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

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

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

6 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

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

8 nalysis of mutant phenotypes suggested model in which functions combine to create petal and stamen identities Model suggests: sep pet stam carp Overlapping functions provide new identities function must oppose and must oppose Genes conferring different functions, identified from mutants: function - PETL1, PETL2 function - PETL3 PISTILLT function - GMOUS

9 nterpretation 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

10 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

11 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

12 triple mutant phenotype ap2 pi ag triple mutant / loss of function ll whorls leaf like mutant leaf leaf leaf leaf

13 Many genes encode MDS box transcription factors Structure of plant MDS box transcription factors MDS I K Domains in MDS transcription factors 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 P1, P3, PI, G are MDS box transcription factors

14 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

15 Misexpression from the 35S viral promoter in transgenic plants supports proposed roles of function genes and demonstrates importance of spatial control of transcription Wild type 35S::P3 35S::PI Wild type sep pet stam carp 35S::P3 35S::PI pet pet stam stam

16 Wild type Regulation of Floral organ identity gene expression: opposes at the transcriptional level P1 ( function) misexpression in ag ( function) mutant sep pet stam carp ag mutant 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

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

18 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.

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

20 PETL2 is a class gene required for whorl 1 and 2, but is expressed in all whorls. How is P2 activity restricted to whorls 1 and 2? Wild type

21 rabidopsis microrn172 has homology to the P2 gene

22 microrns repress gene activity by interacting with the mrns of target genes either repressing translation or causing degradation of the mrn

23 Expression of MIR172 from a viral promoter causes an ap2 mutant phenotype WT ap2 mutant 35S::MIR172 Expression of MIR172 at high levels in all cells prevents P2 function

24 Expression of a mutant form of P2 mrn that has reduced homology to MIR172 causes increased petal number and more floral whorls

25 MIR172 is expressed only in the inner whorls in lder floral primordia and reduces P2 protein levels Floral meristems Older, Stage 7 flower ontrol protein protein

26 MIR172 restricts P2 activity to the 1 and 2 whorl so that G expression is prevented in these whorls but can occur in whorls 3 and 4 Wild type 35S::MIR172 MIR172 P2 G sep pet stam carp MIR172 G MIR172 G carp stam stam carp 35S::P2* not recognised by MIR172 P2* MIR172 sep pet pet sep

27 Misexpression of or and in leaves is not sufficient to convert leaves to petals Wild-type function function 35S::P3 35S::PI 35S::P1 Suggests another floral-specific factor is absent in the leaves. This was not identified by initial genetic screens

28 More MDS box genes expressed in the flower Initially identified as homologues of G GL2, GL4, GL9 Renamed sepallata 1,2,3 Specific expression patterns in whorls 2,3,4, although GL2 and GL9 are also expressed in whorl 1 of younger flowers. Genes in red from ntirrhinum Genes in blue from rabidopsis

29 Inactivation of SEP1 SEP2 and SEP3 in triple mutants Were not identified in Original mutant screens ecause of redundancy etween proteins. Wild type sep pet stam carp sep1 sep2 sep3 sep sep sep sep

30 Misexpression of SEP1 P1 PI and P3 in leaves creates petals Plants carrying combination of 35S::P1 35S::SEP2 35S::PI 35S::P3 Therefore a combination of P1 PI P3 SEP is sufficient To confer function.

31 function DN function Open reading frame Model explains how function (P1) and function (P3/PI) ombine to specify the second whorl petals. Sepallata 1 and Sepallata 2 sep SUP Sepallata 3 pet stam carp

32 Similar multimeric complexes of MDS box proteins are proposed to specifiy the other whorls + function function + function function

33 SEP proteins mediate multimeric complexes between PI/P3 and G or between PI/P3 and P1 Wild type Sepallata 1 and Sepallata 2 sep SUP Sepallata 3 pet stam carp Formation of multimeric complexes suggests mechanism for combining / and / functions within the model.

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