L21 - Developmental Plasticity and Domestication Flashcards

1
Q

Give two examples of where human selection has reduced developmental plasticity

Why is this at odds with the adaptive advantages conferred by developmental plasticity, as seen in the previous lectures?

A
  • Reduced shoot branching during domestication of teosinte
  • Development of dwarf wheat varieties during green revolution
  • Natural selection and human selection for food have very different criteria
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2
Q

What are does natural selection vs human selection attempt to maximise? In what sort of environment does each one act?

What implications did this have for domestication?

A

Natural selection:
- Maximise overall fitness (offspring etc…)
- Uncertain environments + stiff competition

Human selection:
- Maximise edible part of plant
- Protected environment and reduced competition

Implications:
- Shoot system affects yield
- Hence, changes in shoot architecture crucial to domestication

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3
Q

Briefly outline the relationship between teosinte and maize

What is one of the main phenotypic differences between them? Why is each phenotype beneficial within its environment?

A
  • Teosinte is closest wild relative of maize
  • Still cross-fertile
  • Domestication began over 8,000 years ago

Degree of shoot branching = major difference:

Maize benefits from less branching:
- Branch suppression + dense planting = concentration of yield in a few ears
- Allows simultaneous ripening
- Reduces light competition

Teosinte benefits from branching:
- Captures neighbours light
- Modulates seed production according to nutrient supply
- Allows “bet hedging” on timing of seed set

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4
Q

Which gene is responsible for most of the branching suppression seen in maize?

What does the gene encode and what effect does it have?

What does a tb1 maize mutant look like?

A

TB1
- Encodes a TCP TF
- Expressed in buds and delays progression of bud development
- tb1 expression higher in maize, stops buds growing into branches
- tb1 maize mutant looks like teosinte

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5
Q

Describe the difference in tb1 between maize and teosinte and the relevant evidence

A
  • Very similar genes
  • Difference in promoter region (evidenced by increased number of polymorphisms in this region)
  • All modern maize has very similar promoter sequence
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6
Q

What are the orthologous genes to TB1 in Arabidopsis?

How can transcription levels of these genes be modulation by environmental factors?

A
  • BRC1 and BRC2
  • Loss of function genes increase branching in Arabidopsis
  • BRC1 expressed in axillary meristem

In many species TB1/BRC1 modulated by environmental inputs e.g. light quality
- BRC1 upregulated when AT plants crowded to reduce branching

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7
Q

Briefly describe the significance of the development of dwarf varieties of wheat

A
  • Reduced height = less lodging and shading from neighbours
  • More resources spent on seed than stem
  • Major factor in green revolution
  • Wheat yields doubled between 1965 and 1970 in India and Pakistan
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8
Q

Describe the genetic basis for Dwarfing and the relevant evidence

A
  • Genetic basis identified in dominant dwarf mutant of Arabidopsis, gai mutant

Normal pathway:
- DELLA proteins function as growth repressing proteins
- DELLA domain allows giberellin (GA) -dependent interaction between DELLA proteins and GA receptor, GID1
- Complex interacts w/ SCFGID2, results in ubiquitination and degradation of DELLA
- Stem elongation promoted
- GA normally strongly influenced by environment e.g. shading by neighbours

GAI mutant:
- DELLA domain of DELLA proteins compromised (GA resistant)
- Stem elongation insensitive to GA

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9
Q

What is significant about both of the examples so far in terms of their growth repression?

A
  • Constitutive growth repression
  • Crops lose ability to respond to neighbours (reduced plasticity)
  • Extreme phenotypes
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10
Q

Give an example of a crop that has had its yield increased by increasing branching

A

Citrus fruits can benefit from increased branching:
- Thorns made from axillary meristems
- Two genes required for thorn identity, inhibiting WUS to make terminal organs
- Knock out of these genes = more branches and hence fruit made instead of thorns

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11
Q

Was the green revolution world wide?

Describe a crop that hasn’t benefitted from improvement yet

A

No, not all parts benefitted, especially where maize and wheat aren’t dominant crops

Example: Tef in Horn of Africa:
- Feeds 70% of 80 million population in Ethiopia
- Both drought and flood resistant
- Makes injera bread, nutritious
- Very tall and lodges frequently
- Small seeds

  • Dwarf variety not necessarily useful as long stems used for animal food
  • Other projects underway e.g. changing panicle architecture
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