combination
of primers.
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Phenotypic differences between the valve margins
of shp1 shp2 and wild-type fruit
dz dehiscence zones
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SHP1 and SHP2 promote valve margin lignification
vm valve margin Iv internal valve cell
layer vb vascular bundles
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Cellular differentiation of WT and shp-1 shp-2
valve margins.
Valve Cells
Valve Margin Cells
Dehiscence zone cells
Lignified cells
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Monitoring Cellular Differentiation of shp1 shp2
and Wt
shp1 shp2 x GT 140
shp1 shp2 x YJ 36
F1
F1
F2
F2
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SHP1 and SHP2 regulate the expression of valve
margin molecular markers
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Overexpression Experiments
No margins
Loss of function alleles
Overexpression
No valves???
SHP1
35S
Coding region
SHP2
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Cellular Differentiation of 35SSHP1 35SSHP2
Transgenic plants
35SSHP1 35SSHP2 x GT 140
F1 (x)
F2
35SSHP1 35SSHP2 x YJ 36
F1 (x)
F2
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Conclusion
1. Both SHP1 and SHP2 are essential for valve
margin differentiation (formation of dehiscence
zone and lignification of adjacent cells) 2.
Gain of function experiment show that neither
SHP1 nor SHP2 alone is sufficient in converting
valve cells to valve margin cells 3. GT140 is
downstream of SHP1 and SHP2
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Why did they have to screen for more shp1 and
shp2 alleles?
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AGL11, SHP1 and SHP2 are expressed in ovules.
How would you test whether these three AGL genes
regulate ovule development? Forward
genetics Reverse genetics