Evolution of Development Why are flowering so diverse? Using the Evo-Devo Approach to study floral diversity

Developmental processes that occur in the different taxa.

Infer evolutionary events that led to the differences or similarities.

Zahn et al. (2005) Floral diversity is generated by different mature morphologies

Phyllotaxy

Symmetry

Organ Fusion

Whorl Number

Organ Elaboration

Organ Identity Floral Symmetry Reverse Genetics - Floral Symmetry controlled by CYCLOIDEA(CYC) and DICHOTOMA(DICH) Antirrhinum majus WT Peloric

CYC expression in developing flowers

Luo et al. (1996) Bilateral Symmetry has evolved many times

Carl Linneaus 1707-1778

Linaria vulgaris peloric mutant Linaria vulgaris

Forward genetics - L. vulgaris peloric mutations caused by methylation of CYCLOIDEA - Changes in symmetry with an evolutionary effect

Cubas (2004) Hileman et al. (2003) M. confertiflora mimics a radial species.

Mohavea confertiflora involucrata Floral Organ Identity

Sepal – 1st Whorl

Petal – 2nd Whorl

Stamen – 3rd Whorl

Carpel – 4th Whorl Floral Organ Identity genes are MADS Box genes = Transcription Factors

HOX Genes

MADS-Box genes in flowers are HOX genes in animals are important for important for correct organ identity. correct body-plan formation. “ABC” Model of Flower Development

Arabidopsis thaliana Antirrhinum majus

'A' genes control the 'A' and 'B' genes in combination control the 'B' and 'C' genes in combination control the stamens 'C' genes control the carpels

Homeotic Mutants – used to study HOX genes in Drosophila

WT

HOX Genes

antennapedia

Carroll et al. (2005). Homeotic conversions of floral organs to study gene function in flower development

C-class gene in Arabidopsis = AGAMOUS “Sliding Boundary” model is one modification to the ‘ABC’ Model

B B B

A C

SPSEEEPTP SPPEEEPTT STA C A R

Kramer et al. (2003) T. thalictroides Horticultural Mutants

Wildtype ‘Betty Blake’ ‘Shoaf’s Double’

‘Green Dragon’ ‘Double White’ Double Flowers – the first recorded floral mutants

T. thalictroides T. thalictroides WT ‘Double White’

Theophrastus 371-287 BC

Arabidopsis Arabidopsis WT agamous mutant Thalictrum C-class genes

2 AGAMOUS (AG) orthologs: ThAG1 and ThAG2

ThdAG1 carpellate flower

ThdAG1 staminate flower

ThdAG2 carpellate flower

Di Stilio et al. 2005 Kramer et al. 2004 Forward Genetics – ‘Double White’ has a defect in ThAG1

T. thalictroides T. thalictroides WT ‘Double White’ Reverse Genetics – Down-regulating ThAG1 creates a ‘double flower’ phenotype

Viral Induced Gene Silencing (VIGS)

T. thalictroides WT

T. thalictroides ‘Double White’

T. thalictroides TRV2ThAG1 Conclusions from the DW/ThAG1 story:

ThAG1 function is conserved.

The double-flower phenotype in ‘Double White’ does result from a mutation in the AGAMOUS ortholog.

Evolutionary benefit?