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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

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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

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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

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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

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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)

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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

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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

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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

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