Antimicrobial peptide expression in a wild tobacco plant reveals the limits of host-microbe-manipulations in the field

Plant-microbe associations are thought to be beneficial for plant growth and resistance against biotic or abiotic stresses, but for natural ecosystems, the ecological analysis of microbiome function remains in its infancy. We used transformed wild tobacco plants (Nicotiana attenuata) which constitutively express an antimicrobial peptide (Mc-AMP1) of the common ice plant, to establish an ecological tool for plant-microbe studies in the field. Transgenic plants showed in planta activity against plant-beneficial bacteria and were phenotyped within the plants´ natural habitat regarding growth, fitness and the resistance against herbivores. Multiple field experiments, conducted over 3 years, indicated no differences compared to isogenic controls. Pyrosequencing analysis of the root-associated microbial communities showed no major alterations but marginal effects at the genus level. Experimental infiltrations revealed a high heterogeneity in peptide tolerance among native isolates and suggests that the diversity of natural microbial communities can be a major obstacle for microbiome manipulations in nature

Transcriptome profiling reveals differential gene expression of detoxification enzymes in a hemimetabolous tobacco pest after feeding on jasmonate-silenced Nicotiana attenuata plants

Putatively unique transcripts (PUTs) used in real-time qPCR (RT-qPCR) expression analysis. (XLSX 12 kb

On the survivability and detectability of terrestrial meteorites on the moon

Materials blasted into space from the surface of early Earth may preserve a unique record of our planet's early surface environment. Armstrong et al. (2002) pointed out that such materials, in the form of terrestrial meteorites, may exist on the Moon and be of considerable astrobiological interest if biomarkers from early Earth are preserved within them. Here, we report results obtained via the AUTODYN hydrocode to calculate the peak pressures within terrestrial meteorites on the lunar surface to assess their likelihood of surviving the impact. Our results confirm the order-of-magnitude estimates of Armstrong et al. (2002) that substantial survivability is to be expected, especially in the case of relatively low velocity (ca. 2.5 km/s) or oblique (≤45°) impacts, or both. We outline possible mechanisms for locating such materials on the Moon and conclude that searching for them would be a scientifically valuable activity for future lunar exploration

Two-way communication between SecY and SecA suggests a Brownian ratchet mechanism for protein translocation

The essential process of protein secretion is achieved by the ubiquitous Sec machinery. In prokaryotes, the drive for translocation comes from ATP hydrolysis by the cytosolic motor- protein SecA, in concert with the proton motive force (PMF). However, the mechanism through which ATP hydrolysis by SecA is coupled to directional movement through SecYEG is unclear. Here, we combine all-atom molecular dynamics (MD) simulations with single molecule FRET and biochemical assays. We show that ATP binding by SecA causes opening of the SecY- channel at long range, while substrates at the SecY-channel entrance feed back to regulate nucleotide exchange by SecA. This two-way communication suggests a new, unifying 'Brownian ratchet' mechanism, whereby ATP binding and hydrolysis bias the direction of polypeptide diffusion. The model represents a solution to the problem of transporting inherently variable substrates such as polypeptides, and may underlie mechanisms of other motors that translocate proteins and nucleic acids

Equitability revisited: why the “equitable threat score” is not equitable

In the forecasting of binary events, verification measures that are “equitable” were defined by Gandin and Murphy to satisfy two requirements: 1) they award all random forecasting systems, including those that always issue the same forecast, the same expected score (typically zero), and 2) they are expressible as the linear weighted sum of the elements of the contingency table, where the weights are independent of the entries in the table, apart from the base rate. The authors demonstrate that the widely used “equitable threat score” (ETS), as well as numerous others, satisfies neither of these requirements and only satisfies the first requirement in the limit of an infinite sample size. Such measures are referred to as “asymptotically equitable.” In the case of ETS, the expected score of a random forecasting system is always positive and only falls below 0.01 when the number of samples is greater than around 30. Two other asymptotically equitable measures are the odds ratio skill score and the symmetric extreme dependency score, which are more strongly inequitable than ETS, particularly for rare events; for example, when the base rate is 2% and the sample size is 1000, random but unbiased forecasting systems yield an expected score of around −0.5, reducing in magnitude to −0.01 or smaller only for sample sizes exceeding 25 000. This presents a problem since these nonlinear measures have other desirable properties, in particular being reliable indicators of skill for rare events (provided that the sample size is large enough). A potential way to reconcile these properties with equitability is to recognize that Gandin and Murphy’s two requirements are independent, and the second can be safely discarded without losing the key advantages of equitability that are embodied in the first. This enables inequitable and asymptotically equitable measures to be scaled to make them equitable, while retaining their nonlinearity and other properties such as being reliable indicators of skill for rare events. It also opens up the possibility of designing new equitable verification measures

Host-plant-mediated effects of Nadefensin on herbivore and pathogen resistance in Nicotiana attenuata

