L21 - Developmental Plasticity and Domestication Flashcards
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?
- 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
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?
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
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?
- 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
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?
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
Describe the difference in tb1 between maize and teosinte and the relevant evidence
- Very similar genes
- Difference in promoter region (evidenced by increased number of polymorphisms in this region)
- All modern maize has very similar promoter sequence
What are the orthologous genes to TB1 in Arabidopsis?
How can transcription levels of these genes be modulation by environmental factors?
- 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
Briefly describe the significance of the development of dwarf varieties of wheat
- 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
Describe the genetic basis for Dwarfing and the relevant evidence
- 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
What is significant about both of the examples so far in terms of their growth repression?
- Constitutive growth repression
- Crops lose ability to respond to neighbours (reduced plasticity)
- Extreme phenotypes
Give an example of a crop that has had its yield increased by increasing branching
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
Was the green revolution world wide?
Describe a crop that hasn’t benefitted from improvement yet
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
