Lecture 19 - Plant homeotic genes Flashcards
(8 cards)
What is plant form?
Plant form is dependent on cell division plan & cell expression
Egg cell (depolarisation
Zygote:
- re-polarisation
- elongation
- asymmetric division
1 - cell:
- symmetric division
- change of division plane
2-4 cell:
- change of division plane
- cell type specification upper/lower tier
Octant:
- change of division plane
- asymmetric division
- cell type specification radial axis
Dermatogen:
- change of division plane
- asymmetric division
- cell type specification hypophysis
- elongation hypophysis
Early-globular:
- change of division plane
- asymmetric division
- cell type specification organizer/stem cells
- cell-cell signalling
Late-globular:
- expansion
- differentiation
- (short) stem cell specification
HEART STAGE
When are stem cells established?
During embryogenesis. The root meristem gives rise to root-derived tissue.
How are organs arranged in plants?
Organs arranged in whorls
Whorl 1 - sepals - green tissue in outer most wall
Whorl 2 - petal
Whorl 3 - stamen - reproductive tissue
Whorl 4 - carpel - reproductive tissue
What are Floral mutants with deletions of the pattern?
Apetala1 - flower consists of just carpels + stamen
Pistillata - sepals & carpels
Agamous - sepals + petals
HOMEOTIC MUTANTS ARE MUTANTS WHERE REPLACEMENT OF ONE PART OF THE PLANT WITH ANOTHER - NO DELETIONS BUT REPLACEMENT
Domains show regions of gene activity - these are NOT morphogen gradients - not morphogens but domains of gene expression & gene regulatory networks
What is the ABC model?
A - apetal1
B - pistillata
C - agamous
As you overlap them, it is clear that the genes expressed in the particular domain, dictate the organ type that forms there
A+B+C
Sepals (A)
Petals (A+B)
Stamen (B+C)
Carpels (C)
Tight domains of expression typically means that negative regulation is often at play (interactions between genes).
A domain & C domain antagonize each other. They prevent each other from spreading into their respective domains.
Removal of A gene (no antagonization of C function) leads to spread of C function spread across all of the walls, due to removal of inhibitory intercation
What are MADS domain Proteins?
Floral homeotic genes are MADS domain proteins.
Drosophila - Homeodomain TFs
Plants - MADS domain TFs
50-60 amino acid DNA binding domain
What mutation is a rose likely to have?
Rose likely to have a C mutant due to lack of carpals.
What is a summary of the ABC model?
Flower has 4 whorls - Sepals/Petals/Stamen/Carpels
A function - Sepals
AB function - Petals
BC function - Stamen
C function - carpel
A function antagonizes C function.
Genes are MADS box transcription factors.
Negative interactions dictate gene expression boundaries
