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B3.0 > Leaf Development And Evolution I: What Is A Leaf > Flashcards

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

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2
Q

Monocot grass leaf

A
  • blade, ligule, sheath
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3
Q

Eudicot simple leaf

A

Blade, petiole

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4
Q

Seed leaves

A

Cotyledons

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5
Q

Reduced leaves

A
  • cactus spines
  • butcher’s broom cladode
  • whisk fern
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6
Q

What is an angiosperm leaf?

A
  • determinate lateral organ associated with a bud
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7
Q

SAMs

A
  • make leaves
  • transition from indeterminate to determinate growth via leaf primordia
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8
Q

SAM zones

A

1) central
2) peripheral
3) rib

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9
Q

SAM Layers

A

1) L1 (outer)
2) L2 (sub-surface)
3) L3 (inner)

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10
Q

SAM function

A
  • perpetuate stem cell pop
  • produce organ dedicates
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11
Q

Perturbed SAM mutants

A
  1. wuschel
  2. clavata1, 2, 3
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12
Q

Wuschel

A

Homeodomain protein Responsible for proliferating cells

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13
Q

wuschel

A
  • defective (reduced) meristem forms defective organs
  • can form axillary meristems
  • decreased CLV; less cells in central zone
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14
Q

clavata1, 2, 3

A
  • enlarged meristem
  • more cells in central zone
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15
Q

CLAVATA1, 2, 3

A

Component of receptor-ligand pathway that makes less cells in central zone

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16
Q

WUS/CLV interactions

A
  1. WUS promotes CLV expression
  2. CLV inhibits WUS zone
    - feedback inhibition
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17
Q

CLV OX

A

~ wus (due to strong inhibition)

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18
Q

Expression doesn’t always mean function

A

Just because the transcript is there, doesn’t mean the protein is

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19
Q

Stem cell maintenance

A
  • kept beneath stem cell zone
  • easy to self-regulate upon environmental cue
  • WUS = essential for stem cell identity
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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
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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
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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
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23
Q

Lineage analysis

A
  • pattern of division at each plastochrons
  • division continues at leaf base
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24
Q

Leaf initiation in tobacco

A
  • 120-180 founder cells (15x2-3x4 in a dome)
  • L1, 2 and 3 maintained
  • requires co-ordination
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25
Q

L1

A

Upper and lower epidermis

26
Q

L2

A

Palisade upper mesophyll

27
Q

L3

A

Inner mesophyll
Vascular tissue

28
Q

KNOX genes

A
  • knotted1-like homeobox
  • Homeodomain proteins bind DNA
  • green algae and land plants
29
Q

Ectopic cell division in KNOX GOF

A
  • 35S constitutive for expression
  • necessary and sufficient
30
Q

Simple angiosperms

A

Maize, antirrhinum, arabidopsis, pea, tobacco

31
Q

Simple leaf formation in angiosperms

A
  • KNOX turns off in primordium
  • what turns it off?
  • need recessive LOF
32
Q

rs2

A
  • -ve Kn1 regulator (transverse visualisation)
  • rough sheath 2
  • similar to kn1-0
  • ectopic Kn1 accumulation in leaf primordium
33
Q

RS2 and Kn1

A

Expressed in mutually exclusive domains / zones

34
Q

ASl

A
  • inhibits KNOX in leaves
  • RS2 ortholog
35
Q

asl

A

KNOX expression in leaves

36
Q

PHANTASTICA

A
  • ARP gene
  • turns KNOX off in primordium
37
Q

ARP genes

A

Encode Myb TFs

38
Q

Timing of leaf evolution

A
  • c425Mya; earliest land plants
  • c360-409Mya; leaves formed in Devonian
  • c130Mya; flowers formed in Cretaceous
39
Q

Cooksonia

A
  • leafless fossil
  • branched axis supporting terminal sporangia
  • c400Mya
40
Q

Leafless fossils

A
  • Rhynia
  • Asteroxylon
  • Psilophyton
  • study absence/arrangement of vasculature
41
Q

Rhynia

A
  • 410Mya
  • lycophyte stem lineage
42
Q

Asteroxylon

A

Lycophyte (pre-microphyls)

43
Q

Psilophyton

A
  • monilophyte stem lineage
  • pre-euphyllophyte megaphylls
44
Q

At the very least, there are

A

2x Leaf origins, 50My apart

45
Q

Microphylls

A
  • simple vein
  • simple shaped leaf
46
Q

Megaphylls

A

Tries to unify many types of leaf

47
Q

Lycophytes

A

Microphylls

48
Q

Telome theory of leaf evolution intro

A
  • explains fossil trajectory
  • leaves evolved from flattened branches
49
Q

Telome theory of leaf evolution

A

1) branching
2) overtopping (Actinoxylon); dominant branch
3) planation (Archaeopteris); flattening

50
Q

How does the telome theory of leaf evolution explain M/M divide?

A

Megaphyll - fusion
Microphyll - reduction

51
Q

Enation theory of leaf evolution

A

1) leaves evolved through lateral outgrowth from unbranched axes
2) followed by vascularisation

52
Q

Sterilisation theory of leaf evolution

A
  • leaves evolved through sterilisation of lateral sporangia
  • Zosterophyll
53
Q

Selaginella kraussiana

A
  • 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
Q

S. kraussiana counting mechanism?

A
  • SkKNOX1
  • SkKNOX2
  • no 1:1 ortholog
  • conserved expression patterns
  • in indeterminate equivalent
  • where leaf is budding
55
Q

SkKNOX

A
  • present in meristem
  • different to angiosperms!
  • conservation of pattern
56
Q

In order to prove function

A

you have to KO

57
Q

35S:SkARP1

A
  • complements asl
  • transgene expression matches degree of rescue
58
Q

Independent recruitment of KNOX pathway

A
  • at least twice
  • > 30My apart from
  • did it arise de novo?
59
Q

KNOX expression in bifurcating shoot

A

When meristem bifurcates, KNOX does too

60
Q

KNOX hypothesis

A
  • 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
Q

Independent recruitment of pathway to enable leaf evolution

A

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
Q

How many times has it happened in euphyllophytes?

A

Open q!

B3.0 (23 decks)

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