Genetic Specification of floral organ identity. Initiating floral development. Deciding when to initiate flowering - induced mutations -in Nature

Transcription

1 Genetic Specification of floral organ identity Initiating floral development Deciding when to initiate flowering - induced mutations -in Nature

2 Flower structure of rabidopsis Stamens arpels Petals Sepals In rabidopsis: Whorl 1 Whorl 2 Whorl 3 Whorl 4 4 sepals 4 petals 6 stamens 2 carpels

3 Why rabidopsis? - short generation time, 8 weeks from seed to seed - small, easily grown at high density in glasshouse or culture room - diploid, small genome size, 125 Mb - genome completely sequenced, 25,000 genes - efficient transformation by grobacterium-mediated transformation - many mutants described

4 Mutations that affect flower development placed in classes lter the organs formed in two adjacent whorls mutants : affect sepals and petals mutants : affect petals and stamens ntirrhinum mutants : affect stamens and carpels arpels Stamens Petals Sepals

5 Specification of floral organ identity occurs in four circular domains called whorls and is controlled by three genetic functions called, and

6 apetala2 function mutations affect flower development in Whorl 1 and 2 apetala2 Wild-type Sepals petals stamens carpels carpelloid organs bsent or stamenoid normal normal

7 function mutations affect flower development in apetala3 Whorl 2 and 3 pistillata Sepals petals stamens carpels normal Sepals or absent carpelloid normal Wild-type

8 function mutations affect flower development in Whorls 3 and 4 agamous Sepals petals stamens carpels normal normal petals Sepals and flower inside a flower Wild-type

9 nalysis of mutant phenotypes suggested model sep pet stam carp function - PETL1, PETL2 function - PETL3 PISTILLT function - GMOUS Overlapping functions provide new identities opposes and opposes

10 Interpretation of mutant phenotypes according to model Wild type sep pet stam carp mutant carp stam stam carp mutant sep sep carp carp mutant sep pet pet sep

11 Double mutants Leaves in 1st and 4th whorl Modified petals/stamens in second and third More whorls pi ag double mutant / loss of and function ll whorls are sepals Wild-type More whorls ap2 pi double mutant / loss of and function ll whorls are carpels ap2 ag double mutant / loss of and

12 Interpretation of double mutant phenotypes according to model Wild type sep pet stam carp mutant sep sep sep sep mutant carp carp carp carp mutant L S/P S/P L

13 triple mutant phenotpe ap2 pi ag triple mutant / loss of function ll whorls leaf like mutant leaf leaf leaf leaf

14 MDS box transcription factors play important roles in floral development P1, P3, PI, G are MDS box transcription factors M : MM1 yeast : gamous D : Deficiens, ntirrhinum function gene S : serum response factor, humans P2 - another class of transcription factor

15 MDS box TFs have been amplified in the plant lineage and P2-like are plant specific Genome sequencing programmes allow the number of transcription factors belonging to each family in different organisms to be counted MDS P2-like rabidopsis Drosophila 2 0. Elegans 2 0 Yeast 4 0

16 Structure of plant MDS box transcription factors MDS I K MDS transcription factor MDS - DN binding I - intervening region K - protein-protein interactions - carboxy-terminal domain ind DN through a conserved DN sequence called rg ox (/T)6GG

17 Patterns of expression indicate that spatial control is regulated mainly at the level of transcription gamous function Expressed in whorls 3 and 4 petala3 function Expressed in whorls 2 and 3

18 Misexpression from the 35S viral promoter in transgenic plants supports proposed roles of function genes Wild type 35S::P3 35S::PI Wild type sep pet stam carp 35S::P3 35S::PI pet pet stam stam

19 The function gene P2 is an exception: expressed in all whorls but only active in 1 and 2 whorl Wild type sep pet stam carp

20 Regulation of Floral organ identity gene expression P1 ( function) misexpression in ag ( function) mutant Wild type ag mutant sep pet stam carp sep pet pet sep P1 mrn in Wild-type plants Only in whorl 1 and 2 P1 mrn in ag mutant plants In all whorls

21 Further additions to the model : SUPERMN Wild type sep pet stam carp superman sep pet stam stam

22 SUPERMN is expressed at the boundary between the third and fourth whorl Stage 3 Stage 4 SUP encodes a likely zinc-finger DN-binding protein containing ys2 His2 type zinc fingers and a Serine/proline rich activation domain.

23 Wild type model Summary SUP sep pet stam carp : Stamens : arpels : Petals : Sepals

24 Web site - this presentation -PDFs WE DDRESS: Forschung bt. Entwicklungsbiologie de Pflanzen George oupland