Quantifying the outcome of plant–granivore interactions

In many interspecific interactions, the balance of costs and benefits varies with ecological circumstances. As a prominent example, seed‐caching granivores may act as seed predators and reduce plant recruitment or as seed dispersers and increase recruitment, making it difficult to interpret whether differences in seed removal by granivores would harm or benefit plant populations. We used a heuristic model to evaluate the outcome of plant‐granivore interactions, using commonly measured field data: probability of seedling emergence when granivores are excluded, and emergence of cached and uneaten seeds. Published studies to date suggest that the outcome of plant‐rodent interactions tends weakly towards mutualism, but differs among particular plant–granivore pairs and ecological conditions, supporting the notion of context‐dependence. A modeling framework also allowed us to distinguish parameters that affect the qualitative outcome of plant–granivore interactions from those that do not. Similar approaches would facilitate more efficient and cost‐effective evaluation of complex species interactions.     

The population ecology of novel plant–herbivore interactions

Many native herbivores are known to attack exotic plants, and we can expect these interactions to occur with increasing frequency in coming years as invasive plants become naturalized and new invaders arrive in native communities. In some cases, evolutionary biologists and ecologists have learned a great deal from insects adapting to novel hosts. However, there is more to be learned and we suggest that the ecological study of exotic host colonization by native insects has been impeded by a lack of focus in the questions being asked, and also from overlap with other areas of plant–insect ecology, including the study of specialization. In the present paper, a conceptual model is described for the colonization of a novel host‐plant, which focuses on the relationship between occupancy and availability. Occupancy is the fraction of patches of novel hosts that are utilized by an herbivore, and availability is the abundance or presence of a novel host on the landscape. Considering the slope of that relationship (between occupancy and availability), hypotheses are suggested that involve dispersal and, most important, population growth rate of an insect herbivore associated with an exotic host. A focus on the occupancy–availability relationship highlights the strengths and weaknesses of common experimental approaches, such as preference–performance experiments. Suggestions for future work are offered that include integration with evolutionary theory and exploration of more complex demographic and ecological scenarios.     

Disturbance influences the outcome of plant–soil biota interactions in the invasive Acacia longifolia and in native species

Interrelated causes of plant invasion have been gaining increasing recognition. However, research on this subject has mainly focused around conceptual models. Here we explore whether plant–soil biota feedbacks and disturbance, two major factors capable of facilitating invasive plants in introduced ranges, interact to preferentially benefit exotics compared to native plants. We investigated the influence of fire disturbance on plant–soil biota interactions for the invasive Acacia longifolia and two dominant natives (Cytisus striatus and Pinus pinaster) in Portuguese dune systems. In the first experiment, we grew exotic and native plants in soil inoculated with soil biota from unburned or recently burned soils collected in an area with small invasion intensity by A. longifolia. Soil biota effects on the exotic legume A. longifolia changed from neutral to positive after fire, whereas the opposite outcome was observed in the native legume C. striatus, and a change from negative to neutral effects after fire occurred in the native P. pinaster. Fire reduced mycorrhizal colonization in all species and rhizobial colonization in C. striatus but not in A. longifolia. In the second experiment, we grew the exotic and native plants with conspecific and heterospecific soil biota from undisturbed soils (area with low invasion intensity by A. longifolia), and from post‐fire soils (area affected by a fire ～12 years ago and currently heavily invaded by A. longifolia). The exotic benefited more from post‐fire than from undisturbed soil biota, particularly from those associated with natives. Natives did not experience detrimental effects with invasive‐associated soil biota. Our results show that fire disturbance affected the functional interactions between soil biota and plants that may benefit more the exotic than some native species. Disturbance may open a window of opportunity that promotes invader success by altering soil enemy and mutualistic impacts.     

