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Plant Sciences > Development of Plant Architecture > Flashcards

Development of Plant Architecture Flashcards

1
Q

How are the basic fundamental features of plants controlled?

A

Genetics and interaction with the environment.

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2
Q

What underlies the developmental problem?

A

Differential gene regulation- how things are switched on and off at different developmental stages.

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3
Q

When does most of the development occur in plants?

A

Post embryonic.

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4
Q

What is general principle number 1?

What are the disadvantages of this?

A

Plants develop their body plans post embryonically.

Takes lots of energy to do this. Energy which could be used to fight off pathogens etc. Actively growing tissues are especially suseptible to attack because they have not yet laid down strong secondary cell walls.

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5
Q

What is general principle number 2?

What is plasticity?

A

Plants have great developmental plasticity.

Many aspects of plant development are altered in response to external conditions- These traits are considered PLASTIC.

Plasticity itself is genetically determined and specific to species, trait and environmental cue.

Plasticity is itself strongly controlled by genotype. Plastic responses are not random – they are specific for the character and for the environmental stress/cue and they have specific adaptive or maladaptive value.

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6
Q

What is canalisation?

A

Plant form is not 100% dependent on environment- Many traits are CANALISED.

Canalisation reflects developmental robustness.

Phenotype is 100% predictable for a given genotype.

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7
Q

What do seedlings emerge with?

A 
Embryonic stem (hypocotyl).
Embryonic root.

Apical/basal radial axes.

Embryonic leaves (cotyledons). 
Shoot and root tips.
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8
Q

What is general principle number 3?

A

Plants grow from meristems.

Shoot and root tips each have a MERISTEM- A central packet of dividing stem cells which fuel the growing plant body.

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9
Q

What is general principle number 4?

What is a module?

What is Iterative growth?

A

Meristems produce plant parts sequentially.

In contrast to animals and somites etc.

Module (Phytomer)
a plant “quantum”
this basic structure is canalised.

Iterative growth-
continual addition of modules.

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10
Q

What is general principle number 5?

A

Growth is often indeterminate.

Meristems do not produce a ‘set number’ of modules.
(contrast to the determined somite number in segmented animals).

Environmental control is significant here.

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11
Q

When are meristems established?

A

During embryogenesis.

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12
Q

What experimennt can be performed to determine whether cell fate is assigned by lineage or position?

A

A sector experiment to test:
Induced the expression of the GUS enzyme in one of the two apical cells in the proembryo (2-cell) stage. GUS enzyme activity can be measured by BLUE colour product. (GUS from a Cre-Lox system induced by heat shock).

What pattern expected if fate by lineage alone- one cotyledon completely blue and one completely white.

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13
Q

What is general principle number 6?

A

Cell fate is assigned by position.

Positional cues are important to direct plant development.

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14
Q

What is apical-basal polarity, and what is it critical for?

What are some mutants?

A

Apical-basal polarity (positional cue) is critical for meristem formation.

monopteros (mp), bodenlos (bd), gnom (gn).
When these genes were cloned =
All involved in AUXIN signaling. PAT is lost oin these mutants.

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15
Q

What are auxins?

A

Auxins:

  • endogenous plant hormones.
  • main plant auxin is Indole -3-acetic acid (IAA).
  • AKA Involved in Almost Anything.
  • An important positional cue.
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16
Q

What is DR5::GFP?

A

A reporter for auxin.
DR5= promoter active in presence of auxin.
GFP= green flourescent protein.

Shows polar auxin transport. Also showed that auxin itself was moving towards the basal position.

17
Q

What are PINs?

A

Membrane-localised auxin efflux transporters.

PIN triple mutants look similar to auxin signaling mutants and show a loss of PAT

PIN function and PAT is essential for embryonic axis formation

18
Q

How are PINs able to drive Polar Auxin Transport (PAT)?

A

PINs change their localisation in membrane to specific sides of the cell during embryogenesis; the PINs themselves become polar.
eg. PIN1 protein tagged with GFP moves to the basal side of central embryo cells during 16-cell stage

19
Q

What are the dynamic localisation patterns for PIN1, PIN4, and PIN7?

A

Act together to first pool auxin in the apical part of the embryo.
Then reverse the flow to the basal cells.
Then to the cotyledon tips.

20
Q

What do functional meristems do?

A

Once formed in embryogenesis, functional meristems generate primordia that form various parts of the plant such as leaves.

21
Q

What are the meristematic zones at the shoot tip?

A

Central zone- Cells in the central zone are a pool of undifferentiated stem cells.

Peripheral zone- Cells in the peripheral zone proliferate and differentiate into lateral organs.

Rib meristem- Cells in the rib meristem proliferate and differentiate into the stem.

22
Q

What are wuschel and clavata3, and what do they do?

A

WUSCHEL (WUS), a transcription factor expressed deep in the meristem organising centre (OC), promotes division in the overlying meristem.

CLAVATA3 (CLV3) – a small mobile peptide is secreted by the overlying cells, binds to the CLV1/2 receptor and negatively regulates WUS.

Antagonism between CLV3 on WUS ensures that the meristem size remains constant.

23
Q

What do KNOX1 genes do?

A

KNOX1 genes maintain the meristem in an indeterminate state.

Class I KNOX genes (KNOX1) - KNOX means Knotted-like homeobox.

Encode transcription factors.
Expressed in meristem.
Help maintain indeterminate growth.
Not expressed in incipient primordia.

24
Q

Where are meristem markers excluded from?

A

Lateral primordia.

KNOTTED (a KNOX1 gene) mRNA accumulates in the meristem but excluded from leaf primordia of Zea mays (maize). Down-regulation of KNOX-1 genes (that promote indeterminacy) contributes to the determinate growth pattern of most leaves.

25
Q

What is STM and why is it important?

A

STM., a KNOX1 gene, is necessary for SAM formation in Arabidopsis

26
Q

What can KNOX genes do? What is a mutant of this?

A

KNOX1 genes act in part by stimulating cytokinin (a plant hormone) synthesis.

The shootmeristemless1 mutant (stm1) fails to initiate a shoot apical meristem. This mutant can be rescued by cytokinin (CK) application or by expression of the cytokinin-biosynthesis IPT gene at the SAM by the STM promoter.

27
Q

What does overexpression of KNOX1 do?

A

Overexpression of KNOX1 (KNOX-OE) genes increases indeterminacy and complexity.

Plant Sciences (16 decks)

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