Evolution and Development of Flower Diversity Kelsey Galimba Di Stilio Lab Department of Biology University of Washington Lecture Outline Evolution of Angiosperms •! The first flower •! Morphological Diversity Development •! “Evo-Devo” •! “ABC” Model Di Stilio Lab Research •! Thalictrum as a model system •! C Function Evolution of Angiosperms What is an Angiosperm? Derived Characteristics •! Wood with vessels •! Double fertilization - endosperm •! Pollen with columnar structures •! Angiosperm = “enclosed seed” – ovules enfolded within and protected within two layers. •! Flowers! – both reproductive organs on the same shoot. Seeking the First Flower Magnoliaceae - current Archaefructas - 144 mya? Fossil grass flower – 94 mya 2.2 mm. Seeking the First Flower Amborella trichopoda “The most similar living flower to the world’s first flower” – Jim Doyle, UC Davis - Dioecious -!2 whorls of undifferentiated sepals/petals -!Organs arranged in a spiral -!Indeterminate numbers or organs Darwin’s “Abominable Mystery”! How can angiosperms be so diverse?! When did Angiosperms Originate? Floral diversity is generated by varying many aspects of floral development, including: Symmetry Phyllotaxy Organ Organ Fusion Identity Merosity Whorl Organ Number Elaboration Evo-Devo: The Components Evolution Development Three principles: The process of growing to maturity. Variation Floral Development – The Heredity initiation of the floral meristem to the mature flower. Natural Selection Evo-Devo: The Logic •! Morphology is the product of development. •! Development is the product of genetic regulatory programs. •! Evolution of diversity (morphology) is directly related to the evolution of genetic regulatory programs. •! A limited number of genetic pathways have been used and re-used to build different body plans. Evo-Devo: The Questions! How are different taxa related phylogenetically? What kind of developmental traits did the ancestor have? How did developmental processes evolve? Flower Development Model Plants Arabidopsis thaliana! Antirrhinum majus! “ABC” Model of Flower Development '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 ABC genes are MADS Box genes = Transcription Factors Transcription Factors control expression levels of genes. HOX Genes MADS-Box genes in flowers are HOX genes in animals are important for important for correct organ identity. correct body-plan formation. Homeotic Mutants From Carroll S.et al , 2005. From DNA to diversity Homeotic conversions of floral organs to study gene function. “Sliding Boundary” model and predicted floral phenotypes! B B B A C SEPPETPETSEPSEP PET SEPPETPETPET STA CAR Kramer, E. M., V. S. Di Stilio and P. Schluter. 2003. Complex patterns of gene duplication in the APETALA3 and PISTILLATA lineages of the Ranunculaceae. Int. J. Pl. Sci. 164 (1): 1-11.! Extended “ABC” Model – A, B, C, D, and E genes Arabidopsis E mutant -ABC mutant? “Alles et Blatt” -!Johann Wolfgang von Goethe Land Plant “ABCs” A lineage Floral homeotic gene lineage established (B,C,E) Back to the First Flower - Gymnosperms have reproductive organs on different shoots. Most angiosperms have flowers that are hermaphroditic – on the same shoot “Mostly Male Hypothesis” - Possible ectopic expression of C genes on a male shoot to form the first hermaphrodite. 2007 Gerhard Leubner – The Seed Biology Place Di Stilio Lab Research Thalictrum Ranunculaceae Floral diversity in genus Thalictrum T. rochebrunianum T. alpinum T. kiusianum T. aquilegifolium T. dasycarpum •! 190 species •! Herbaceous perennials with nectarless, apetulous flowers •! Variability of perianth type •! Unisexual flower development without selective abortion of organs •! 4 Breeding systems: hermaphroditic, dioecious, andromonoecious, gynoecious •! 2 pollination mechanisms: insect and wind •! Pivotal phylogenetic position Geographic distribution of Thalictrum "#$%$&'()*+,!'-!.+-)/!011(233www.eol.org Evolution of Pollination dasycarpum Syndromes revolutum coriaceum Dioecy pubescens Combined ITS rpl16 cooleyi ? delavayi minus flavum ramosum ? aquilegifolium grandifolium? tripeltiferum ? Andromonoecy decipiens alpinum petal loss fendleri ? polycarpum Dioecy dioicum Pollination sparsiflorum thalictroides Insect clavatum Mixed Paraquilegia Leptopyrum Wind Enemion Unknown Aquilegia Brunnet & Liston Thalictrum by Pollination Type 456"78! 9:8;! <45=! T.rochebrunianum T. thalictroides T. pubescens T. fendleri! T. arsenii ! ! T.aquilegifolium T. delavayi T. flavum T. guatemalensis T. hernandezii T. uchiyamai! T. alpinum T. dasycarpum! Thalictrum thalictroides Anemonella thalictroides Rue-Anemone •! Geographic distribution: Eastern US •! Breeding System: Hermaphroditic •! Pollination System: Insect T. thalictroides Horticultural Mutants Wildtype ‘Betty Blake’ ‘Shoaf’s Double’ ‘Green Dragon’ ‘Double White’ Model System: Thalictrum What we study: MADS-box Transcription Factors AKA: Organ Identity Genes AKA: ‘ABC’ Genes Why? Studying the genes that control organ identity and development in a basal eudicot can shed light on how developmental processes in core eudicots evolved. Duplication events are common in MADS-box genes. This allows for sub and neo-functionalization which is theorized to create diversity. Duplication in C-function gene, AGAMOUS Thalictrum has 2 AGAMOUS (AG) orthologs: ThAG1 and ThAG2 ThAG2 falls within the AG (C-class) lineage, not the AGL 11 (D- class lineage) >,0#!)1!,&?!@AAB! ABC Model In Arabidopsis, AG is expressed in stamens and carpels. In Thalictrum, AG1 is expressed in stamens and carpels, AG2 expression is limited to ovules . Ovules AG2 Expression T. diocum VIGS – Viral Induced Gene Silencing Burch-Smith TM, et al. 2004 •!Uses the plant antiviral defense system - Post Transcriptional Gene Silencing (PTGS) •!Homology dependent sequence specific degradation of mRNA Phytoene Desaturase (PDS) as a marker for silencing Carpels in WT T. thalictroides are green ThAG1 silencing in Thalictrum results in the same phenotype as the Arabidopsis ag mutant. Arabidopsis WT Arabidopsis ag mutant T. thalictroides WT T.thalictroides AG-1 VIGS TthAG2_PDS VIGS Molecular Validation Downregulation of ThAG2 RT AG-2 Expression Actin Expression ThAG-2 VIGS Untreated ThAG-2 VIGS Untreated Do ThAG-2 silenced carpels have defective ovules? WT Scanning Electron Microscopy Ovules WT TthAG2 VIGS Confocal Microscopy Ovules The End .