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Plant growth and proliferation control is coming into a global focus due to recent ecological and economical developments. Plants represent not only the largest food supply for mankind but also may serve as a global source of renewable energies. However, plant breeding has to accomplish a tremendous boost in yield to match the growing demand of a still rapidly increasing human population. Moreover, breeding has to adjust to changing environmental conditions, in particular increased drought. Regulation of cell-cycle control is a major determinant of plant growth and therefore an obvious target for plant breeding. Furthermore, cell-cycle control is also crucial for the DNA damage response, for instance upon irradiation. Thus, an in-depth understanding of plant cell-cycle regulation is of importance beyond a scientific point of view. The mere presence of many conserved core cell-cycle regulators, e.g. CDKs, cyclins, or CDK inhibitors, has formed the idea that the cell cycle in plants is exactly or at least very similarly controlled as in yeast or human cells. Here together with a recent publication we demonstrate that this dogma is not true and show that the control of entry into mitosis is fundamentally different in plants versus yeast or metazoans. Our findings build an important base for the understanding and ultimate modulation of plant growth not only during unperturbed but also under harsh environmental conditions.
Publications
Oxidative tailoring of C40 carotenoids by double bond-specific cleavage enzymes (carotenoid cleavage dioxygenases, CCDs) gives rise to various apocarotenoids. AtCCD1 generating C13 and C14 apocarotenoids and orthologous enzymes in other plants are the only CCDs acting in the cytosol, while the hitherto presumed C40 substrate is localized in the plastid. A new model for CCD1 action arising from a RNAi-mediated CCD1 gene silencing study in mycorrhizal hairy roots of Medicago truncatula may solve this contradiction. This approach unexpectedly resulted in the accumulation of C27 apocarotenoids but not C40 carotenoids suggesting C27 as the main substrates for CCD1 in planta. It further implies a consecutive two-step cleavage process, in which another CCD performs the primary cleavage of C40 to C27 in the plastid followed by C27 export and further cleavage by CCD1 in the cytosol. We compare the specificities and subcellular locations of the various CCDs and propose the plastidial CCD7 to be the first player in mycorrhizal apocarotenoid biogenesis.
Publications
In Arabidopsis thaliana, mitogen activated protein kinase (MAPK) signaling cascades that contain MPK3, MPK4 and MPK6 have been implicated in various aspects of developmental processes and stress responses. We identified an ethylene response factor (ERF104), which controls innate immunity, to be a specific substrate of MPK6 and showed that ethylene signaling regulates the release of the ERF104 substrate from its kinase. Implications and questions that arise from our findings are addressed. To promote discussions, previously unpublished data, that are rather confounding, are presented and possible explanation provided on how these may fit into our current model.
Publications
The mutualistic interaction of plants with arbuscular mycorrhizal (AM) fungi is characterized by an exchange of nutrients. The plant provides sugars in the form of hexoses to the heterotrophic fungus in return for phosphate as well as nitrogen, water, and micronutrients. Plant sucrose-cleaving enzymes are predicted to play a crucial role in hexose mobilization as these enzymes appear to be absent in the fungal partner. Here, recent findings concerning the function of plant apoplastic invertases in the AM symbiosis are discussed. Plants with modulated enzyme activity in roots and leaves provide additional insight on the complexity of the regulation of the AM interaction by apoplastic invertases as mycorrhization could be reduced or stimulated depending on the level of invertase activity and its tissue-specific expression.