Chlorinated auxins–how does Arabidopsis thaliana deal with them?

Plant hormones have various functions in plants and play crucial roles in all developmental and differentiation stages. Auxins constitute one of the most important groups with the major representative indole-3-acetic acid (IAA). A halogenated derivate of IAA, 4-chloro-indole-3-acetic acid (4-Cl-IAA), has previously been identified in Pisum sativum and other legumes. While the enzymes responsible for the halogenation of compounds in bacteria and fungi are well studied, the metabolic pathways leading to the production of 4-Cl-IAA in plants, especially the halogenating reaction, are still unknown. Therefore, bacterial flavin-dependent tryptophan-halogenase genes were transformed into the model organism Arabidopsis thaliana. The type of chlorinated indole derivatives that could be expected was determined by incubating wild type A. thaliana with different Cl-tryptophan derivatives. We showed that, in addition to chlorinated IAA, chlorinated IAA conjugates were synthesized. Concomitantly, we found that an auxin conjugate synthetase (GH3.3 protein) from A. thaliana was able to convert chlorinated IAAs to amino acid conjugates in vitro. In addition, we showed that the production of halogenated tryptophan (Trp), indole-3-acetonitrile (IAN) and IAA is possible in transgenic A. thaliana in planta with the help of the bacterial halogenating enzymes. Furthermore, it was investigated if there is an effect (i) of exogenously applied Cl-IAA and Cl-Trp and (ii) of endogenously chlorinated substances on the growth phenotype of the plants

Assessing the Conditions for Multilateral Interventions or Non-Interventions: Intervention and Non-Intervention in the Asia Pacific Region

The focus of this thesis has been on the identification of the primary conditions that attract or deter multilateral interventions into internal conflicts in the Asia Pacific region. This thesis develops a framework which is applied to four cases of internal conflict to see what roles twenty-two structural and perceptual conditions have played in determining why multilateral intervention was initiated in two of the cases, and why multilateral intervention failed to be initiated in the other two cases. The research found that multilateral organizations will accept risks and costs associated with intervention if certain structural and perceptual conditions make intervention an attractive option. These conditions are, a favourable or significant international environment or international event(s), the consent of a sovereign state (even if it is induced), sustained and critical regional and international media coverage, a complete collapse of the state in conflict tainting it with the term 'failed state', a high probability of success, potential economic benefits, a humanitarian crisis (in respect of Unregulated Population Movements and genocide/politicide), the possibility of a clear exit strategy, and a self-interested Member State who can greatly subsidize an intervention. Multilateral non-interventions, on the contrary, are driven by a combination of a lack of sustained and critically analyzed media coverage on conflict issues and consequences, generally positive tactics and strategies adopted by disputants, conflicts of a long duration, the international environment, economic factors unfavourable to intervention, resistance levels to intervention or a failure to call for intervention, lack of any clear exit points, and an escalation phase. The importance of these conditions suggest that multilateral organizations are reluctant to take risks and costs when political will, for the collective and self, are not provoked. Consequently, particular structural and perceptual conditions trigger or influence political will. The analysis of four case studies (East Timor, Solomon Islands, Philippines (Moros), and West Papua) concludes that multilateral interventions will be the exception to the rule in the foreseeable future given the obvious selection bias evident in these policies, and the project questions the ad hoc determinants of current multilateral intervention policies

A role for the cell-wall protein silacidin in cell size of the diatom Thalassiosira pseudonana

Diatoms contribute 20% of global primary production and form the basis of many marine food webs. Although their species diversity correlates with broad diversity in cell size, there is also an intraspecific cell-size plasticity due to sexual reproduction and varying environmental conditions. However, despite the ecological significance of the diatom cell size for food-web structure and global biogeochemical cycles, our knowledge about genes underpinning the size of diatom cells remains elusive. Here, a combination of reverse genetics, experimental evolution and comparative RNA8 sequencing analyses enabled us to identify a previously unknown genetic control of cell size in the diatom Thalassiosira pseudonana. In particular, the targeted deregulation of the expression of the cell-wall protein silacidin caused a significant increase in valve diameter. Remarkably, the natural downregulation of the silacidin gene transcript due to experimental evolution under low temperature also correlated with cell-size increase. Our data give first evidence for a genetically controlled regulation of cell size in Thalassiosira pseudonana and possibly other centric diatoms as they also encode the silacidin gene in their genomes