2. Basis cell division and selected specification of plants

Question 1

Who is leading the cell plate growing?

Answer 1

Actin (is attached on the cell membrane)

Question 2

How is the fenestrated sheet developing?

Answer 2

1. Phragmoplast (assembly matrix with microtubules)
2. Tubular vesicular network
3. Tubular network
4. Fenestrated sheet

Question 3

How exactly does the growing of the take place? With the help of which vSNAREs?

Answer 3

Fusion of vesicles during cell plate formation most likely occurs homotyppically mediated by the cell plate-specific KNOLLE syntaxin a v(esicle) SNAREa and its interaction partners.
The syntaxum: the type of SNARE, which is KNOLLE – one specific, firstly identifyed. They are found in different fusion events among others at the cell plate of plants and the midbody of animals. KNOLLE arrives from the trans Golgi-network

Question 4

What means “cytokinesis”?

Answer 4

Same vesicles fusion

Question 5

What happens is KNOLLE is mutated?

Answer 5

Mutants display strong vesicle fusion defects during cell plate formation –> streets of vesicles: they can often be delivered but not fuse, often one syntaxin can jump in.

Question 6

What kind of complex formation happens during vesicle fusion?

Answer 6

Cis- and trans-SNARE complex formation
There are 2 types of SNAREs working together: KNOLLE (syntaxin) and SNAP33 (or SNAP25-like)
First: 2 SNAREs pointing in the same direction (cis)
–> NSF (AAA ATPase) and alpha SNAP (2 complexes working together and connecting to build thrans SNAREs) AND VAMP (extra protein binding to KNOLLE
–> Forming a trans-SNARE complex (unknown if with or without VAMP)
–> cis SNARE complex (unknown if with or without complex)

Question 7

Severals small GTP-binding proteins are regulators of vesicular transport
What are examples for GTP binding proteins?

Answer 7

Rab-family: vesicles targeting and fusion in most pathways
Arf-family: COPI budding, Golgi vacuolar and endocytic transport
Sar1: COPII budding from ER
ARF GEFs are a big protein family, mostly arf1. They are GDP/GTP Exchange factors for ARF catalyses the transition to the active GTP-bound active form of ARF
ARF GEFs regulate vesicle transport at diverse places within the endodermal system. Name some examples!
Recycling endosomes (RE)back to cell membrane (GNOM and ARF working together and can be blocked by BFA (brefelin A)
Form Golgi network back to ER (GNL1 together with ARF)
Endocytosis for e.g. PIN proteins inside the cell, can be blocked by Auxin
Form Trans- Golgi network endosomes (TGN/EE) to PVC/MVB: prevacuolar compartement /multi vescular body