Friend or foe? A parasitic wasp shifts the cost/benefit ratio in a nursery pollination system impacting plant fitness

Nursery pollination systems are species interactions where pollinators also act as fruit/seed herbivores of the plant partner. While the plants depend on associated insects for pollination, the insects depend on the plants’ reproductive structures for larval development. The outcome of these interactions is thus placed on a gradient between mutualism and antagonism. Less specialized interactions may fluctuate along this gradient with the ecological context, where natural enemies can play an important role. We studied whether a natural enemy may impact the level of seed consumption of a nursery pollinator and how this in turn may influence individual plant fitness. We used the plant Silene latifolia, its herbivore Hadena bicruris, and its ectoparasitoid Bracon variator as a model plant–herbivore–natural enemy system. We investigated seed output, germination, survival, and flower production as proxies for individual plant fitness. We show that B. variator decreases the level of seed consumption by H. bicruris larvae which in turn increased seed output in S. latifolia plants, suggesting that parasitism by B. variator may act as a regulator in the system. However, our results also show that plant survival and flower production decrease with higher seed densities, and therefore, an increase in seed output may be less beneficial for plant fitness than estimated from seed output alone. Our study should add another layer to the complex discussion of whether parasitoids contribute to plant fitness, as we show that taking simple proxies such as seed output is insufficient to determine the net effect of multitrophic interactions.     

Looping in on Ndc80 – How does a protein loop at the kinetochore control chromosome segregation?

Segregation of chromosomes during mitosis requires the interaction of dynamic microtubules with the kinetochore, a large protein structure established on the centromere region of sister chromatids. The core microtubule‐binding activity of the kinetochore resides in the KMN network, an outer kinetochore complex. As part of the KMN network, the Ndc80 complex, which is composed of Ndc80, Nuf2, Spc24, and Spc25, is able to bind directly to microtubules and has the ability to track with depolymerizing microtubules to produce chromosome movement. The Ndc80 complex binds directly to microtubules through a calponin homology domain and an unstructured tail in the N terminus of the Ndc80 protein. A recent flurry of papers has highlighted the importance of an internal loop region in Ndc80 in establishing end‐on attachment to microtubules. Here I discuss these recent findings that suggest that the Ndc80 internal loop functions as a binding site for proteins required for kinetochore‐microtubule interactions.     

Electron transfer from the Rieske iron-sulfur protein (ISP) to cytochrome f in vitro. Is a guided trajectory of the ISP necessary for competent docking?

The time course of electron transfer in vitro between soluble domains of the Rieske iron-sulfur protein (ISP) and cytochrome f subunits of the cytochrome b(6)f complex of oxygenic photosynthesis was measured by stopped-flow mixing. The domains were derived from Chlamydomonas reinhardtii and expressed in Escherichia coli. The expressed 142-residue soluble ISP apoprotein was reconstituted with the [2Fe-2S] cluster. The second-order rate constant, k(2)((ISP-f)) = 1.5 x 10(6) m(-1) s(-1), for ISP to cytochrome f electron transfer was <10(-2) of the rate constant at low ionic strength, k(2)((f-PC))(> 200 x 10(6) m(-1) s(-1)), for the reduction of plastocyanin by cytochrome f, and approximately 1/30 of k(2)((f-PC)) at the ionic strength estimated for the thylakoid interior. In contrast to k(2)((f-PC)), k(2)((ISP-f)) was independent of pH and ionic strength, implying no significant role of electrostatic interactions. Effective pK values of 6.2 and 8.3, respectively, of oxidized and reduced ISP were derived from the pH dependence of the amplitude of cytochrome f reduction. The first-order rate constant, k(1)((ISP-f)), predicted from k(2)((ISP-f)) is approximately 10 and approximately 150 times smaller than the millisecond and microsecond phases of cytochrome f reduction observed in vivo. It is proposed that in the absence of electrostatic guidance, a productive docking geometry for fast electron transfer is imposed by the guided trajectory of the ISP extrinsic domain. The requirement of a specific electrically neutral docking configuration for ISP electron transfer is consistent with structure data for the related cytochrome bc(1) complex.     

