Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - CAPITULA (Variation on a theme: evolutionary-developmental insights into the Asteraceae flower head)

Teaser

The Asteraceae, or daisy family, is the most species-rich family of all flowering plants and is one of the dominant families represented in many threatened ecosystems such as the grasslands and the high-altitude mountains. The family is characterised by its peculiar...

Summary

The Asteraceae, or daisy family, is the most species-rich family of all flowering plants and is one of the dominant families represented in many threatened ecosystems such as the grasslands and the high-altitude mountains. The family is characterised by its peculiar inflorescence –the capitulum– which mimics a flower but is in fact composed of a multitude of tightly grouped florets. The capitulum is seen as a key innovation that has greatly contributed to the impressive evolutionary success of the family. It also participates in the family’s economic success, since many species are cultivated for their capitulum for agricultural (e.g. the sunflower, the artichoke) and horticultural (e.g. Chrysanthemum, Gerbera) purposes. However, to date, there is still no comprehensive understanding of how the capitulum originated and how its morphology and structure varies across the Asteraceae. This is mainly due to a lack of appropriate tools for describing such a complex and condensed structure, together with the practical and analytical challenges of compiling (i.e. the data collection itself) and analysing very large datasets. CAPITULA focuses on syncephalous Asteraceae, which represent a model system specifically targeted –and uniquely suited– for studying inflorescence complexity in Asteraceae. While most species have a simple capitulum, in a few species the inflorescence is more complex as it is formed by bringing together multiple capitula to form a secondary capitulum (=syncephalia). Syncephalous species constitute invaluable material for deciphering the genetic basis and evolutionary origin of the capitulum because their genomes have undergone the inflorescence shift toward capitulescence twice thus allowing the genetic signature of capitula formation to be recovered twice. Our approach, integrating the most recent experimental and theoretical developments in evo-devo and genomics fields, provides a unique opportunity to ask fundamental questions relating to coordinated trait evolution, and to increase our understanding of how genetic pathways have been altered or co-opted during the evolutionary diversification of flowers

The clustering of flowers into inflorescences is a major recurrent evolutionary trend associated with pollinator attraction that has played an important role in the diversification of angiosperms. Research on the origin and evolution of inflorescence diversity is of prime importance when considering that much of our food relies on seed and fruit crops. Indeed, inflorescence structure determines the number and arrangement of flowers and fruits, and is thus vital for reproductive fitness and constitutes a key character for plant domestication and crop production.

CAPITULA’s main objectives are to: 1–Explore the morphological landscape of Asteraceae inflorescences, and provide insights on the biological and evolutionary significance of capitulum diversification in Asteraceae, 2–Identify the origin and assembly of the genetic pathways subtending inflorescence transitions and 3–Investigate the genomic changes (e.g. polyploidization, genome size shifts, transposable element activity) associated with capitulum evolution.

Work performed

The fellow has taken full advantage of her MSCA fellowship which has enabled her to deliver novel data for each of the three work packages as well as to ensure the data are widely disseminated to broad general and scientific audiences. She has also generated additional data that lay the foundations for further research in this novel research area she has established, and these will continue to generate further opportunities for dissemination and exploitation in the forthcoming years. She embarked on the challenging task of developing a typology suitable for characterising the inflorescence of any of the c. 25,000 Asteraceae species. To gather inflorescence data on a large number of species she trained a postdoctoral fellow Lin Fu (Chinese Academy of Sciences) and two summer students Benjamin Coquillas and Clément Vignon (ENSEIRB-MATMECA, Bordeaux Graduate School of Engineering, France), to assist with the inflorescence phenotyping. She did a field trip in Patagonia with Cynthia González (Universidad San Juan Bosco, Argentina) to gather inflorescence data on early diverging Asteraceae. Furthermore, the fellow co-led the project “Ain’t no mountain high enough: evolution of Asteraceae in the European Alps” (Kew Foundation), which has generated a large amount of inflorescence data for alpine Asteraceae. As a result, information for c. 700 species are now available. In parallel, the fellow contributed to ‘The Plant and Fungal Trees of Life project (Royal Botanic Gardens, Kew)’ with the proposal “The hyper-diverse family Asteraceae: Functional and evolutionary insights” which aims to build a robust phylogenetic framework across Asteraceae by generating phylogenomic data for >1000 genera. A robust phylogenetic backbone is essential to accurately model trait evolution and test hypotheses regarding inflorescence evolution within the family. It is anticipated that phylomorphospace analyses on the inflorescence data gathered during CAPITULA will provide distinctive new insights into the biological and evolutionary significance of capitulum diversification in Asteraceae. The fellow has also established strong collaborative links with the Gerbera team (University of Helsinki, Finland) enabling the sequencing of the transcriptome of two syncephalous Asteraceae whose analysis will provide insights on the genes putatively involved in inflorescence architecture. She has also initiated a collaboration with Sébastien Lavergne (Laboratoire d’Ecologie Alpine, Grenoble, France), that will allow the analyses of repetitive sequences to be extended to include a much larger sample of Asteraceae species than originally planned and covering a wide array of inflorescence morphologies. The extensive survey of genome sizes in Asteraceae (c. 700 new values assessed) has revealed a moderate range of genome size variation and suggests that shifts to syncephaly are likely to be associated with changes in genome size arising from whole genome duplication events. The fellow has presented CAPITULA’s preliminary results in a diverse array of outreach activities to the general public, such as the Kew Science blog “Effeuillons la marguerite (let’s pluck the daisy)”, and to a diverse scientific audience through talks in seminars and at congresses. There is no doubt that this research will lead to an increased understanding of evolutionary diversity and genomic processes underlying inflorescence evolution in Asteraceae, and that the results will be published in the most competitive journals.

Final results

CAPITULA focuses on floral architecture, a major trait that has been under selection throughout angiosperm diversification. The research undertaken has increased our understanding of the evolutionary diversity and genomic processes underlying the evolution of this key floral trait in Asteraceae. Such new understanding is particularly important for many poorly studied syncephalous Asteraceae genera as most comprise a single species, hence any loss due to global change will lead to the rapid erosion of diversity at the genus level. Finally, by being the family with the greatest number of species, Asteraceae are of major economic and ecological importance which makes their study essential for understanding their contribution to ecosystem services and their management.

Website & more info

More info: https://www.kew.org/science/projects/capitula.