Seed development

Question 1

Advantages of seeds

Answer 1

• Protction of teh embryo
• Dormancy
• Nutrition of embryo
• Pr- development of embryo
• Dispersal

Question 2

What causes the remaining synergid to stop producing attraction peptides (LUREs)?

Answer 2

To prevent polytubey ethylene signaling triggers synergid cell degradation, preventing further pollen tube attraction.

-> There is a polyspermy block on the plant gametes, but it can be bypassed;

Question 3

What drives endosperm development?

Answer 3

Formed after fertilization of the central cell with one sperm. -> Endosperm iniciation is driven by imprinted genes that code for auxin biosynthesis enzymes;

Functions:
* Supports embryo development
* Provides nutrients after germination

Cellularization of the endosperm is a critical developmental transition, without which the embryo dies.

Question 4

Seed coat development and what regualtes it?

Answer 4

1) Cellular growth phase
2) Cells of individual layers differentiate
3) Specialized cell types are visible
4) Cell wall thickening (formation of the columella)
-> Cellular differentiation is complete

There are no cytoplasmic connections between central cell and integuments, or endosperm and seed coat
→ The initial signal has to be able to cross membranes.

Seed coat formation requires a signal from the endosperm, which is auxin

• A mechano-sensitive layer in the seed coat detects turgor pressure from the growing endosperm.
• This pressure triggers gibberellin (GA) production, leading to cell expansion and seed coat differentiation.

Derived from maternal integuments

Question 5

Apomixis

Answer 5

Some plants can produce clonal seeds (apomixis), but the mechanisms needed to engineer this is crops are still mostly undiscovered.

Apomictic progeny leads to fixation of highly complex, heterozygous genotypes over long periods.

Three components:
1) Apomeiosis – Egg cell forms without meiosis (remains diploid)

2) Parthenogenesis – Embryo develops without fertilization

3) Autonomous endosperm development – No sperm required

Artificial apomixis approaches: MiMe (mitosis instead of meiosis) + BBM-induced parthenogenesis.