In vitro and in vivo antitumor activity of a mouse CTL hybridoma expressing chimeric receptors bearing the single chain Fv from HER-2/neu- specific antibody and the γ-chain from Fc(ε) RI

To broaden the applicability of adoptive cellular immunotherapy against HER-2/neu overexpressing human cancers, we constructed a chimeric scFv/gamma gene composed of the variable regions of a HER-2/neu specific monoclonal antibody (mAb) joined to the signaling gamma-chain of the Fc(epsilon)RI receptor. The scFv(anti-HER-2/neu)/gamma chimeric gene was successfully expressed as functional surface receptor in the MD.45 cytolytic T-cell (CTL) hybridoma (MD.45-HER/gamma). Expression of the chimeric protein triggered IL-2 and IFN-gamma secretion in vitro upon encountering cell surface HER-2/neu and mediated non-major-histocompatibility-complex (MHC)-restricted HER-2/neu-specific target cell lysis. We also examined the in vivo activity of the MD.45-HER/gamma transduced cells. Severe combined immunodeficiency disease (SCID) mice that were given HER-2/neu positive (+) human tumor cell lines had significantly increased survival compared to mice treated with saline only, or with MD.45 cells transduced with a control anti-trinitrophenyl (anti-TNP) chimeric receptor gene (MD.45-TNP/gamma). These results demonstrate the feasibility of redirecting MD.45 CTL to react in vitro and in vivo with a variety of HER-2/neu(+) tumor cells by our gene transduction protocol. Moreover, they open the possibility of using the same chimeric gene for transducing primary lymphocytes and thus allowing adoptive immunotherapy against HER-2/neu(+) cancers.     

Lysophosphatidic acid signals through mitogen-activated protein kinase-extracellular signal regulated kinase in ovarian theca cells expressing the LPA1/edg2-receptor: involvement of a nonclassical pathway?

We investigated the mechanism of lysophosphatidic acid (LPA) signaling in ovarian theca cells and observed that stimulation with this bioactive lipid markedly enhanced Thr/Tyr phosphorylation of the MAPK ERK1/2. Activation of ERK was transient, showing a peak at 5 min that declined thereafter, and was not associated with a concomitant nuclear translocation of the enzyme, suggesting that a cytosolic tyrosine phosphatase may be responsible for switching off the signal. Epidermal growth factor (EGF)-induced activation of the enzyme in the same cell system was more rapid (peaking at 1 min), sustainable for at least 60 min, and could be suppressed by prior treatment with either pertussis toxin or a noncompetitive inhibitor of Ras acceptor protein, manumycin A. This functional inhibition of either Gi or Ras failed, however, to affect the LPA-induced ERK-phosphorylation. Surprisingly, functional inhibition of Rho-GTPase, in C3-exotoxin-lipofected cells, markedly reduced LPA-stimulated phosphorylation of ERK, without affecting the EGF-induced stimulation of MAPK. Theca cells labeled with anti-LPA1/edg2-type antibody showed a distinct cell surface labeling, which is reflected in the expression of (LPA1)-type LPA receptors at both mRNA and protein levels. The findings indicate that LPA transiently stimulates MAPK ERK in LPA1/edg2-expressing theca cells and suggest an alternative mechanism regulating the activation of ERK that differs from the canonical EGF-Ras-MAPK kinase pathway.     

