Outlines of five current research projects
1. Evolution and ecology of fast seed germination in Amaranthaceae s.l.
Several species of Chenopodiaceae and Amaranthaceae show very fast seed germination. Some species are able to germinate within a few hours and therefore are among the fastest germinating seeds in the plant kingdom. This project investigates seed and seedling traits as well as ecological conditions related to germination speed in c. 120 species of Chenopodiaceae and Amaranthaceae. We study the evolution and correlation of seed and germination traits in a phylogenetic context. We test the hypotheses whether fast germination represents an adaptation to stressful and dynamic environments and whether fast germination is achieved by a specific seed anatomy and morphology. Heterodiaspory is common in Chenopodiaceae and Amaranthaceae. We test the hypothesis if this trait evolved as an evolutionary rescue from the risk of fast germination.
Partners of this project:
Dr. F. Vandelook, Nationale Plantentuin von Belgie, Univ. Meise, Belgium.
Dr. R. Newton, Millennium Seed Bank, Kew, UK.
2. Evolution and ecology of C4 photosynthesis in succulent plant lineages
The evolution of C4 photosynthesis is a prime example of the convergent evolution of a complex trait showing significantly different patterns of evolution and intriguing ecological diversity in succulent plant lineages in comparison to grasses. Succulence in combination with C4 photosynthesis constitutes a key innovation of several plant lineages for evolutionary success in dry and saline habitats. However, it seems that C4 lineages share a genetic toolbox of household genes of which modified isoforms are repeatedly recruited into the C4 metabolic pathway. The efficient functioning of these C4 enzymes is dependent on their regulatory finetuning as they have to be expressed in the right place and amount.
Plant groups studied in this project are Camphorosmoideae, Salsoloideae and Salicornioideae (Chenopodiaceae), Sesuvioideae (Aizoaceae), Zygophylloideae and Tribuloideae (Zygophyllaceae). While in some groups we are still busy with identifying C4 species and C4 lineages and resolving their origin, we gain a deeper understanding of the structural, biochemical and genetic changes involved through sister group comparisons in others where phylogenetic relationships are clear. With the advances in our understanding of the genetic changes required for C4 photosynthesis in the recent past it becomes now feasible to study the evolution of gene regulation during the origin of the C4 pathway in these groups. We identified two promising study groups, Salsoleae (Chenopodiaceae) and Sesuvioideae (Aizoaceae), which both combine C4 photosynthesis and succulence, albeit with differences in age of the C4 lineages, biochemical subtype and anatomy, and some of which showing a developmental switch from C3 to C4 and other that show intermediate (C2) phenotypes. These two lineages are highly suitable to study the evolution of C4 genes and their possible regulatory genes. We hypothezise that in C4 species gene families of regulatory genes will include isoforms modified for their specific role in the C4 syndrome, we further believe to find C4 specific amino acid changes in these photosynthetic isoforms, we test whether expression level and pattern of the regulatory genes is correlated with their target C4 genes. With our young C4 lineages in Sesuvioideae and with our C3-C4 intermediate species in Salsoleae we test the hypothesis that gene regulatory changes (in other words genetic changes in the regulator genes of the C4 genes) preceed changes in the C4 genes themselves. The latter hypothesis will be tested in particular for the key enzyme of the C4 pathway, PEPC. The results of this project have strong implications for the current model of C4 evolution as well as for the evolution of complex traits in general. Furthermore, advances in our knowledge of the changes in gene regulators of C4 genes might be an important puzzle piece in the attempt to bioengineer C4 crops.
Partners of this project:
Prof. G. Edwards, School of Biological Sciences, Washington State University, USA
Dr. U. Gowik, Institut für Biologie und Umweltwissenschaften, Univ. Oldenburg
Prof. T. Hankeln, AG Molekularbiologie, iOME, Univ. Mainz
Prof. Jürgen Kesselmeier, Max-Planck Institut für Chemie, Mainz.
Prof. D. U. Bellstedt, Dept of Biochemistry, University of Stellenbosch, Stellenbosch, South Africa.
Prof. R. Sage and Dr. T. Sage, Dept. of Ecology and Evolutionary Biology, Univ. Toronto, Canada.
Prof. M. Ludwig, Biochemistry and Molecular Biology, Univ. of Western Australia, Perth, Australia.
Prof. E. Voznesenskaya and Dr. N. Koteyeva, Laboratory of Anatomy and Morphology, V. L. Komarov Botanical Institute of Russian Academy of Sciences, Saint Petersburg, Russia
Prof. P. Westhoff, Institut für Entwicklungs- und Molekularbiologie der Pflanzen, Univ. Düsseldorf, Germany.
3. Evolution and ecology of CAM photosynthesis in Crassulaceae and Aizoaceae
Crassulacean Acid Metabolism (CAM) is a photosynthetic pathway that allows plants to save water by assimilating CO2 during the night, when the evaporative demand of the atmosphere is lowest. CAM plants are nearly exclusively succulents, as they profit from a high malate storage capacity in their large vacuoles. Crassulaceae and Aizoaceae display examples for all sorts of CAM variations (e.g. obligatory CAM, CAM idling or CAM cycling), as well as C3 photosynthesis and intermediary or facultative forms between these types. Using the tribe Aeonieae (Crassulaceae) and Mesembryanthemoideae (Aizoaceae) as a model groups, our aim is to understand the evolution of this complex physiological trait which has allowed multiple individual lineages from at least 35 plant families to conquer new, especially carbon-deficient or dry habitats, and thus uniquely shape their environment.
