Fertilisation and Embryogenesis

Question 1

Flowering

Answer 1

Number of flowers correlated w yield

Question 2

Gamete development

Answer 2

Male and female gametes
Importance of quality and quantity

Single diploid undergoes meiosis to 4 cells w single copy of genome

Question 3

Gametogenesis - female

Answer 3

3 rounds of mitosis - splits nucleus into 2
Forms 1 cell w 8 nuclei
Embryo sack puts in cell walls between nuclei

Egg cell goes onto form embryo and pass on genetic material - all nuclei genetically identical
Synergid cells pump out signals to attract pollen tube to ovule
Breaking of cell to allow tube to grow into embryo
Central cell is fertilised and makes endosperm
Encounters other cell of female gametophyte - nuclei fuse to form diploid
Fertilised by sperm cell nuclei - form triploid endosperm

Question 4

Gametogenesis - male

Answer 4

4 microspores need to turn into pollen grains
2 rounds of mitosis:
Round 1 - splits nucleus so 1 contained in cell wall of other
Round 2 - nucleus divides forming 2 sperm cell nuclei (1 to fertilise central cell and other for egg cell)
Pollen grain is triploid by the time it germinates

Question 5

Pollen germination

Answer 5

From anther to stigma
Needs liquid from stigma to hydrate when germinating
Pollen tube germination from stigma to ovules - specific direction

Question 6

Fertilisation

Answer 6

Pollen tube has to release sperm cell nuclei in ovule
Fuse w correct nuclei from enbro sack for fertilisation

Pollen grain lands on stigma and pollen tube grows down style to find ovule
Double fertilisation of central and egg cell after bursting
Tube attracted to unfertilised ovules and needs to find micropyle opening where synergid and egg are

Question 7

Embryogenesis

Answer 7

Producing new seedling

Dicots: embryonic stages (octant -> globular -> heart -> torpedo)
Monocots: primitive embryo at bottom of grain; most of seed is endosperm w starch for energy when germinating

Question 8

Seed filling

Answer 8

Put energy into grain so seed has energy to grow and establish

Question 9

Increasing yields

Answer 9

Change architecture:
Seed size - more nutrition
Flower architecture - more seeds onto spikelets and more spikelets on plants
Plant architecture - shorter and more grains

Question 10

Changes to cultivated rice

Answer 10

Alter changes from past further

Near isogenic lines: cultivated and WT
Mix DNA of genes from female and male parents to mix chromosomes
Backcross to 1 parent to dilute out genes from other parent
Homozygous

Question 11

Near isogenic lines

Answer 11

GL6 gene from cultivated rice put in WT
Got bigger grains but reduced seed yield per plant - larger but fewer seeds
Selected for larger grains

Question 12

Genetic abortion of floret development

Answer 12

Sterile flowers in some grain species

e.g. rice - 2 sterile lemma, ancestor likely had 3
2 flowers became sterile due to G1 gene

Question 13

Climate change

Answer 13

Reproducyion very sensitive
Cold can cause abortion of pollen grains in rice
Drought causes fewer ears in wheat
Heat causes fewer pollen grains, germination and reduces viability in tomatoes - less starch so little energy
Heat causes smaller embryo sacks and signalling issues for pollen tubes in wheat

Question 14

Impacts of climate on fertilisation

Answer 14

Pollen has to travel to find ovule - follows signals as guide
Removal of important protein resulted in fewer seeds as pollen tubes were overgrown and didn’t burst - proteins important to regulate this

Proteins on female side expressed in synergid and some in egg; work w other proteins
Proteins on pollen tube important for communication

Question 15

Genetics for breeding

Answer 15

Use old landraces and related species to find important variants

Question 16

Crossing germplasm

Answer 16

Start w heterozygous (not good - gives different progenies) - homozygous more stable as 2 copies of same gene (no further change in genetics)
Heterozygous genome - some genes from WT have advantageous and disadvantageous traits

Question 17

Near isogenic lines

Answer 17

Progeny will be heterozygous

1 copy of each parent chromosome
Backcross many times to get DNA from preferred background w small sections from other parent

Question 18

Recombinant inbred lines

Answer 18

Take heterozygous plant and self it
Mostly homozygous after many generations
Equal genetic contributions from each parent

Question 19

Speed breeding

Answer 19

Only if yield is not an issue
Fast life cycle:
Outside = 1-2 gen per year
Glasshouse = 2-3 gen per year
Increased light and day = 6 gen per year

Early flowering and fewer seeds
Increase plant density so they flower faster

Question 20

Double haploids

Answer 20

Hetero to homozygous plants
Dissect out microspores which form pollen grains
Reprogramme to enter cell division - haploid cells divide through mitosis
Some form embryo like structures (use of tissue culture)
Think they’ve been fertilised
Induce genome doubling
Makes diploid
Homozygous throughout entire genome

Question 21

Maize pollen to pollinate wheat

Answer 21

Fertilisation of wheat embryo sack by maize sperm cells
Chromosome can’t separate properly so maize lost - only wheat chromosome maintained
Ends up as haploid
Oxen treatment - fertilised embryo sack continues cell division
Maintain early embryo development
Dissect out immature embryo before it’s aborted
Get homozygous plant in 1 gen

Question 22

Haploid inducer plants

Answer 22

Centromeres marked by proteins - important for chromosome segregation during mitosis and meiosis
Transfer constructs into heterozygous plants - select mutants w constructs

Null mutant version:
Goes through mitosis but no meiosis
Male is sterile so no pollen, reduced female fertility