The proline-rich region of 18.5 kDa myelin basic protein binds to the SH3-domain of Fyn tyrosine kinase with the aid of an upstream segment to form a dynamic complex in?vitro

The intrinsically disordered 18.5 kDa classic isoform of MBP (myelin basic protein) interacts with Fyn kinase during oligodendrocyte development and myelination. It does so primarily via a central proline-rich SH3 (Src homology 3) ligand (T92–R104, murine 18.5 kDa MBP sequence numbering) that is part of a molecular switch due to its high degree of conservation and modification by MAP (mitogen-activated protein) and other kinases, especially at residues T92 and T95. Here, we show using co-transfection experiments of an early developmental oligodendroglial cell line (N19) that an MBP segment upstream of the primary ligand is involved in MBP–Fyn–SH3 association in cellula. Using solution NMR spectroscopy in vitro, we define this segment to comprise MBP residues (T62–L68), and demonstrate further that residues (V83–P93) are the predominant SH3-target, assessed by the degree of chemical shift change upon titration. We show by chemical shift index analysis that there is no formation of local poly-proline type II structure in the proline-rich segment upon binding, and by NOE (nuclear Overhauser effect) and relaxation measurements that MBP remains dynamic even while complexed with Fyn–SH3. The association is a new example first of a non-canonical SH3-domain interaction and second of a fuzzy MBP complex.     

Managing invasions at the cost of native habitat? An experimental test of the impact of fire on the invasion of <Emphasis Type="Italic">Chromolaena odorata</Emphasis> in a South African savanna

Successfully managing invasive plants in natural systems is extremely difficult. Recently however, progress has been made with an approach focused on changing ecosystem processes through the disturbance regime. We performed a large-scale (3 ha) full-factorial field experiment in densely invaded woodland in Hluhluwe-iMfolozi Park, a savanna reserve in South Africa, to study the effect of fire on the control of the pan-tropical invasive exotic shrub Chromolaena odorata in combination with the conventional method, i.e. manual clearing and herbicide application. We show how fire interacted with the conventional clearing of C. odorata and induced an intense canopy fire that caused a shift from woodland to grassland. After 2.5 years of monitoring, grasses were still dominant and re-invasion minimal. It is important to note that fire without prior clearing did not have the same effect and was not successful in reducing densities of C. odorata. An integrated control practice targeting the species with mechanical and chemical methods, while simultaneously targeting its habitat through fire, effectively controlled dense C. odorata thickets during the course of the experiment. However, this approach transformed regular surface fires into high-intensity canopy fires that are rare in savannas. We discuss how this altered fire regime may threaten native habitats, including fire-sensitive forest patches and riverine woodlands within the savanna mozaic. This is an important dilemma for managers that should not be overlooked and asks for long-term data on the impact of control programs on the native vegetation.     

Effect of monomeric and oligomeric sugar osmolytes on ΔGD, the Gibbs energy of stabilization of the protein at different pH values: Is the sum effect of monosaccharide individually additive in a mixture?

Thermal denaturation curves of ribonuclease-A were measured by monitoring changes in the far-UV circular dichroism (CD) spectra in the presence of different concentrations of six sugars (glucose, fructose, galactose, sucrose, raffinose and stachyose) and mixture of monosaccharide constituents of each oligosaccharide at various pH values in the range of 6.0-2.0. These measurements gave values of T(m) (midpoint of denaturation), DeltaH(m) (enthalpy change at T(m)), DeltaC(p) (constant-pressure heat capacity change) under a given solvent condition. Using these values of DeltaH(m), T(m) and DeltaC(p) in appropriate thermodynamic relations, thermodynamic parameters at 25 degrees C, namely, DeltaG(D)(o) (Gibbs energy change), DeltaH(D)(o) (enthalpy change), and DeltaS(D)(o) (entropy change) were determined at a given pH and concentration of each sugar (including its mixture of monosaccharide constituents). Our main conclusions are: (i) each sugar stabilizes the protein in terms of T(m) and DeltaG(D)(o), and this stabilization is under enthalpic control, (ii) the protein stabilization by the oligosaccharide is significantly less than that by the equimolar concentration of the constituent monosaccharides, and (iii) the stabilization by monosaccharides in a mixture is fully additive. Furthermore, measurements of the far- and near-UV CD spectra suggested that secondary and tertiary structures of protein in their native and denatured states are not perturbed on the addition of sugars.