Evolution of Flower Development Why are flowering plants so diverse? Using the Evo-Devo Approach to study floral diversity
Developmental processes that occur in the flowers 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 Mohavea confertiflora - Changes in symmetry with an evolutionary effect
Cubas (2004) Hileman et al. (2003) M. confertiflora mimics a radial species.
Mohavea confertiflora Mentzelia 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 sepals 'A' and 'B' genes in combination control the petals '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?