L18 - Introduction to Plant Development and Meristems Flashcards

1
Q

What are the advantages of studying a small number of model plants?

A
  • Traits like short lifecycle and lots of progeny
  • Often beneficial to have many researchers working on one organism (builds a more complete picture and often conserved)
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2
Q

Give the main differences between plant and animal development and why this emerges

A

Plants are generally indeterminate
- Autotrophs, must create large SA

Very plastic development

Plants have no unique parts
- Subject to herbivory so must survive if one part eaten

Cell wall inhibits cells rearranging so development controlled by division + elongation

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3
Q

Where are meristems present and what is their function?

Describe the shoot apical meristem in more detail

A

Present at growing tips of plants
- Shoot apical meristem, root apical meristem, auxillary meristems

Shoot Apical Meristem:
- Dome of cells w/ central zone of slowly dividing stem cells
- One daughter cells remains stem cell in meristem
- Other daughter cell fed into meristem periphery for rapid division and stem/leaf formation

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4
Q

Describe the function of the shoot apical meristem maintenance feedback loop and its general mechanism in 5 steps

A

Maintains meristem identity

1) WUSCHEL TF expressed in middle of SAM.

2) WUS promotes CLV3 peptide

3) CLV3 peptide binds CLV1/2

4) CLV1/2 inhibit WUS, reducing meristem growth

5) Less meristem = less WUS = reverse occurs

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5
Q

How does WUS move and what is the evidence for this?

What is the effect of stopping this movement?

How does CLV3 move?

A
  • WUS moves via plasmodesmata between cells
  • Evidence as WUS RNA detected in smaller central meristem region than WUS protein
  • Blocking movement by inducing extra callose production in WUS domains arrested meristem
  • CLV3 seen in extracellular space in cell walls
  • Moves apoplastically
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6
Q

Aside from the WUS and CLAVATA genes name another gene that is used to maintain the meristem

A

SHOOT MERISTEMLESS (STM)
- Mobile TF, prevents cells obtaining organ identity
- Broader expression than WUS
- Works with WUS to induce CLV3
- STM mutants don’t maintain meristems, all converted to lateral organs

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7
Q

Why is auxin thought to be important in phyllotaxis?

Describe how auxin is transported through plant tissues

A

Inhibition of organ formation by an organ thought to be through auxin depletion

  • Auxin transported through plant tissues by specific influx + efflux proteins
  • Can also passively diffuse into cells but not out of cells
  • Most commonly imported by PIN transporters + exported by PIN-FORMED transporters
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8
Q

Explain Hofmeister’s general model for phyllotaxis

Draw the relevant diagram

A
  • New organs form on active ring in peripheral zone of meristem (central zone excluded)
  • New organ inhibits other organs forming near
  • Meristem grows, moving organ away
  • Zone of inhibition reduced until low enough for new organ formation to initiate

(See diagram on pg 7)

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8
Q

What is phyllotaxis?

Describe the four most common patterns observed

A

Phyllotaxis - Arrangement of repeat plant organs around the stem e.g. leaves

Spiral: Organs at 137.5˚

Decussate: Two opposite leaves then 90˚ shift with two more opposite leaves

Distichuos: Leaves produced one at a time at 180˚ to each other (common in grasses)

Whorled: Many leaves made at once

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9
Q

Give two examples of plant phenotypes that show the importance of auxin in organ formation

A
  • PIN mutants has no flowers, only a naked inflorescence (pin like)
  • 1-N-Naphthylphthalamic acid (NPA) inhibits PIN transporters, gives “pin” phenotype
  • Auxin application to NPA treated or PIN meristems restores organ function (transport of auxin via PIN auxin dependent)
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10
Q

Describe the mechanism in which auxin depletion influences phyllotaxis

A
  • PIN proteins polarise toward high auxin, reinforcing auxin maxima
  • Eventually, sufficient auxin causes outgrowth
  • Auxin maxima causes STM reduction, allowing organ formation
  • Surrounding area depleted of auxin, inhibiting new organ formation
  • Relative size of meristem compared to primordia gives different patterns
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11
Q

Describe how the different parts of a flower develop and how the flower is made determinate

A
  • Leaves modified by A, B, C function TFs to produce different floral organs
  • AG gene shuts off WUS in floral meristem after carpel development
  • Floral meristem used up, making flower determinate
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