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Transcript
Plant Reproduction - Outline
Plant Reproduction
Floral Development
1. Initiation of flowering
Juvenile to adult growth
2. Pathways leading to flowering
3. Floral morphology
4. Floral meristem and floral organ identity genes… ABC Model
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Initiation of Flowering: Juvenile to Adult Growth
Fig. 41.02(TE Art)
Arabidopsis Transition from Vegetative to
Floral meristems: Morphology
Phase change = competence to respond to other signals
1. Change in leaf morphology
2. Change in leaf arrangement
3. No adventitious roots in adult
1. Phytomeres with elongated internodes
Temperature Light
2. Terminal flower clusters
3. Axillary phytomeres with axillary/terminal flowers
Phase change
Internal developmental changes
Ivy Juvenile
Plant
Ivy Adult
Plant
Adventitious roots
Opposite leaves
No roots
Spiral leaves
Floral promoters,
floral inhibitors
Flowering
1
Control of Juvenile to Adult Phase Change
Elements of Genetic Control – Underexpression of LEAFY gene
1. LEAFY gene of Arabidopsis required for lateral shoots to develop as flowers
2. leafy mutant created in Arabidopsis from methanesulfonate mutagenized seed.
Wild type (LFY)
Æ specifies flowers form
from lateral meristems
Control of Juvenile to Adult Phase Change
Elements of Genetic Control – Overexpression of LEAFY gene
Viral promoter attached to LFY gene then
Inducing juvenile to adult transition. introduced in various plants…
Accelerated
Æ induces juvenile to adult transition.
flowering
LEAFY (LFY) gene required for flowering.
Overexpression of gene required for flowering
LEAFY (LFY) gene in Arabidopsis
Æ required for transition to flower production
Æ overexpressed in plant cells
Æ radically shortens time to flowering
leafy mutant (lfy)
Æ recessive mutation
Æ no flowers
citrus
Wild type
leafy mutant
Schultz, E.A. and G.W. Haughn. 1991. LEAFY, a homeotic gene that regulates inflorescence
development in Arabidopsis. The Plant Cell 3: 771-781.
Genetic Control of Juvenile to Adult Phase Change
Transgenic plant overexpressing LEAFY
gene.
aspen
Developmental Pathway Leading to Flowering
Vegetative to Flowering (adult) phase is suppressed in wild-type plants
EMF gene suppresses flower development
Vegetative meristem
1) flowering is default state
2) inability to flower is the evolved state
Inflorescence meristem
Malformed
flowers
Overcoming genetic repression
Arabidopsis embryonic flower mutation
Æ flowers early
Æ EMF wild-type gene produces protein
to inhibit flowering
Æ emf mutant lacks EMF protein
embryonic flower
mutation in Arabidopsis
Floral meristems
Floral organ identity genes
Flower development
2
Vegetative Shoot Apex
Transition from Vegetative to
Inflorescence and Floral
meristems in Arabidopsis
Developmental/Genetic Pathway Leading to Flowering
Vegetative meristem
1. Vegetative meristem
Inflorescence meristem
Floral meristems
2. Inflorescence and floral
meristems
Reproductive Shoot Apex
Inflorescence
meristem
Floral organ identity genes
A. Larger size
B. Increased frequency of cell ÷ in
central zone
C. Floral meristems form on flanks of
inflorescence meristem
Flower development
Floral
meristems
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FLORICAULA: Floral Meristem identity gene in Snapdragon
Floral Morphology
Stigma
Fig. 41.13(TE Art)
Style
Carpel
Ovary
(carpels =
gynoecium)
Anther
Stamen
Filament
(stamens =
androecium)
Floricaula mutant
Inflorescence, but no flowers
1. Inflorescence meristems
continue to form in bract axils
Wild Type
Petal
(petals = corolla)
Receptacle
Ovule
Sepal
(sepals = calyx)
3
Floral Organs in Arabidopsis
ABC Model of Floral Organ Identity Genes and
Location of their Expression
1. Initiated as whorls (rings)
–
–
–
–
Sepals
Petals
Stamens
Carpels
ACTIVITY TYPES
A = Field or Domain 1
B = Field or Domain 2
C = Field or Domain 3
ABC Model of Floral Organ Identity
A genes: APETALA1*, APETALA2
B genes: APETALA3*, PISTILLATA*
C gene: AGAMOUS*
*Produce MADS box transcription factors.
Floral Organ Identity Genes
Vegetative
Apical
Meristem
Inflorescence
Meristem
Floral
Meristem
Floral
Organs
1. Give floral organs their identity
2. Homeotic genes: Major developmental switches produce transcription factors
3. Some are Cadastral genes – boundary genes that mutually repress each other
Homeotic gene
expression in
Drosophila
Cadastral
genes
4
Homeotic transcription factors
have a MADS domain structure
Homeotic floral organ gene mutations: pistillata2
Homeotic Transcription factor Æ protein
Founding gene family Æ from several species
Yeast
Snapdragons
Arabidopsis
People
MCM1
AGAMOUS
DEFICIENS
SRF
Movie
Wild Type Flower
MADS box genes
1)Highly conserved
2) produce proteins
Æ Homeotic transcription factors
Æ MADS domain structure
pistillata mutant
Carpels not
Stamens
Sepals not
petals
No petals
No stamens
Wild type
MADS box genes
Interpretation of Homeotic mutants with the
ABC model: pistillata mutation
pistillata
mutant
Homeotic floral
organ gene
mutations: agamous
pistillata mutation
B domain gene not functional
1. No stamens
2. No carpels
3. Whorls of petals or sepals
5
Interpretation of Homeotic mutants with the
ABC model: agamous mutation
Quadruple Mutant in Arabidopsis Flowers
What’s the
phenotype of a
ap1, ap2, pi, ag
mutant flower?
agamous mutant
1.No sepals
2.No petals
3.No stamens
4.No carpels
C not functional
Floral Organ Identity Genes
5.All Leaf-like appendages
END Floral Development
1. Give floral organs their identity
•
Determine location at which specific floral organs develop
2. Major developmental switches
•
•
Originally determined through homeotic mutations
Mutations: Floral organs appeared in the wrong place
3. Encode transcription factors
•
Belong to class of related DNA sequences having MADS
box gene domains encode protein structures known as
MADS domains.
4. Three classes: A, B & C
6