Fertilisation and Embryogenesis Flashcards
(20 cards)
What are the main steps of fertilisation underlying crop yield?
- Flowering
- Gamete development
- Pollen germination
- Fertilisation
- Embryogenesis
- Seed filling
What happens during gametogenesis in male plants?
Production of male gametes occurs in anthers
- Diploid microspore mother cell undergoes meiosis into 4 haploid microspores
- Haploid microspore undergoes 2 mitotic divisions into tube cell and generative cell
- Tube cell: forms pollen tube
- Generative cell: undergoes mitosis to form 2 sperm cells in the pollen grain
What happens during female gametogenesis?
- Diploid Megaspore mother cell undergoes meiosis -> 4 haploid megaspores
- Only one megaspore survives
- Undergoes three rounds of mitosis / asymmetrical division -> embryo sac
- One cell differentiates into egg cell
- An adjacent cell has 2 polar nuclei that fuses with sperm nucleus during double fertilisation
What is distinctive about monocots in terms of embryogenesis?
Monocots (like rice, wheat, maize, barley, oats) have large endosperm remaining at the end of development
What were the key components of the Green Revolution (1960s - 80s)
- Changes in plant architecture (shorter)
- Use of nitrogen fertiliser
- Use of herbicides and pesticides
- Irrigation
- Increased yields
What architectural changes can increase crop yields?
- Changes in seed size (increasing grains per inflorescence)
- Changes in flower architecture
- Changes in plant architecture
What challenges exist in improving crop genetics?
- Complex genetics including ploidy (e.g., wheat is hexaploid)
- Most traits are quantitative with many genes of small effect
- Pleiotropic effects of genes (multiple traits affected by single gene)
- Need to understand mechanism behind each development stage
- Need to identify lines with positive yield increases
- Need to find causal changes
- Need to target key proteins/metabolites for improvement
How does climate change affect crop yields, particularly regarding pollen?
- Pollen grain number, germination, and viability are reduced at higher temperatures
- Linked to reduced starch concentration in anthers
- Lower soluble sugar concentrations in mature pollen grains
- Understanding these mechanisms is crucial for developing climate-resilient crops
What did Wang and colleagues study in rice?
What was found?
The origins of cultivated rice using Near Isogenic Lines (NILs)
Compares two rice lines: GLA4 (cultivated) and W1943 (wild)
10-20% difference in grain length between the two lines
What are Near Isogenic Lines (NILs)?
Line that are genetically identical except for a small genomic region, used to study specific trait differences
What mutation was found in W1943 rice in the Wang study?
A heterozygous premature stop codon
What is the function of the GL6 gene?
GL6 encodes a transcription factor that regulates cell number in rice grains
Increases grain size in rice by promoting more cells in the grain
Why might larger rice grains not always be beneficial?
They may lead to slightly lower overall yield per plant
What are pleiotropic effects?
A single gene or genetic variant influences multiple phenotypic traits
What are the multiple stages of reproduction that are sensitive to heat?
- Gamete development
- Pollen grain viability
- Embryogenesis and seed filling
- Cell division
- Source-sink relations
What are receptor kinases and their functions?
Signalling proteins that span the plasma membrane with:
- Extracellular domain in cell wall for signal detection
- Intracellular kinase domain for signa transmission
They function in:
- Pathogen detection
- Plant growth and reproduction
- Environmental signal detection
What are kinesins and their functions?
Kinesins are molecular motors that use ATP to ‘walk’ along microtubules.
Function in:
- Microtubule dynamics (spindle phragmoplast assembly)
- Vesicle transport to cell plate
- Nuclear migration
- Chloroplast movement
What is speed breeding?
- Used when yield is not a primary concern to achieve faster life cycles- Field conditions: 1-2 generations per year
- Glasshouse conditions: 2-3 generations per year
- With increased light level and day length: 6 generations per year
- Can be further optimized with increased plant density (~900 plants per m²)
What is the process of creating double haploids via genome elimination?
- Using GFP-tailswap plants in cenh3 null mutant
- Maternal or paternal genomes with altered histones are lost
- Changes to centromere structure impede chromosome segregation
- Results in haploid daughter cells in mitosis
- Haploid plants are mostly sterile but can produce some seeds
- Diploid progeny can be increased with colchicine treatment
What are the key conclusions about reproduction and crop yields?
- Multiple reproductive factors affect yields
- Genetic solutions can help increase crop yields
- Many reproductive steps are vulnerable to climate change
- Genetics can help mitigate climate effects on reproduction
- Breeding process can be accelerated to achieve better results