In shallow water ecosytems the abiotic environment is more important than prey abundance for foraging terns

Shallow freshwater aquatic ecosystems are discrete feeding patches for fish eating birds. A unique feature of these ecosystems is that their physical conditions can change dramatically in a short period of time, particularly temperature, turbidity, and dissolved oxygen. Based on previous research we predicted that increasing turbidity will reduce the availability of fish to birds due to reduced visibility, while increasing temperature and decreasing dissolved oxygen will increase their availability through increases in activity and movement towards the more oxygenated surface areas, respectively. We also predicted that overall abundance of fish should increase feeding activity by terns. We measured these environmental variables, bird activity, and fish abundance from May to August from 2006 to 2008 in a marsh in southern Manitoba, Canada. Our results showed that only variation in dissolved oxygen levels affected feeding activity by terns. Since there was no relationship between bird and fish abundance either within or among years, these results suggest that it is the availability of prey (i.e. the upward movement of fish into the water column) and not their abundance per se that influences the number of avian predators present and hence the risk of predation to fish. These data demonstrate how the physical environment of aquatic ecosystems can impact terrestrial avian predators, and the link that exists between the physical environment and predator-prey interactions.     

SGT1 positively regulates the process of plant cell death during both compatible and incompatible plant–pathogen interactions

SGT1 (suppressor of G2 allele of Skp1), an interactor of SCF (Skp1‐Cullin‐F‐box) ubiquitin ligase complexes that mediate protein degradation, plays an important role at both G1–S and G2–M cell cycle transitions in yeast, and is highly conserved throughout eukaryotes. Plant SGT1 is required for both resistance (R) gene‐mediated disease resistance and nonhost resistance to certain pathogens. Using virus‐induced gene silencing (VIGS) in Nicotiana benthamiana, we demonstrate that SGT1 positively regulates the process of cell death during both host and nonhost interactions with various pathovars of Pseudomonas syringae. Silencing of NbSGT1 in N. benthamiana plants delays the induction of hypersensitive response (HR)‐mediated cell death against nonhost pathogens and the development of disease‐associated cell death caused by the host pathogen P. syringae pv. tabaci. Our results further demonstrate that NbSGT1 is required for Erwinia carotovora‐ and Sclerotinia sclerotiorum‐induced disease‐associated cell death. Overexpression of NbSGT1 in N. benthamiana accelerates the development of HR during R gene‐mediated disease resistance and nonhost resistance. Our data also indicate that SGT1 is required for pathogen‐induced cell death, but is not always necessary for the restriction of bacterial multiplication in planta. Therefore, we conclude that SGT1 is an essential component affecting the process of cell death during both compatible and incompatible plant–pathogen interactions.     

Landscape structure,dispersal and the evolution of antagonistic plant–herbivore interactions

Different species have different dispersal capabilities and in the field, species interact with each other within dynamic, heterogeneous and complex landscapes. While plants and certain herbivore species may disperse considerable distances by means of seed dispersal or flight, other herbivores (e.g. root‐feeding nematodes or non‐winged insect herbivores) are more limited in their dispersal capacities. This difference in dispersal capabilities results in mosaics of plant–herbivore interactions that shift over time and space leading to spatio‐temporal variation in both the presence and absence of the species and their interactions. We developed an individual based simulation model in which we examined how multi‐species interactions are affected by their mobility within structurally complex landscapes. The main objective was to address the consequences for the arms race between plant defence and herbivore resistance to changes in fundamental landscape and community attributes. We demonstrate that feedbacks between landscape structure, community structure and the specific dispersal rate of the species involved affect the evolutionary dynamics between plants and herbivore antagonists. While three‐species interactions result in increased plant defence and herbivore resistance, effects of dispersal have diverse effects depending on the prevailing landscape structure.     

