1. DORMANCY REGULATION IN LAND PLANTS BY EVOLUTIONARILY CONSERVED MECHANISMS
The biology of Marchantia polymorpha and related liverworts has fascinated botanists for centuries, providing a rich literature describing both phenomenology and pharmacological experiments. With the advent of Marchantia as a model genetic system, we are now in a position to begin to elucidate the molecular genetic mechanisms by which its architecture, development and growth is regulated. We are tracing the evolutionary history of genetic programs for dormancy regulation initially identified in seed plants by examining them functionally in Marchantia. We are also screening for novel dormancy regulators. Dormancy was a key adaption to facilitate survival in terrestrial environments, enabling seasonal growth. Understanding dormancy regulation in liverworts will aid efforts to decipher the evolution of dormancy leading to the adapted forms seen in flowering plants. Marchantia is emerging as a powerful model species. This unique plant has low genetic redundancy, and many molecular tools are available, including a sequenced genome (See Bowman et al., 2017). In the long term, this project poses two interrelated questions: 1) how similar are the genetic programs for developmental processes in evolutionarily distant plants, and 2) how can we exploit the simplicity of the Marchantia model system to help decipher the complexity of flowering plants? In this project we are studying the differences and similarities in dormancy regulation between the liverwort Marchantia and seed plants such as Arabidopsis. This involves examination of genetic and hormonal pathways for phytohormones such as auxin and abscisic acid, and will lay a foundation for the discovery of previously uncharacterized evolutionarily conserved components regulating plant development. A detailed understanding of plant development is of great importance not only for basic sciences - knowledge about the integration of developmental pathways is also critical to facilitate the precise design of plants for diverse agricultural applications. The specific aims of this project are to: 1) Identify and characterize the interaction between different hormonal pathways for dormancy regulation in Marchantia, 2) and to identify and characterize novel regulators of dormancy in land plants.
A recent publication from this project is Eklund et al., 2018, Current Biology.
2. THE LAND PLANT CIRCADIAN CLOCK
Adaptation to changing environments is critical to all life. Some of these changes are predictable such as day/night cycles and the ever-changing seasons. Accordingly, organisms from all kingdoms of life have developed mechanisms to anticipate such predictable changes. Intrinsic clocks that generate circadian rhythms are present in most organisms, from cyanobacteria to land plants and animals. Although the overall architecture is generally conserved, the key genes involved are generally not, suggesting multiple independent origins of circadian clocks.
The plant circadian clock is a self-sustaining oscillator and the approximately 24-hour rhythm results mainly from transcriptional and translational feedback loops. Angiosperm clocks can be described as an intricate network of interlocked feedback loops, but clocks of green algae have been modelled as a loop of only a few genes. To investigate the evolution from a simple clock in algae to a complex one in angiosperms, we are performing phylogenetic and functional studies of circadian clock genes in bryophyte model species, such as Marchantia polymorpha.
For more information on this project, see our recent publications Early evolution of the land plant circadian clock, Linde et al., 2017, New Phytologist and Nyctinastic thallus movement in the liverwort Marchantia polymorpha is regulated by a circadian clock.
3. Evolution and function of the shoot apical meristem
We aim at elucidating some of the differences and similarities in shoot meristem function between the flowering plant Arabidopsis, and the liverwort Marchantia. Among our objectives are studies of transcription factor networks in Marchantia, which will lay a foundation for the discovery of previously uncharacterized mechanisms regulating plant development and architecture. This is of great importance in a longer perspective, as knowledge about the integration of the environment and genetic pathways is critical to facilitate the precise design of plants for diverse agricultural applications in a world with an unstable climate and a growing population.
Extreme low light conditions appear to force the Marchantia shoot meristem to revert to a juvenile undifferentiated developmental stage. This phenotype can be mimicked by constitutive expression of a single gene, suggesting this gene to have a key role in light-regulated developmental transitions. This gene's relation to light, hormonal pathways and differentiation of the apical cell will be examined using molecular methods with the aim to find direct downstream targets as well as regulators.