Reaching for the sky: exploring massive convergent evolution towards woodiness in Brassicaceae

• Applicant: Professor Dr. Klaus Mummenhoff
• Subject Area: Evolution and Systematics of Plants and Fungi
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 418452287

Woody plants (trees and shrubs) cover 30 percent of the planet's land area and offer crucial ecosystem services, such as buffering climate change by storing carbon from the atmosphere. It is unclear, however, why some plants are woody and others herbaceous. This seemingly simple question intrigued Charles Darwin when he visited oceanic islands in the 1830s, and he used the term ‘insular woodiness’ (later rephrased to the broader term ‘derived woodiness’) for woody flowering plant species that have evolved from herbaceous relatives that in turn originated from ancestrally woody species. To this day, scientists have failed to provide satisfying answers why derived woodiness have occurred hundreds of times during evolutionary history of flowering plants, probably because wood formation is a complex process that can be triggered in different and largely understudied ways. Solving this long-standing question requires an innovative multidisciplinary approach, linking evolutionary and ecological models. The cosmopolitan mustard family (Brassicaceae, 4000 species) serves as an excellent model group to understand wood formation due to the occurrence of many crops and model species, and the remarkable number of evolutionary transitions towards the derived woody growth form. Ten percent of the Brassicaceae species are woody – reaching up to 9m tall – and woodiness has evolved probably more than 100 separate times in contrasting environments on both islands and continents, which is extraordinary for a single family. However, deep phylogenetic relationships within Brassicaceae remain poorly understood, thereby impeding evolutionary questions at the family level. This proposal focuses on three main objectives: (1) accurately assess the number of transitions towards woodiness in Brassicaceae based on a (time-calibrated) family phylogeny using hybridization sequencing of 1000 carefully selected species, (2) test the impact of woodiness as potential driver for species diversification across the 100+ clades including woody Brassicaceae, and (3) determine the correlation between woodiness versus (palaeo)climate and soil variables in these clades. Outcomes of this project will revolutionize our understanding of wood formation, bridge the gap between evolutionary biologists and ecophysiologists, and provide a robust phylogenetic framework that will serve the entire Brassicaceae community for the coming years. Moreover, the proposed work on wood evolution can open up new opportunities for developmental genetists who will be able to search for the key regulatory genes that turn on the wood pathway in many woody-herbaceous sister pairs that are all closely related to Arabidopsis.

• DFG Programme: Research Grants
• International Connection: Netherlands, Sweden, USA
• Co-Investigator: Professor Dr. Stefan A. Rensing
• Cooperation Partners: Professor Ihsan Al-Shehbaz, Ph.D.; Professor Frederic Lens, Ph.D.; Professor Lachezar Nikolov, Ph.D.; Professor Dr. Alexander Zizka