Specificity of Collybistin-Phosphoinositide Interactions: IMPACT OF THE INDIVIDUAL PROTEIN DOMAINS*

The regulatory protein collybistin (CB) recruits the receptor-scaffolding protein gephyrin to mammalian inhibitory glycinergic and GABAergic postsynaptic membranes in nerve cells. CB is tethered to the membrane via phosphoinositides. We developed an in vitro assay based on solid-supported 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membranes doped with different phosphoinositides on silicon/silicon dioxide substrates to quantify the binding of various CB2 constructs using reflectometric interference spectroscopy. Based on adsorption isotherms, we obtained dissociation constants and binding capacities of the membranes. Our results show that full-length CB2 harboring the N-terminal Src homology 3 (SH3) domain (CB2_SH3+) adopts a closed and autoinhibited conformation that largely prevents membrane binding. This autoinhibition is relieved upon introduction of the W24A/E262A mutation, which conformationally “opens” CB2_SH3+ and allows the pleckstrin homology domain to properly bind lipids depending on the phosphoinositide species with a preference for phosphatidylinositol 3-monophosphate and phosphatidylinositol 4-monophosphate. This type of membrane tethering under the control of the release of the SH3 domain of CB is essential for regulating gephyrin clustering.     

Ethylene and IAA interactions in the inhibition of photoperiodic flower induction of <Emphasis Type="Italic">Pharbitis nil</Emphasis>

It has been shown that both IAA and ethylene application inhibit flower induction in the short-day plant Pharbitis nil. However application of IAA has elevated ethylene production in this plant, as well. Strong enhancement of ethylene production is also correlated with the night-break effect, which completely inhibits flowering. In order to determine what the role of IAA and ethylene is in the photoperiodic flower induction in Pharbitis nil, we measured changes in their levels during inductive and non-inductive photoperiods, and the effects of ethylene biosynthesis and action inhibitors on inhibition of flowering by IAA. Our results have shown that the inhibitory effect of IAA on Pharbitis nil flowering is not physiological but is connected with its effect on ethylene biosynthesis.     

What shapes giant hogweed invasion? Answers from a spatio-temporal model integrating multiscale monitoring data

In this study we simulated the invasion of Heracleum mantegazzianum with a spatiotemporal model that combined a life-cycle matrix model with mechanistic local and corridor dispersal and a stochastic long-distance dispersal in a cellular automaton. The model was applied to the habitat configuration and invader distribution of eight 1?km2 study areas. Comparing the simulations with monitoring data collected over 7?years (2002?C2009) yielded a modelling efficiency of 0.94. We tested the significance of different mechanisms of invasion by omitting or modifying single model components one at a time. Thus we found that the extent of H. mantegazzianum invasion at landscape level depends on both landscape-scale processes and local processes which control recruitment success and population density. Limiting recruitment success (100????30?%) and successionally decreasing the carrying capacity of habitats (max????0) over 30?years significantly improved the projections of the invasion at the landscape level. Local dispersal reached farther than 10?m, i.e. farther than previously assumed, but appeared to be unaffected by wind directions. Long-distance dispersal together with local dispersal dominated the invasion quantitatively. Dispersal through corridors accounted for less invasive spread. Its importance, with respect to invasion speed (number of colonised model grid cells) is probably limited over short periods of time (7?years). Only dispersal along rivers made a significant quantitative contribution to invasion of H. mantegazzianum. We suggest that biotic heterogeneity of suitable habitats is responsible for varying invasion success and that successionally increasing competition leads to declining population densities of H. mantegazzianum over several decades slowing down the spread on the landscape scale.