Leaf Development & Evolution- 4 lectures

Question 1

indeterminate meristem function

Answer 1

leaf primordium and SAM in the middle

made up of ‘zones’ and ‘layers’, made up of different cell types

Question 2

function of the SAM

Answer 2

to produce a stem cell population, and produce derivatives which give rise to organs

Question 3

reduced meristem phenotype

Answer 3

wuschel

Question 4

enlarged meristem phenotype

Answer 4

clavata 1,2,3- more cells in the central zone

Question 5

WUS and CLV interactions

Answer 5

wus ptomotes clv expression

clv inhibits wus - feedback loop which maintains an appropriately sized SAM

Question 6

chimera

Answer 6

mutation in a plant which leads to 2 different cell types- can use these to look at how different cell types organise themselves

Question 7

how can you do lineage analysis by manipulating the SAM?

Answer 7

irradiate different bits, and look at what doesn’t develop- e.g. as a proportion of the leaf, can go back to how many cells are likely to have been present at that point

Question 8

KNOX genes

Answer 8

knotted1-like homeobox genes, involved in the switch from indeterminate to determinate development

Question 9

KNOX mutants:

Answer 9

-have no SAM (loss)
-have extra cell divisions (gain)

Question 10

KNOX expression

Answer 10

on in the meristem, off in the primordium

Question 11

what turns KNOX genes off where it isn’t needed?

Answer 11

rs2- shows a similar mutant phenotype to KNOX gain of function, and possibly mutually exclusive domains- suggests inhibition

ARP genes also

Question 12

when did leaves develop first?

Answer 12

around the devonian

Question 13

KNOX evolutionary consevation

Answer 13

seems to be similar expression in KNOX in lycophyte and eudicot models- but no direct orthology

Question 14

experiment which looked at KNOX evolutionary conservation

Answer 14

cross-species complementation experiment between a lycophyte and a eudicot- seems like it can rescue, so probably does have the same function

Question 15

4 phyllotactic patterns

Answer 15

alternate- 180
opposite- pairs at 90
whorled- multiple leaves at the same point on the stem
spiral- 137.5

Question 16

phytomer

Answer 16

repeated unit along the stem

Question 17

how does patterning work at the meristem?

Answer 17

the stem cells are at specific points, and cause the merustem to bifurcate

Question 18

what seems to be responsible for leaf initiation?

Answer 18

PIN1- create directional flow of auxin, which then promotes growth- both required

Question 19

PIN1 polarity

Answer 19

regulated by microtubule orientation, and creates auxin maxima

Question 20

leaf axes

Answer 20

proximo-distal (up/down)
medio-lateral (across)
adaxial-abaxial (top and bottom)

Question 21

features of the ab/adaxial axis

Answer 21

patterns of stomata, arrangement of xylem and phloem, position of organs (one side will be closer to the meristem)

Question 22

adaxialisation/abaxialisation protein

Answer 22

Phb- adaxialise
Kan- abaxialise (K and B come before P and D)

Question 23

regulation of ad/ab axis

Answer 23

RNAi- miRNA expressed on the abaxial side to take out Phb

Question 24

when and how is the SAM established?

Answer 24

heart stage- STM and CUC expression, STM defines SAM and CUC establishes the boundaries of it in a feedback loop where STM restricts CUC

Question 25

medio-lateral specification- important genes

Answer 25

WOX and NOX
>WOX suppressed NOX, in monocots

WOX expands the leaf blade by promoting auxin biosynthesis

Question 26

words for equal/unequal growth

Answer 26

isotropic- equal growth in all directions
anisotropic- expansion in a different orientation

Question 27

what induces ectopic lobing?

Answer 27

KNOX turning off GA, creating lobing
gives you auxin maxima at the tips of the outgrowths

Question 28

gene expressed in lobe sinuses

Answer 28

CUC2- forms a growth-restricted boundary

Question 29

KNOX and compound leaves

Answer 29

overexpression seems to lead to overcompounding

Question 30

hormone responsible for compounding alongside KNOX

Answer 30

cytokinin- overexpression creates compound leaves

Question 31

3 functions of auxin maxima

Answer 31

precedes leaf initiation, leaflet initiation, lobe initiation

Question 32

KNOX in simple vs compound leaves

Answer 32

gets turned off in simple leaves after primordium initiation, but turns back on in compound leaves

Question 33

how can KNOX be repressed at the leaf margins?

Answer 33

LMI1 TF- repressed KNOX at leaf margins
RCO- a LMI1 duplicate which is only present in compound leaves- mutants seem to have less compound-ness, but not none

> changes in which proteins are required in different plants

Question 34

LFY

Answer 34

alternaitve to KNOX for compound leaf development- also used in flower development, both seem to be able to be used for leaves though

Question 35

trichome

Answer 35

outgrowths on plants/algae- hairs, scales etc, vary in structure and function

Question 36

model of trichome expression

Answer 36

GL1, GL3, TTG transcription complex activates GL2 which initiates expression. also activates TRY, which represses GL2 expression in nearby cells, creating a spaced pattern

Question 37

how is spacing maintained?

Answer 37

lateral inhibition- activator and inhibitor both being activated so you get spacing automatically

Question 38

trichosome development in roots vs shoots

Answer 38

in shoots- lateral inhibition- in roots, not as random, only cells next to cortex cells are activated

Question 39

alternative to GL1

Answer 39

WER- derived from an older pathway

Question 40

what determines vein structure?

Answer 40

the adaxial-abaxial patterning in the primordium

Question 41

canalisation

Answer 41

causing a flow of auxin into the leaf primordium, increasing flow further down