Patterning the Arabidopsis fruit

Arabidopsis fruit structure

replum

valvemargin

valve

valve

valvemargin seed

Arabidopsis fruit opening

replum

Fruit dehiscence promotes seed dispersal

valvevalve

Genes involved in seed dispersal in Arabidopsis can control loss of yield in oilseed crops

Genes involved in seed dispersal in Arabidopsis can control loss of yield in oilseed crops

StigmaStyle

OvaryValveReplum

SeedDehiscenceZone (DZ)

DehiscenceZone (DZ)

Replum

Valve

Note that DZ = Valve Margin

Genes Controlling Fruit Development

replum

valvemarginvalve

?

?

?

wild type shp

SHATTERPROOF (SHP) gene is required for valve margin formation

Genes Controlling Fruit Development

replum

valvemarginvalve

?

?

SHP

wild type ind shp

IND and SHP are required for valve margin formation

IND is expressed in stripes at the valve margin and is positively regulated by SHP

wild type shp

replum valvevalve margin

Genes Controlling Fruit Development

replum

valvemarginvalve

?

?SHP

IND

How is SHP and IND expressionlimited to the valve margin?

replum

valvemarginvalve

SHPIND

??

FRUITFULL (FUL) transcription factor is required for valve cells

ful

Valve cells

FUL is expressedin valve cells

fulwild type

wildtype

SHP and IND are ectopically expressed in ful mutant valves

fulmutant

Wild type

IND expression

valve

valve

SHP and IND are negatively regulatedby FUL in the valves

fulmutant

Wild type

IND expression

Is the fruitfull mutant phenotype caused by ectopic expression of the valve margin (SHP, IND) genes?

The failure of ful-mutant fruit to elongate is restored by mutations in shp and ind

Wild type

shp ind ful

ind1 ful

shp ful

ful

The fruitfull mutant phenotype is caused bymis-expression of SHP and IND

Wild type

shp ind ful

ind ful

shp ful

ful

“Valve” is the “default” state

FUL is expressed in valve cells where it functionsto negatively regulate SHP and IND

replum

valvemarginvalve

enb

SHPIND ?FUL

replumless (rpl) mutant fails to form a replum

replumreplum

rplWild type

RPL encodes a homeobox protein and

is expressed in the replum

RPL

Are SHP and IND ectopically expressed in the rpl mutant

replum?

IND is ectopically expressedin the rpl mutant replum

IND expression

rpl mutant

wild type

VM VM

R

Is the replumless mutant phenotypecaused by the ectopic expression

of the valve margin genes?

Mutations in SHP rescue rpl

Wild type rpl rpl shp

RPL is expressed in the replum and functions to negatively regulated SHP and IND

replum

valvemarginvalve

SHPIND

RPLFUL

What happens in the ful rpl double mutant?

replum

valvemarginvalve

SHPIND RPLFUL

All valve margin: rpl ful

rpl ful

SHP and IND are expressed In the valve, valve margin

and replum regions inrpl ful mutants

valve replum valve

Genes controlling fruit development?

replum

valvemarginvalve

SHPIND RPLFUL

What happens if the FUL gene ismis-expressed in all cells of the fruit?

wild type

replum

valve

The FUL gene is normally expressed in valves

mis-expression of FRUITFULL converts replum and valve margin cells into valve cells

wild type 35S::FUL

replum

valve

D ->V Signal

V -> D Signal

ap Expressing Cells

ap Non-expressing Cells

D

V

Activation ofNotch AlongFuture Margin

Ap -> Notch -> Wing Margin = D/V Organizer

D/V Signaling Is Required for Wing Margin Formation and Wing OutgrowthD/V Organizer -> Margin Formationand Wing Growth

ap - cells

Wing imaginal disc in larva Adult wing (viewed end on) Adult wing with ap- patch

Loss of ap in Dorsal Cells -> Margin Formation

Fig. 4.4

•Interactions between cells on the dorsal and ventral surfaces of leaves result in the formation of a leaf margin, which is required for leaf outgrowth.

Phantastica mutants, like apterous mutants in flies, cannot form the dorsal surface of leaves.

•Loss of phantastica function leads to loss of leaf outgrowth.

•Partial loss of phantastica function leads to narrow leavesthat are cupped upwards due to fewer dorsal cells.

•Phantastica mutants illustrate that leaf outgrowth requiresinteractions between dorsal and ventral cells.

•Weak phantastica mutants can have “islands” of ventral cells on the dorsal surface.

•Marginal structures form at the border betweendorsal and ventral cells.

•In flies and plants, juxtaposition of dorsal and ventral surfaces induces formation of an organizing margin.

•The organizing margin controls outgrowth of the appendage.

Conclusions