Plant regulatory networks
Plastids have a tremendous importance in plants as they are the photosynthetic organelles. But their importance extends way beyond this physiological role, as they are also part of the regulatory network that controls the life cycle of the entire plant. Our research is focussed on the integration of the cell organelles (plastids as well as mitochondria) into cellular response regulation of plants with a particular focus on dually targeted proteins.
Being stationary organisms, higher plants have no chance to escape a changing environment, making it important for them to have an early and sensitive cellular alarm system that allows them to react to environmental stress.
Plastids seem to play a key role in this stress perception and response system, for obvious reasons: they harbour some of the most important and most sensitive metabolic processes such as photosynthesis.
At the same time, they are intimately connected to the cell’s command centre, the nucleus, as all metabolic reactions in chloroplasts are dependent on both, nuclear-encoded and plastid-encoded genes. Therefore, these energetic organelles can be assigned a key role in ensuring a coordinate expression of nuclear and organellar genes.
Dual targeting into chloroplasts and the nucleus
Dually targeted proteins that locate to the nucleus as well as to plastids(pnDTPs=plastid/nuclear dually targeted proteins) are believed to play a vital role in the communication between these compartments. The first pnDTP that was located in both compartments of the same plant cell was the Whirly1 protein. Bioinformatic and experimental analyses revealed meanwhile that a larger number of DNA-binding proteins with dual targeting properties exist.
Several of these proteins from Arabidopsis, among them the Whirly proteins, two AP2 proteins and some C3H and bHLH proteins are under investigation in our lab in order to investigate the significance of dual targeting for plant development and stress response.
Reverse genetics and the generation of single targeted (partial) mutants are employed to assess the proteins’ roles in regulating gene expression in the two compartments while fluorescent protein tagging technology and biochemical methods are used to unravel the localisation of the proteins and their interaction partners.
Dual targeting into chloroplasts and mitochondria
Dually targeted proteins were found in species across the plant kingdom from single celled organisms to seed plants.
An intriguing question is, therefore, whether the target peptides that confer the targeting properties were conserved during the evolution of the plants or whether they have evolved separately and with different specificity and sensitivity.
In order to elucidate this question, we are taking advantage of two model organisms separated by ca. 450 Ma of divergent evolution: the seed plant Arabidopsis thaliana and the moss Physco-mitrella patens.
Plastid/mitochondrial but also plastid/nucleus targeting properties of proteins from each species are tested experimentally in the other respective model system and the results are compared with the expectations raised by different prediction programs that were trained with proteins from either of these species.