Gemetogenesis and pollination

Question 1

Gametogenesis involves a number of basic cell-biological processes. Which?

Answer 1

• mitosis
• cell wall formation
• nuclear migration
• nuclear fusion
• cell death

Question 2

What is one of the big differences between animal and plant development?

Answer 2

In Animals the germline is set aside early in develoment.

In plants the new germlines arises from the meristem.

Question 3

How do plants initiate the transition from somatic to germline fate?

Answer 3

the germnaton switch- deteminig MMC formation
* without KIP-Related Proteins (KRP) or Retinoblastoma Related proteins (RRP) several cells enter meiosis, insted of just one. -> Multile gametophytes are formed
* Cell fate acquisition depends heavily on cell-to-cell signalling, but there is still a lot we don’t know

Question 4

Sporophytic mutations

Answer 4

• Mutant sporophyt and WT female gametophyt
• affect genes that are required in the diploid tissues of the mother (or father) plant
• heterozygous mutant plants show a wild-type phenotype
• homozygous mutant plants are fully sterile
• show Mendelian segregation (1:2:1)

Question 5

Gametophytic mutations

Answer 5

• WT sporophyte and Mutant gametophyte
• affect genes that are required in the haploid gametophyte itself
• heterozygous mutant plants are semi- sterile
• homozygous mutant plants are never found
• do not show Mendelian segregation ratio (1:1)

Question 6

Screening strategies for gametophytic mutations

Answer 6

• direct visual screen
• segregation distortion of resistance markers (T-DNA with Resistance gene -> allows selecting plants hat carry transgene)
• gene expression (gen-trapping / enhancer-trap; transcriptomics)

Question 7

The life cycle of flowering plants: Pollination and pollen tube growth

Answer 7

Pollen lands on the stigma, hydrates and the pollen tubes grow towards the ovule with high efficiency and precision.

1) Landing (Self incompatibility?)
2) Entry into female tissue
3) Growth through transmitting tract
4) Exit from transmitting tract and growth to the next ovule
5) Growth to the micropyle -> needs a targeting signal from the female gametophyte

The synergid cells produce a chemotactic signal for pollen tube guidance. (After fertilization the signal is no longer produced.)

• small cystein rich peptides (CRPs) attract pollen tubes -> LURE peptides
• Peptides are recognized by a receptor- like kinase (PRK6) at the tip of the polen tube (Transmembrane receptor)
• genes are expressed in the synergids and peptides are secreted onto the micropyle region

Interaction between male and female gametophyte.

Question 8

What causes pollen tube burst?

Answer 8

• Pollen tubes burst in response to female CRPs in a species-specific manner
• Signalling from the female causes depolarization of pollen tube membrane, influx of K+ and osmotic tube burst

Question 9

Pollentube burst- WHAT HAPPENS ON THE MALE SIDE?

Answer 9

• Two receptor kinases are responsible for pollen tube burst
• anx1 and anx2 receptors are localized polarly to the pollen-tube membrane
• control when the pollen tuve should burst

Question 10

When do the two fertilisation events happen? And are the sperm cells equivalent?

Answer 10

• the two fertilization events are near simultaneuous
• the two sperm cells are equivalent. Either sperm cell can fertilize the central cell or the egg cell
• Eine fusioniert mit der Eizelle → Bildung der diploiden Zygote.
• Eine fusioniert mit den Polkernen → Bildung des triploiden Endosperms.

Schlüsselmoleküle:
GCS1/HAP2: Erforderlich für die Fusion männlicher und weiblicher Gameten.
EC1-Peptide: Unterstützen die Befruchtung, indem sie die Spermazellen aktivieren.

Question 11

What happens after fertilization?

Answer 11

• Pollen tube enters through the micropyle and discharges its two sperm cells into one of the synergids
• Double fertilization is unique to flowering plants and Gnetales (a type of gymnosperm)
• Remember: Successful fertilization requires extensive signalling between the gametophytes and the gametes