Leaf Development And Evolution I: What Is A Leaf Flashcards
1
Q
Leaf function
A
1) support
2) photosynthesis
3) defence
4) bearing spores
5) nutrition
6) floatation
2
Q
Monocot grass leaf
A
- blade, ligule, sheath
3
Q
Eudicot simple leaf
A
Blade, petiole
4
Q
Seed leaves
A
Cotyledons
5
Q
Reduced leaves
A
- cactus spines
- butcher’s broom cladode
- whisk fern
6
Q
What is an angiosperm leaf?
A
- determinate lateral organ associated with a bud
7
Q
SAMs
A
- make leaves
- transition from indeterminate to determinate growth via leaf primordia
8
Q
SAM zones
A
1) central
2) peripheral
3) rib
9
Q
SAM Layers
A
1) L1 (outer)
2) L2 (sub-surface)
3) L3 (inner)
10
Q
SAM function
A
- perpetuate stem cell pop
- produce organ dedicates
11
Q
Perturbed SAM mutants
A
- wuschel
- clavata1, 2, 3
12
Q
Wuschel
A
Homeodomain protein Responsible for proliferating cells
13
Q
wuschel
A
- defective (reduced) meristem forms defective organs
- can form axillary meristems
- decreased CLV; less cells in central zone
14
Q
clavata1, 2, 3
A
- enlarged meristem
- more cells in central zone
15
Q
CLAVATA1, 2, 3
A
Component of receptor-ligand pathway that makes less cells in central zone
16
Q
WUS/CLV interactions
A
- WUS promotes CLV expression
- CLV inhibits WUS zone
- feedback inhibition
17
Q
CLV OX
A
~ wus (due to strong inhibition)
18
Q
Expression doesn’t always mean function
A
Just because the transcript is there, doesn’t mean the protein is
19
Q
Stem cell maintenance
A
- kept beneath stem cell zone
- easy to self-regulate upon environmental cue
- WUS = essential for stem cell identity
20
Q
Periclinal chimaeras
A
- one layer has a different identity
- generated by grafting
- helps you work out what contributions each layer makes to final structure
- reveal contributions of SAM layers to leaves
21
Q
Sectorial chimaeras
A
- for clonal (sector) analysis
- deduce what part of the meristem does what
- reveals no. of leaf founder cells
- shows plastochron
22
Q
Sector induction to determine cell lineage relationships
A
- in tobacco
- genetic stock: mid-green double heterozygote
- double chance of sector
- one break = green
- one break = yellow
23
Q
Lineage analysis
A
- pattern of division at each plastochrons
- division continues at leaf base
24
Q
Leaf initiation in tobacco
A
- 120-180 founder cells (15x2-3x4 in a dome)
- L1, 2 and 3 maintained
- requires co-ordination
25
L1
Upper and lower epidermis
26
L2
Palisade upper mesophyll
27
L3
Inner mesophyll
Vascular tissue
28
KNOX genes
- knotted1-like homeobox
- Homeodomain proteins bind DNA
- green algae and land plants
29
Ectopic cell division in KNOX GOF
- 35S constitutive for expression
- necessary and sufficient
30
Simple angiosperms
Maize, antirrhinum, arabidopsis, pea, tobacco
31
Simple leaf formation in angiosperms
- KNOX turns off in primordium
- what turns it off?
- need recessive LOF
32
rs2
- -ve Kn1 regulator (transverse visualisation)
- rough sheath 2
- similar to kn1-0
- ectopic Kn1 accumulation in leaf primordium
33
RS2 and Kn1
Expressed in mutually exclusive domains / zones
34
ASl
- inhibits KNOX in leaves
- RS2 ortholog
35
asl
KNOX expression in leaves
36
PHANTASTICA
- ARP gene
- turns KNOX off in primordium
37
ARP genes
Encode Myb TFs
38
Timing of leaf evolution
- c425Mya; earliest land plants
- c360-409Mya; leaves formed in Devonian
- c130Mya; flowers formed in Cretaceous
39
Cooksonia
- leafless fossil
- branched axis supporting terminal sporangia
- c400Mya
40
Leafless fossils
- Rhynia
- Asteroxylon
- Psilophyton
- study absence/arrangement of vasculature
41
Rhynia
- 410Mya
- lycophyte stem lineage
42
Asteroxylon
Lycophyte (pre-microphyls)
43
Psilophyton
- monilophyte stem lineage
- pre-euphyllophyte megaphylls
44
At the very least, there are
2x Leaf origins, 50My apart
45
Microphylls
- simple vein
- simple shaped leaf
46
Megaphylls
Tries to unify many types of leaf
47
Lycophytes
Microphylls
48
Telome theory of leaf evolution intro
- explains fossil trajectory
- leaves evolved from flattened branches
49
Telome theory of leaf evolution
1) branching
2) overtopping (Actinoxylon); dominant branch
3) planation (Archaeopteris); flattening
50
How does the telome theory of leaf evolution explain M/M divide?
Megaphyll - fusion
Microphyll - reduction
51
Enation theory of leaf evolution
1) leaves evolved through lateral outgrowth from unbranched axes
2) followed by vascularisation
52
Sterilisation theory of leaf evolution
- leaves evolved through sterilisation of lateral sporangia
- Zosterophyll
53
Selaginella kraussiana
- lycophyte (v. hard to transform£
- dichotomous prostrate branching pattern; v. rigorous
- meristems bifurcate
- major and minor branches in specific leaf pairs w/ specified rhizophores
54
S. kraussiana counting mechanism?
- SkKNOX1
- SkKNOX2
- no 1:1 ortholog
- conserved expression patterns
- in indeterminate equivalent
- where leaf is budding
55
SkKNOX
- present in meristem
- different to angiosperms!
- conservation of pattern
56
In order to prove function
you have to KO
57
35S:SkARP1
- complements asl
- transgene expression matches degree of rescue
58
Independent recruitment of KNOX pathway
- at least twice
- >30My apart from
- did it arise de novo?
59
KNOX expression in bifurcating shoot
When meristem bifurcates, KNOX does too
60
KNOX hypothesis
- SkARP expression makes KNOX genes switch off in that cleft at the time the meristem needs to branch
- facilitates bifurcation
- can’t prove until KO
61
Independent recruitment of pathway to enable leaf evolution
1) KNOX promotes cell division in apex of multicellular sporophyte (Bryophyte stem lineage)
2) acquired for branching (Lycophyte stem lineage)
3) KNOX leaves (Lycophytes)
62
How many times has it happened in euphyllophytes?
Open q!