Subcellular targeting of an evolutionarily conserved plant defensin MtDef4.2 determines the outcome of plant–pathogen interaction in transgenic Arabidopsis

The Medicago truncatula gene encoding an evolutionarily conserved antifungal defensin MtDef4.2 was cloned and characterized. In silico expression analysis indicated that MtDef4.2 is expressed in many tissues during the normal growth and development of M. truncatula. MtDef4.2 exhibits potent broad‐spectrum antifungal activity against various Fusarium spp. Transgenic Arabidopsis thaliana lines in which MtDef4.2 was targeted to three different subcellular compartments were generated. These lines were tested for resistance to the obligate biotrophic oomycete Hyaloperonospora arabidopsidis Noco2 and the hemibiotrophic fungal pathogen Fusarium graminearum PH‐1. MtDef4.2 directed to the extracellular space, but not to the vacuole or retained in the endoplasmic reticulum, conferred robust resistance to H. arabidopsidis. Siliques of transgenic Arabidopsis lines expressing either extracellularly or intracellularly targeted MtDef4.2 displayed low levels of resistance to F. graminearum, but accumulated substantially reduced levels of the mycotoxin deoxynivalenol. The data presented here suggest that extracellularly targeted MtDef4.2 is sufficient to provide strong resistance to the biotrophic oomycete, consistent with the extracellular lifestyle of this pathogen. However, the co‐expression of extracellular and intracellular MtDef4.2 is probably required to achieve strong resistance to the hemibiotrophic pathogen F. graminearum which grows extracellularly and intracellularly.     

Grazing‐induced changes in plant–soil feedback alter plant biomass allocation

Large vertebrate herbivores, as well as plant–soil feedback interactions are important drivers of plant performance, plant community composition and vegetation dynamics in terrestrial ecosystems. However, it is poorly understood whether and how large vertebrate herbivores and plant–soil feedback effects interact. Here, we study the response of grassland plant species to grazing‐induced legacy effects in the soil and we explore whether these plant responses can help us to understand long‐term vegetation dynamics in the field. In a greenhouse experiment we tested the response of four grassland plant species, Agrostis capillaris, Festuca rubra, Holcus lanatus and Rumex acetosa, to field‐conditioned soils from grazed and ungrazed grassland. We relate these responses to long‐term vegetation data from a grassland exclosure experiment in the field. In the greenhouse experiment, we found that total biomass production and biomass allocation to roots was higher in soils from grazed than from ungrazed plots. There were only few relationships between plant production in the greenhouse and the abundance of conspecifics in the field. Spatiotemporal patterns in plant community composition were more stable in grazed than ungrazed grassland plots, but were not related to plant–soil feedbacks effects and biomass allocation patterns. We conclude that grazing‐induced soil legacy effects mainly influenced plant biomass allocation patterns, but could not explain altered vegetation dynamics in grazed grasslands. Consequently, the direct effects of grazing on plant community composition (e.g. through modifying light competition or differences in grazing tolerance) appear to overrule indirect effects through changes in plant–soil feedback.     

Plant–plant interactions and soil moisture might be important in determining ozone impacts on grasslands

Ozone effects on plant species mixtures could depend on the characteristics of the species involved, their mixing ratio, or on environmental conditions. Predicting long-term effects on the dynamics of plant communities requires an understanding of the interactions involved. The present experiment was designed to determine the effects of ozone on grassland species in relation to mixing ratio and soil water content (irrigation) using binary mixtures. The grass Trisetum flavescens was grown in potted replacement-series mixtures with Centaurea jacea (Experiment A) or Trifolium pratense (Experiment B). The plants were exposed to three concentrations of ozone in open-top chambers in two irrigation treatments. Total above-ground dry weight over three growth periods was measured. The competitive ability of T. flavescens was expressed as the competitive ratio ( CR _T). In Experiment B, total above-ground dry weight was reduced by elevated ozone and by reduced soil moisture, and significant interactions were found for ozone × irrigation and ozone × ratio. In Experiment A these effects were not significant. Under well watered conditions, CR _T tended to be reduced by elevated ozone in Experiment A, but increased significantly in Experiment B, indicating the importance of the competing species in modifying the ozone effect on T. flavescens . In both experiments reduced irrigation decreased the magnitude of ozone effects on biomass production, which could be related to observed reductions in specific leaf conductance. The results suggest that under well watered conditions the effect of elevated ozone on the competitive balance between species depends on the species mixture, but that the mixing ratio is less important.     