<p>Abstract</p> <p>Background</p> <p>The adage from Shakespeare, "troubles, not as single spies, but in battalions come," holds true for <it>Nicotiana attenuata</it>, which is commonly attacked by both pathogens (<it>Pseudomonas spp</it>.) and herbivores (<it>Manduca sexta</it>) in its native habitats. Defense responses targeted against the pathogens can directly or indirectly influence the responses against the herbivores. Na<it>defensin </it>is an effective induced defense gene against the bacterial pathogen <it>Pseudomonas syringae </it>pv <it>tomato </it>(PST DC3000), which is also elicited by attack from <it>M. sexta </it>larvae, but whether this defense protein influences <it>M. sexta's </it>growth and whether <it>M. sexta</it>-induced Na<it>defensin </it>directly or indirectly influences PST DC3000 resistance are unknown.</p> <p>Results</p> <p><it>M. sexta </it>larvae consumed less on WT and on Na<it>defensin</it>-silenced <it>N. attenuata </it>plants that had previously been infected with PST DC3000 than on uninfected plants. WT plants infected with PST DC3000 showed enhanced resistance to PST DC3000 and decreased leaf consumption by <it>M. sexta </it>larvae, but larval mass gain was unaffected. PST DC3000-infected Na<it>defensin</it>-silenced plants were less resistant to subsequent PST DC3000 challenge, and on these plants, <it>M. sexta </it>larvae consumed less and gained less mass. WT and Na<it>defensin</it>-silenced plants previously damaged by <it>M. sexta </it>larvae were better able to resist subsequent PST DC3000 challenges than were undamaged plants.</p> <p>Conclusion</p> <p>These results demonstrate that Na-defensin directly mediates defense against PST DC3000 and indirectly against <it>M. sexta </it>in <it>N. attenuata</it>. In plants that were previously infected with PST DC3000, the altered leaf chemistry in PST DC3000-resistant WT plants and PST DC3000-susceptible Na<it>defensin</it>-silenced plants differentially reduced <it>M. sexta's </it>leaf consumption and mass gain. In plants that were previously damaged by <it>M. sexta</it>, the combined effect of the altered host plant chemistry and a broad spectrum of anti-herbivore induced metabolomic responses was more effective than Na<it>defensin </it>alone in resisting PST DC3000.</p

Spitzer reveals what's behind Orion's Bar

We present Spitzer Space Telescope observations of 11 regions SE of the Bright Bar in the Orion Nebula, along a radial from the exciting star theta1OriC, extending from 2.6 to 12.1'. Our Cycle 5 programme obtained deep spectra with matching IRS short-high (SH) and long-high (LH) aperture grid patterns. Most previous IR missions observed only the inner few arcmin. Orion is the benchmark for studies of the ISM particularly for elemental abundances. Spitzer observations provide a unique perspective on the Ne and S abundances by virtue of observing the dominant ionization states of Ne (Ne+, Ne++) and S (S++, S3+) in Orion and H II regions in general. The Ne/H abundance ratio is especially well determined, with a value of (1.01+/-0.08)E-4. We obtained corresponding new ground-based spectra at CTIO. These optical data are used to estimate the electron temperature, electron density, optical extinction, and the S+/S++ ratio at each of our Spitzer positions. That permits an adjustment for the total gas-phase S abundance because no S+ line is observed by Spitzer. The gas-phase S/H abundance ratio is (7.68+/-0.30)E-6. The Ne/S abundance ratio may be determined even when the weaker hydrogen line, H(7-6) here, is not measured. The mean value, adjusted for the optical S+/S++ ratio, is Ne/S = 13.0+/-0.6. We derive the electron density versus distance from theta1OriC for [S III] and [S II]. Both distributions are for the most part decreasing with increasing distance. A dramatic find is the presence of high-ionization Ne++ all the way to the outer optical boundary ~12' from theta1OriC. This IR result is robust, whereas the optical evidence from observations of high-ionization species (e.g. O++) at the outer optical boundary suffers uncertainty because of scattering of emission from the much brighter inner Huygens Region.Comment: 60 pages, 16 figures, 10 tables. MNRAS accepte

Opportunistic out-crossing in Nicotiana attenuata (Solanaceae), a predominantly self-fertilizing native tobacco

BACKGROUND: Although Nicotiana attenuata is entirely self-compatible, chemical and other floral traits suggest selection for the maintenance of advertisement for moth pollinators. RESULTS: Experimental exclusions of pollinators from plants with emasculated flowers in natural populations in southern Utah during an outbreak of the hawkmoth Hyles lineata revealed that 24% of the seed set could be attributed to insect pollination, and eliminated wind pollination and apomixis as contributing to seed set. Hence these moths can mediate gene flow when self-pollen is unavailable. To quantify gene flow when self-pollen is available, plants were transformed with two marker genes: hygromycin-B resistance and β-glucuronidase. The utility of these genetic markers to measure gene flow between plants was examined by mixing pollen from plants homozygous for both genes with self-pollen in different ratios and hand-pollinating emasculated flowers of plants growing in a natural population. The proportion of transformed seeds was positively correlated with the amount of transformed pollen applied to stigmas. In glasshouse experiments with the hawkmoth Manduca sexta and experimental arrays of transformed and wild-type plants, pollination mediated by moths accounted for 2.5% of the seed set. CONCLUSIONS: Even though moth pollination is rare and highly variable for this largely selfing plant, N. attenuata opportunistically employs a mixed-mating system