Its eco-physiological diversity make the Macaronesian tribe Aeonieae (64 spp., 4 gen.) a perfect group to study the evolution of CAM in greater detail. Our aim is to combine data on the photosynthetic pathway, species distribution modelling and (micro)climatic data and a well-resolved molecular phylogeny to assess the hypothesis that CAM has enabled plants to thrive and diversify in environments with extensive periods of drought. Analysis of key genetic drivers for night-time carbon assimilation (PEPC, PEPC-K) will identify genetic and regulatory changes necessary for C3-CAM transitions. Special attention will have to be paid to the high potential of hybridization in this tribe. The question whether hybrids of CAM and C3 parent species engage in intermediate forms of photosynthesis may be elucidated in the same study group.
Partners of this project:
Dr. Ángel Bañares Baudet, Departamento de Biología Vegetal (Botánica), Universidad de La Laguna, Tenerife
Dr. Urs Eggli, Sukkulenten-Sammlung Zürich, Zürich, Switzerland
Prof. C. Klak, Dept. of Biological Sciences, Univ. of Cape Town, Rondebosch, Cape Town, S. Africa
Dr. Stephan Scholz, Jardín Botánico Fuerteventura Oasis Park, Canary Islands
4. Diversification of Australian Chenopodiaceae as dominant flora elements of the arid biomes
Unresolved phylogenetic trees in young, rapidly diversified and species-rich lineages are a common problem in molecular systematics and in many cases urgently needed taxonomic revisions in these groups are postponed to the undetermined future until a more substantial phylogenetic hypothesis for the respective lineage will become available. Insufficient systematic and taxonomic treatments especially of key elements of the flora such as Chenopdodiaceae in arid biomes of Australia hamper ecological and biodiversity research. We currently explore a modified ddRadSeq protocol for its potential to resolve phylogenetic relationships in rapidly diversified lineages using long and informative loci for gene tree/species tree inferences. The study groups are the rapidly diversified and species-rich Australian Camphorosmeae (bluebush) and Australian Atriplex which are both widely distributed in arid and saline environments of the continent. Fruit morphology is exceedingly diverse in Camphorosmeae and Atriplex and diagnostic at species level, at the same time fruit traits are highly adaptive. Therefore, based on the phylogeny we will analyse the evolution of fruit traits in relation to range expansion and habitat shifts using the wealth of collection data available through online databases.
Partners of this project:
John McDonald & Prof. A. Lowe, School of Earth and Environmental Sciences in the Faculty of Science, University of Adelaide, Australia
Dr. Margaret Byrne, Dr. Kelly Shepherd and Dr. Terry Macfarlane, Western Australian Herbarium at the Department of Parks and Wildlife (Perth)
5. Biodiversity of African and Madagascan Melastomataceae
Melastomataceae are the seventh most diverse angiosperm family in the world (172 gen., ca. 5100 spp.) and widely distributed in tropical regions worldwide. Melastomes are easy to recognize by their acrodromous leaf venation and colourful flowers with conspicuous stamens. The family is ubiquitous and highly diverse in various vegetation types of tropical Africa and Madagascar, however, our knowledge of their diversity is fragmentary, their patterns and drivers of diversification are unstudied and their current naming is highly artificial. Therefore, we investigated the molecular phylogeny and diversification of Melastomateae, the most diverse tribe in Africa (ca. 185 spp. in 13 gen.), and proposed a fundamentally new classification of the tribe with many new genera and species. Biogeographcal analyses revealed a South American origin of the tribe and multiple dispersal events to Madagascar and a single dispersal event to South East Asia. Also, several habitat shifts from closed to open habitats during the Miocene and a rapid change of stamen morphology were discovered. We are currently completing the phylogeny of Melastomateae with emphasis on the so far poorly sampled Madagascan species and resolving the generic relationships of African/Madagascan Sonerileae (ca. 160 spp. in six genera), also providing an updated classification for this tribe, and aim at comparative analyses of the biogeography as well as the morphological and ecological diversification of both tribes. Currently, only four species of African/Madagascan Sonerileae have been sampled in molecular studies, and these form a monophyletic group with some Asian Sonerileae. However, whether the African/Madagascan Sonerilean genera and the subgenera and sections of the large genus Gravesia are monophyletic lineages is unknown. Through a careful morphological, geographical survey of these lineages based on the study of herbarium specimens and a molecular phylogenetic study we will be able to comprehensively study the diversity and diversification of these two tribes and provide vital data towards a complete understanding of the evolution and systematics of the entire African and Madagascan Melastomataceae. In addition, a comparative study of biogeography and trait evolution in Melastomateae and Sonerileae will provide answers regarding diversification in relation to their divergent ecology, habitat and pollination biology with implications for the mega-diverse Melastomataceae as a whole. Our phylogenetic and morphological results will be used for providing an updated classification of African/Madagascan Melastomateae and Sonerileae, they will have a strong and direct impact on floristic treatments of the family, e.g. the on-going Flora of Central Africa and updating the Floras of Gabon and Cameroon, and results in taxonomic revisions of several genera.
Partners of this project:
Dr. M.-C. Veranso-Liballah, Mainz, Germany (postdoc in my group)
Dr. T. Couvreur, Yaoundé, Cameroon und Montpellier, France
Dr. D. Stone, Kwa Zulu Natal, South Africa
Dr. F. Almeda & Dr. H. Ranarivelo, San Francisco, USA