Principles In Plant Development Flashcards

1
Q

Angiosperm development

A
  • low degree of tissue specialisation
  • high degree of tissue plasticity
  • organogenesis occurs throughout life @ meristems
  • rigid cell walls; morphogenesis occurs by differential growth, not cell movement
  • permanently rooted; and environment profoundly affects development
  • no permanent germline
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2
Q

Can predicable fate maps be determined?

A
  • Clonal analysis
  • The each spikelet pair is derived from a single cell
  • looking for patterns of shared mutation (e.g. virescence)
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3
Q

Induce sectors in mature maize embryo

A
  • irradiation creates random change
  • where is it?
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4
Q

Sector size in mature maize plant

A
  • grow the plants (1000s)
  • 18 leaves, tassel and ear
  • score where the green sectors are in the field
  • no compartments, overlap
  • no rigid fate map; plasticity
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5
Q

‘Fate map’ of embryonic maize meristem

A
  • first 5 leaves initiated @ embryogenesis
  • probability map
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6
Q

Assess growth plasticity

A

1) grow
2) remove leaves
3) place apex back in culture
4) count leaves that form
- plastic: more meristems would form
- time-shift assay

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7
Q

Are cells “used up” in the meristem?

A
  • “depleted” meristem produces entire set of leaves
  • probability, but not predictability
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8
Q

Is cellular differentiation lineage or position dependent?

A

Good q!

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9
Q

Maize leaf anatomy

A
  • C4
  • bundle sheath + mesophyll cells
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10
Q

white deficiency and ring chromsomes

A
  • a more contrived sector analysis
  • ring chromosomes contain wt gene copy (spontaneous loss during mitosis)
  • homozygous mutation on autosome: cells are white
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11
Q

Sectors of chlorophyll fluorescence

A
  • where is the white tissue in the cross-section?
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12
Q

Sector types

A
  • sectors are undermine about lineage relationships in leaf (3 layers)
  • indicates timing of mutation
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13
Q

Distinct cell types share a cell lineage

A
  • one internal cell divides to form a middle layer
  • middle layer forms all BS and mesophyll cells
  • positional
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14
Q

Indeterminate growth

A

Shoot/root

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15
Q

Determinate growth

A

Leaf, lateral root, floral organ

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16
Q

What regulates the switch from indeterminate to determinate growth?

A

Knotted1 gain of function promoter mutation in maize (Kn1)

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17
Q

Kn1

A
  • “knots” of indeterminate growth on the leaf due to ectopic expression
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18
Q

GOF

A
  • dominant genes can’t tell you what a gene is necessary for
  • you need a LOF recessive gene
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19
Q

Kn1 expression

A
  • in meristem, not leaves
  • isn’t switched off
  • causes aberrant division
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20
Q

KNOX in Arabidopsis

A
  • 35S constitutive promoter
  • KNAT1 = ortholog
  • Homeobox
  • LOF: shootmeristemless
21
Q

Sufficiency experiments

A

Express a gene ectopically

22
Q

KNAT1

A
  • ectopic expression gives extra division; lobing
23
Q

What regulates organ formation?

A

Auxin gradients

24
Q

Auxin gradients in organ primordia

A
  • auxin responsive DR5 pro motor driving fluorescent reporter gene expression
  • watch organogenesis
  • proto-leaves maxima
25
NPA on organs
- no leaves - PIN-like fluorescence
26
Discrete auxin foci allow
Organ formation
27
PIN proteins
- mutants = pin - localise to one side, outgrowth direction
28
To what extent to changes in cell division planes alter morphogenesis?
tangled maize mutants have aberrant cell divisions
29
tangled
- ‘messy’ epidermal cells - leaves feel papery
30
Quantify division plane direction in tangled mutants
- transverse divisions are completely random
31
tangled morphology
- normal shape - smaller, crinklier - supracelullar control to balance/check
32
To what extent to cells act cell-autonomously?
- Sector induction in Kn1 mutant maize plants - does Kn1 only act where it is expressed?
33
Sector induction in Kn1 mutant maize plants
- genetic mosaic analysis; removing a gene product - wt: green - homozygous recessive: white - irradiate and look for white sectors
34
Sector types in Kn1
- knots on epidermis correlate with expression of mutant allele in central leaf domain - gene is only sufficient to make knots if it is expressed in middle layer - TFs move cell-> cell via plasmodesmata
35
Kn1 TFs and plasmodesmata
- usually: 2kDa limit - these are 60 - mechanism unknown
36
Accumulation of Kn1 gene products
- Ab localisation - protein, but not mRNA accumulates in the epidermis - not expressed here
37
Confirming Kn1 protein mobility
- fuse to a fluorescent tag and object: moves out - control tag stays in
38
Root development in legumes
- changes in presence of bacteria and fungi
39
Root development in legumes process
- molecular signals initiate the interactions - plant root exudates: flavonoids, strigolactone - Rhizobia: nod factor - fungi: myc factor - root redifferentiates at site of perception into nodules
40
Nodules
- Complex vascular network - pops of bacteria
41
nod factors
- bind to cell-surface RLKs - ligand recognises binding domain
42
RLKs
- ligand binding activated internal kinase domain - downstream phosphorylation - most interacts w / environmental cues
43
Downstream of RLKs (NFR115)
- membrane depolarisation due to early ion fluxes - root tip swelling - SYMRK induces calcium fluctuations/relocalisation/spiking (RLK, MLK cascades) - TF induction for new developmental programme - root hair curling, NIN activation - infection thread formation - nodule organogenesis
44
Gametophyte
- multicellular - contains gametes
45
Ovule
- somatic tissue - megaspore mother cell specification - meiosis: haploid tetrad (3x degenerate) - remaining divide mitotically to form 8x nuclei - one doesn’t divide: 7 cells - this is the multicellular gametophyte
46
Anther
- microscopic mother cell goes thru meiosis to form tetrad - mitosis forms pollen grains - 2x sperm nuclei - 1x degenerative cell
47
Genes that restrict sporophyte no to remain discrete
- lead to more mega/microspore mother cells - small peptides - RLKs - specified cell initiates a communication cascade w/ neighbouring cells to inhibit them from becoming mother cells
48
What distinguishes germline from somatic tissues?
- neighbour differentiation - epigenetic marks on megaspore mother cell goes
49
Epigenetic marks on megaspore mother cell
- total heterochromatin volume > - H8 mother cell specification - H1 neighbouring cells