Leaf Development And Evolution II: Polarity, Boundaries And Axes Flashcards
Phyllotactic patterns in angiosperms
1) alternate
2) opposite
3) whorled
4) spiral
Spiral phyllotaxy in seed plants under SEM
- dome = S.A.
- protrusions = leaves
- pattern is shrinking
Phytomers
1) leaf
2) axillary bud
3) internode
- iterative development
- specific arrangement
Monocot phytomer
- leaf blade @ top
- different order
S. kraussania
- dichotomous branching: specifically patterned major and minor branches
- ventral and dorsal leaf pairs w/ specific rhizophores
S. kraussania shoot patterning
- how to generate 6/8 leaves?
- 2 cells on A surface act as stem cells
- meristem bifurcates
- 4x growth axes; DV, LR, 2x diagonal
LR S. kraussania
How does meristem bifurcate?
Fern shoot development
1) tetrahedral shoot initial
2) frond initial
3) pinna initial
Older primordia specify leaf position
- anatomically distinguishable from S.A. flanks
- isolate I1 from apex by incision
- I3 develops closer to I2 than usual
- mechanical constraint? Biochemistry? Combinatorial?
abphyll
2x P3 leaves
NPA
- auxin analog
- binds to PATs and doesn’t detach
Leaf initiation under NPA
- SAM becomes pin-shaped
- no leaf initiation from flanks
pin1
- SAM becomes pin-shaped
- no leaf initiation from flanks
- auxin: rescue
- lanolin control
Auxin:
- IAAH, IAA- (protonation states)
- cell wall/apoplast (5.5): IAAH
- diffuses through lipid bilayer to enter cytoplasm
- cytoplasm (7): IAA-
- stuck!
PIN polarity creates
Auxin I1 maxima
PIN polarity aligns w
- microtubule orientation
- stress, for support
Ablating stressed cells with a laser
PIN moves away
Leaf axes
1) proximo-distal
2) medio-lateral
What determines axes in a leaf?
- when a leaf is developing, axes info comes from the shoot
- once a leaf is specified, it is all there
Explant P1
- develops as a leaf
Explant I1 and I2
Develop as shoots
Remove all leaves
I1 develops as leaf
Features of adaxial-abaxial leaf axis
- stomata (abaxial abundance)
- xylem (adaxial)
- phloem (abaxial)
- adaxial faces towards meristem
- abaxial faces away
PHABULOSA and KANADI
2x important TFs for adaxial-abaxial specification
recessive kanadi triple KO: kan1-2, 2-3, 3-1
- adaxialised
recessive phabulosa triple KO: rev-9, phb-6, phv-5
- abaxialised
- ## phloem encircles xylem
REVOLUTA, PHABULOSA, PHAVOLUTA
Class III HD-ZIP family
dominant phabulosa
Adaxialised?
PHB primordial expression by in situ hybridisation
- detect gene transcript thru colourimetric reaction
- P2: ubiquitous
- P6: adaxialised
PHB regulation
- PHB mRNA: adaxial
- miRNA165/166: abaxial
- dominant phb mRNA: ubiquitous because miRNA can no longer bind
KANADI
induce GARP TFs
KANADI expression
- transverse and longitudinal sections of v young leaves
- abaxialisation
stm1
- no SAM
- KNOX LOF
cuc1, cuc2
- no SAM
- fused cotyledons
- NAC domain TFs
STM and CUC2 expression
- STM repressed in cuc1, cuc2
- CUC2 similar expression to wt in stm
STM and CUC feedback regulatory loop
- STM defines meristematic region
- STM prevents CUC localisation
- CUC defines borders of meristematic region
- need both in a functioning meristem
wox
- narrow leaf phenotype
- lamina don’t expand @ base
wox3
- thin blade
- does not establish marginal region
- no KNOX in SAM
How is the margin defined?
Suppression of KNOX accumulation
WOX
- WUS-like
- expands leaf
- defines middle of adaxial-abaxial axis
WOX mechanism
- promotes auxin biosynthesis @ leaf margins ; growth agonist
- increased expression at base; higher growth rate
- decreased expression at tip; higher differ mention
