7. Polar tip growth, Planar polarity, Patterning of root hairs and leaf trichomes Flashcards
Where can polar tip growth be found?
moss rhizoids and protonemata, fern rhizoids, root hairs and pollen tube in plant evolution
What components do we find right in the tip of the root, the “clear zone”?
Endoplasmatic Reticulum, vesicles and Golgie stacks
some “apical actin structures” (actin filaments)
The familiy of small Roh-of-Plants (ROP) GTPases takes over similar roles as Rac/Roh/Cdc42 in animal cells. Names some examples!
ROP 10 and ROP 11 (ROP 6): ABA responses
(ROP6) and ROP 4: root hair development
ROP2: root hair development, cell chape formation, low oxigen response
ROP1, ROP 3 and ROP 5: Pollen tube formation
Which molecules co-localise during Hair Initiation?
Phosphatidylinositol-4-Phosphate 5-Kinase 3 (PIP5K3)
Co-localises With Sterols
A Sterol-Enriched Polar Membrane Domain Accumulates
Rho-of-plant (ROP)2 and ROP6 Proteins…
AGCVIII Kinase D6 Protein Kinase (D6PK) Undergoes
Basal-to-Planar Polarity Switching D6PK Contributes To The Regulation Of Planar Polarity of ROP Positioning
Polar D6PK Localisation Requires PIP5K3 Function and D6PK Directly Binds to PIPs
What is D6PK?
It is a late, lipid-domain dependent player with a regulatory function during planar polarity signaling, likely dependent on PIP and PIP2 binding during basal-to-polar polarity switch
When can you see a trichoblast formation latest?
on the 32 cell stage
Pattern formation in root hair cells generate 2 types of cells - which ones?
Root hair cell (is the ground state must be actively suppressed by activators of non-hair cell fate) and non-hair-cell
How does glabra2 mutants behave?
glabra2 (gl2) mutants form ectopic hairs GL2 encodes a homeodomain transcription factor preferentially expressed in non-hair cells within the meristem and root elongation
zone -> pGL2:GUS
GL2 acts downstream of WEREWOLF (WER) And TRANSPARENT TESTA GLABRA (TTG)
How does transparent testa glabra (TTG) mutants behave?
forms hair on almost every root epidermal cell
impies either role in either
I promoting specification of non-hair cell type (!!!)
or
II repressing specification of hair cell type
Encodes a WD-40 protein – WD40 domains mediate
protein interactions
How does a Werwold (WER) mutant behave?
WER encodes a MYB-transcription factor
WER can interact with GLABRA3 (GL3) and ENHANCER OF GLABRA3 (EGL3) in yeast two-hybrid assays
How does glabra3 (gl3) and enhancer of glabra3 (egl3)
double mutants behave like?
show ectopic hair formation in non-hair positions
Implies either role in either
i) promoting specification of non-hair cell type (!!!)
or
ii) repressing specification of hair cell type
Both encode bHLH proteins likely specifying non-hair cell identity
How does caprice (cpc) and cpc;triptychon (try);
enhancer-of-try/cpc1 (etc1) double and triple mutants behave like?
CPC, TRY and ETC1 – can be viewed as negative regulators of non-hair cells or positive regulators of hair fate CPC, TRY and ETC1 encode MYB-like transcriptional
regulators lacking a typical transcriptional activator domain.
Could act to repress hair formation by blocking transcription
35S::CPC produces ectopic root hairs
In the cpc mutant GL2 is not repressed which may cause
the ectopic non-hair cell formation.
Trichome mutants have identified genes involved in many processes, name some of them!
- Genes affecting spacing and identity
- Genes affecting cell cycle regulation
- Genes affecting growth and polarity
- Genes affecting cell shape
As trichomes differentiate, they endoreduplicate, causing their ploidy (DNA content) to increase from 2n to 4n to 8n to 16n. The cell cycle of endoreduplicating cells skips mitosis
Some mutants overproduce trichomes. Which ones?
cpc try; cpc try etc3
