Leaf Development And Evolution 4: Patterning Cell Types

Question 1

Trichomes

Answer 1

• specialised leaf cell
• form and function differ

Question 2

Trichome differentiation

Answer 2

• affected by genes @ various stages
  1) spacing and identity
  2) cell cycle regulation
  3) growth and polarity

Question 3

Trichome generation

Answer 3

• sheet of pavement cells in epidermis
• one becomes specialised
• cellular outgrowth
• progressive endoreduplication

Question 4

As trichomes differentiate from tip -> base…

Answer 4

More endoreduplication in older cells @ tip

Question 5

A. thaliana wt

Answer 5

Relatively evenly spaced trichomes

Question 6

No trichomes

Answer 6

• gl1
• ttg1
• gl3/egl3
• gl2

Question 7

GL1

Answer 7

Myb protein

Question 8

TTG

Answer 8

WD40 protein

Question 9

GL3/EGL3

Answer 9

bHLH protein

Question 10

GL2

Answer 10

Homeodomain protein

Question 11

Clustered trichomes

Answer 11

• tryptocarn
• TRY: truncated Myb
• expressed in all cell types
• some sequence similarity to GL; can displace from TC
• non-cell-autonomous auto-inhibition

Question 12

TRY expression

Answer 12

• young leaf: ubiquitous @ base
• older leaf: trichome only

Question 13

Non-cell autonomous auto-inhibition

Answer 13

If TRY replaces GL in TC in pavement cells, it becomes inactive

Question 14

Stochastic pathway initiation theory

Answer 14

• could be activated in either two cells
• determines L/R trichome

Question 15

Stochastic pathway process

Answer 15

1) TRY and GL2: reinforced auto-expression
2) TRY moves to neighbouring pavement cells and auto-inhibits; no trichomes

Question 16

Trichomes and root hairs

Answer 16

• same pathway recruited twice
• convergent
• switch the two proteins and they are functional in each others’ contexts

Question 17

Root hairs:

Answer 17

• TTG + GL3: TA
• WER: Myb (not GL1)
• GL2 inhibits root hair outgrowth (via signal from ICS between cortical cells)

Question 18

Structure:

Answer 18

1. Trichomes (+ root hairs)
2. Stomata
3. Veins