Brassinosteroids Affect the Symbiosis Between the AM Fungus Rhizoglomus irregularis and Solanaceous Host Plants

Together with several proteins involved in brassinosteroid (BR) signaling and synthesis, the membrane steroid binding protein 1 (MSBP1) was identified within the interactome of the sucrose transporter of tomato (SlSUT2). We asked whether MSBP1 is also involved in BR signaling as assumed for the AtMSBP1 protein from Arabidopsis and whether it impacts root colonization with arbuscular mycorrhizal (AM) fungi in a similar way as shown previously for SlSUT2. In addition, we asked whether brassinosteroids per se affect efficiency of root colonization by AM fungi. We carried out a set of experiments with transgenic tobacco plants with increased and decreased MSBP1 expression levels. We investigated the plant and the mycorrhizal phenotype of these transgenic plants and tested the involvement of MSBP1 in BR metabolism by application of epi-brassinolide and brassinazole, an inhibitor of BR biosynthesis. We show that the phenotype of the transgenic tobacco plants with increased or reduced MSBP1 expression is consistent with an inhibitory role of MSBP1 in BR signaling. MSBP1 overexpression could be mimicked by brassinazole treatment. Interestingly, manipulation of MSBP1 expression in transgenic tobacco plants not only affected plant growth and development, but also the host plant responses toward colonization with AM fungi, as well as arbuscular architecture. Moreover, we observed that brassinosteroids indeed have a direct impact on the nutrient exchange in AM symbiosis and on the biomass production of colonized host plants. Furthermore, arbuscular morphology is affected by changes in MSBP1 expression and brassinolide or brassinazole treatments. We conclude that host plant growth responses and nutrient exchange within the symbiosis with AM fungi is controlled by brassinosteroids and might be impeded by the MSBP1 protein

Proceedings in Marine Biology

Journal of the Graduate Course of the Freie Universiät Berlin (Germany) at Kristinebergs Marina Forskningsstation (Sweden)Zeitschrift zur Kursreise der Freien Universität Berlin (Deutschland) an die Kristinebergs Marina Forskningsstation (Schweden)Peer Reviewe

How chronobiology can affect local population dynamics and spatial distribution in Antarctic Krill

We investigate how individual growth and population structure of Antarctic krill (Euphausia superba) would be affected by changes in the spatio-temporal dynamics of the sea ice cover. This is of high interest since krill has adapted to a particular environmental regime which is likely to change dramatically over the coming years. The response of krill will in particular depend on its chronobiology: when and why does krill, after a period of decreased metabolic activity during winter, switch back to an active metabolic state? If this switch is purely triggered by the Zeitgeber day length, the metabolically active period of krill and the availability of food resources would become out of phase with potentially drastic consequences for krill populations. Alternatively, the switch might also be triggered by food availability. To explore the consequences of different environmental scenarios and assumptions about krill chronobiology, we developed a spatially explicit individual-based simulation model. The model operates on a daily time step. Each time step ice cover extent and day length for each grid cell in the model are updated. In the model demographic and behavioural processes are simulated every time step. Particularly all modelled krill individuals grow depending on food availability, move, reproduce given their reproductive and metabolic state, and die with a certain probability. Growth and reproduction are modelled according to a simplified version of dynamic energy budget theory (DEBKiss). Simulations run for several years until quasi-stationary population characteristics have emerged. Population metrics such as length distribution and heterogeneity in reproductive state within the population are observed. We will present the model and demonstrate its potential by contrasting results for selected environmental and chronobiological scenarios. The model’s design and implementation are open so that suggestions regarding alternative assumptions and scenarios can easily be implemented and explored

How biological clocks and changing environmental conditionsdetermine local population growth and species distribution inAntarctic krill (Euphausia superba): a conceptual model

The Southern Ocean ecosystem is characterized by extreme seasonal changes in environmental factors such as day length, sea ice extent and food availability. The key species Antarctic krill (Euphausia superba) has evolved metabolic and behavioural seasonal rhythms to cope with these seasonal changes. We investigate the switch between a physiological less active and active period for adult krill, a rhythm which seems to be controlled by internal biological clocks. These biological clocks can be synchronized by environmental triggers such as day length and food availability. They have evolved for particular environmental regimes to synchronize predictable seasonal environmental changes with important life cycle functions of the species. In a changing environment the time when krill is metabolically active and the time of peak food availability may not overlap if krill's seasonal activity is solely determined by photoperiod (day length). This is especially true for the Atlantic sector of the Southern Ocean where the spatio-temporal ice cover dynamics are changing substantially with rising average temperatures. We developed an individual-based model for krill to explore the impact of photoperiod and food availability on the growth and demographics of krill. We simulated dynamics of local krill populations (with no movement of krill assumed) along a south-north gradient for different triggers of metabolic activity and different levels of food availability below the ice. We also observed the fate of larval krill which cannot switch to low metabolism and therefore are likely to overwinter under ice. Krill could only occupy the southern end of the gradient, where algae bloom only lasts for a short time, when alternative food supply under the ice was high and metabolic activity was triggered by photoperiod. The northern distribution was limited by lack of overwintering habitat for krill larvae due to short duration of sea ice cover even for high food content under the ice. The variability of the krill's length-frequency distributions varied for different triggers of metabolic activity, but did not depend on the sea ice extent. Our findings suggest a southward shift of krill populations due to reduction in the spatial sea ice extent, which is consistent with field observations. Overall, our results highlight the importance of the explicit consideration of spatio-temporal sea ice dynamics especially for larval krill together with temporal synchronization through internal clocks, triggered by environmental factors (photoperiod and food) in adult krill for the population modelling of krill