slide1 l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Spring 2008 BIO 350M/388M Molecular mechanisms of flowering PowerPoint Presentation
Download Presentation
Spring 2008 BIO 350M/388M Molecular mechanisms of flowering

Loading in 2 Seconds...

play fullscreen
1 / 41

Spring 2008 BIO 350M/388M Molecular mechanisms of flowering - PowerPoint PPT Presentation


  • 360 Views
  • Uploaded on

Spring 2008 BIO 350M/388M Molecular mechanisms of flowering Sibum Sung Section of Molecular Cell & Developmental Biology University of Texas at Austin When to flower is a matter of the survival of species Floral transition (Aukerman and Amasino, 1998)

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Spring 2008 BIO 350M/388M Molecular mechanisms of flowering' - Ava


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Spring 2008 BIO 350M/388M

Molecular mechanisms of flowering

Sibum Sung

Section of Molecular Cell & Developmental Biology

University of Texas at Austin

slide3

Floral transition

(Aukerman and Amasino, 1998)

Transition in developmental programs: from vegetative growth to reproduction

slide6

“Maryland Mammoth” cultivar of tobacco requires Short Days for flowering (Allard & Garner, 1918)

Green house grown (kept as Long Days) “Maryland Mammoth” plant does not flower

slide7

Floral induction of leaves of Short Day plant Perrila crispa

“Something” must be produced in leaves and “move” to the meristem

Long journey to identify “Florigen” began

(Lang and Zeevart)

slide8

Concept of Florigen (flowering hormone)

A substance made in leaves which induces the shoot to flower, and it is “graft-transmissible”

Only problem is “No one could ever isolate or purify such a substance (and many tried!)”.

“Florigen” remained a hypothesis for decades until……

slide9

Genetics came to the rescue

Arabidopsis: Long Day Plant

Flowering is induced by Long Day (LD)

Certain late flowering mutants are blind to photoperiod

i.e) contstans (co),

flowering locus t (ft)

CO: transcriptional co-activator

FT: transcriptional co-activator (?)

slide10

Inductive

Photoperiod

CO

FT (and other floral integrators)

Floral Transition

slide11

How plants (and other organisms) measure the length of day and night ?

External coincidence model:

(originally proposed by Boenning, 1936)

Light has a dual role in this model:

- entrains the circadian oscillation of light- and dark-sensitive phases

- directly required for the production of the signal.

slide13

Photoperiod-dependent activation of FT is explained by the external coincidence model

CO mRNA is circadian regulated.

CO protein is not stable in dark in Arabidopsis

slide14

FT is a floral activator both in LD and SD plants

Long Day Plant

Short Day Plant

(Kobayashi & Weigel, 2007)

CO in Long Day plants and similar proteins in Short Day plants are regulated in opposite ways

slide15

FT is Florigen! ? (at least a part of it)

In Arabidopsis (top), a leaf protein moves from a flowering graft into a nonflowering mutant, causing a stem and blossoms to form (Corbesier et al., 2007).

In rice (bottom), the equivalent protein (green) shows up in the shoot apical meristem (Tamaki et al., 2007)

Of course, FT protein may move with other substances.

Stay tuned, since Florigen has a long history of misleading scientists

slide16

Regulation of floral induction

Besides the photoperiod-dependent regulation, floral transition is under controls of many other cues.

(Kobayashi & Weigel, 2007)

slide17

Some plants need winter to flower

Vernalization

Acquisition of the competence to flower in the spring by exposure to the prolonged cold of winter (Chouard, 1960).

slide18

Memory of winter can be mitotically stable

From Lang & Melchers memory in Hyocyamus niger

slide19

Intron I

Vernalization Requirement: Natural Variation

(Klaus Napp-Zinn)

Suppression of FLC acts via Region A of Intron I

Region A

pIDA

FLC in Col-flc

pIDA in Col-flc

(pIDA responds to vernalization)

slide20

FLC (FLOWERING LOCUS C)

is a potent repressor of flowering

Inductive

Photoperiod

CO

FT (and other floral integrators)

Floral Transition

FLC

slide27

Genetic screening

for vernalization insensitive (vin) mutants

  • VRN2: Homolog of Su(z)12 (Gendall et al., 2001)
  • VRN1: Myb DNA binding protein (Levy et al., 2002)
  • VIN3: PHD finger protein (Sung & Amasino, 2004)
  • LHP1: LIKE-HETEROCHROMATIN PROTEIN (Sung et al., 2006)
  • VIL1: PHD finger protein (Sung et al., 2006; Greb et al., 2007)
  • VIN5: Histone arginine methyl transferase (Sung, Schmitz, Amasino, 2008)
  • VIN7: PAH2 domain protein (Sung, Schmitz, Amasino, unpub)
  • ; Genes are involved in the regulation of chromatin structure
slide28

Nucleosome core particle

(Luger et al., 1997)

slide29

Modifications of nucleosomes

(Turner, 2005)

  • Charged amino acid residues on the exposed face of histone proteins can be covalently modified
slide30

Histone code

Active chromatin (ON)

Repressed chromatin (OFF)

High in:

H3K9Me, H3K27Me

High in:

Acetylation, H3K4Me, H3S10P

Modified histone could be recognized by activation/repression complexes and establish stable activation/repression chromatin

(Jenuwein and Allis, 2001)

slide32

Dynamics of FLC chromatin

Active FLC Chromatin

High in

Ac; H3K4Me; H3S10P

H2A.Z Histone variant

Repressed FLC Chromatin

High in

H3K9Me; H3K27Me

H4R3MeS2; LHP1

VIL1, VIN5

VIN3, VIL1, VIN5 VRN2, VRN1, etc.

(from Sung and Amasino, 2005)

slide33

Environmentally induced chromatin changes

ON; Fall

VIL1, VIN5

VIN3, VIL1, VIN5 VRN2, VRN1, etc.

WINTER!

OFF; Spring

(from Sung and Amasino, 2005)

slide34

FLC (FLOWERING LOCUS C)

is a potent repressor of flowering

Inductive

Photoperiod

CO

FT (and other floral integrators)

Floral Transition

FLC

slide35

Stable repression of FLC provides competence to flower upon inductive photoperiod

Inductive

Photoperiod

CO

FT (and other floral integrators)

Floral Transition

FLC

slide36

Molecular basis of the vernalization response

  • FLC is a potent repressor of flowering.
  • Competence: in Arabidopsis, largely a function of FLC expression level. Vernalization leads to competence via repression of FLC.
  • Mitotic stability: Vernalization-mediated repression of FLC via histone modifications that are hallmarks of epigenetic silencing
slide37

Fall: flowering repressed

FLC is highly expressed and thus represses FT activation

Short Days prevents CO-FT activation

slide39

Stable repression of FLC by chromatin changes eliminates antagonistic effect on FT activation

  • Long Days promote CO-FT activation
slide40

FLC

resetting

  • During meiosis, FLC is reactivated
  • (reversing chromatin structure)
slide41

Multiple flowering control pathways

Many genes have variations even within same species

; provide flexibilities to adapt to local environments