Negotiation and appeasement can be more effective drivers of sociality than kin selection

Two alternative frameworks explain the evolution of cooperation in the face of conflicting interests. Conflicts can be alleviated by kinship, the alignment of interests by virtue of shared genes, or by negotiation strategies, allowing mutually beneficial trading of services or commodities. Although negotiation often occurs in kin-structured populations, the interplay of kin- and negotiation-based mechanisms in the evolution of cooperation remains an unresolved issue. Inspired by the biology of a cooperatively breeding fish, we developed an individual-based simulation model to study the evolution of negotiation-based cooperation in relation to different levels of genetic relatedness. We show that the evolution of negotiation strategies leads to an equilibrium where subordinates appease dominants by conditional cooperation, resulting in high levels of help and low levels of aggression. This negotiation-based equilibrium can be reached both in the absence of relatedness and in a kin-structured population. However, when relatedness is high, evolution often ends up in an alternative equilibrium where subordinates help their kin unconditionally. The level of help at this kin-selected equilibrium is considerably lower than at the negotiation-based equilibrium, and it corresponds to a level reached when responsiveness is prevented from evolving in the simulations. A mathematical invasion analysis reveals that, quite generally, the alignment of payoffs due to the relatedness of interaction partners tends to impede selection for harsh but effective punishment of defectors. Hence kin structure will often hamper rather than facilitate the evolution of productive cooperation.     

Changes of proteins induced by anticoagulants can be more sensitively detected in urine than in plasma

The most fundamental property of biomarkers is change. But changes are hard to maintain in plasma since it is strictly controlled by homeostatic mechanisms of the body. There is no homeostatic mechanism for urine. Besides, urine is partly a filtration of blood, and systematic information can be reflected in urine. We hypothesize that change of blood can be reflected in urine more sensitively. Here we introduce the interference into the blood by two anticoagulants heparin or argatroban. Plasma and urine proteins were profiled by LC-MS/MS and then validated by Western blot in totally six SD female rats before and after the drug treatments. In argatroban treated group, with exactly the same experimental procedure and the same cutoff value for both plasma and urine proteins, 62 proteins changed in urine, only one of which changed in plasma. In heparin treated group, 27 proteins changed in urine but only three other proteins changed in plasma. Both LC-MS/MS and Western blot analyses demonstrated drug-induced increases in transferrin and hemopexin levels in urine but not in plasma. Our data indicates that urine may serve as a source for more sensitive detection of protein biomarkers than plasma.     

Evolutionary potential in the wild: more than meets the eye

The genus Aquilegia consists of 60–70 perennial plant species widely distributed throughout the northern hemisphere. Its flowers have a delicate and ornamental appearance that makes them a favourite of gardeners. In this genus, adaptive radiations for both floral and vegetative traits have occurred. These adaptive radiations, and the key phylogenetic placement of Aquilegia between Arabidopsis and rice, make this genus a ‘model system’ for plant evolution ( Kramer 2009 ). In this issue, Castellanos et al. (2011) use a marker‐based method to infer heritability for floral and vegetative traits in two Aquilegia species. Layered on top of this are estimates of the strength of natural selection. This novel joint estimation of heritability and selection in the wild showed that vegetative traits, compared to floral traits, have the highest evolutionarily potential. Evolutionary potential is the most important quantity to measure in wild populations. It combines inheritance and strength of selection and predicts the potential for populations to adapt to changing environments. The combination of molecular techniques with species in natural environments makes this work a model for molecular ecological investigations.     

Efficient generation of transgenic barley: The way forward to modulate plant–microbe interactions

Stable genetic transformation represents the gold standard approach to the detailed elucidation of plant gene functions. This is particularly relevant in barley, an important experimental model widely employed in applied molecular, genetic and cell biological research, and biotechnology. Presented are details of the establishment of a protocol for Agrobacterium-mediated gene transfer to immature embryos, which enables the highly efficient generation of transgenic barley. Advancements were achieved through comparative experiments on the influence of various explant treatments and co-cultivation conditions. The analysis of representative numbers of transgenic lines revealed that the obtained T-DNA copy numbers are typically low, the generative transmission of the recombinant DNA is in accordance with the Mendelian rules and the vast majority of the primary transgenics produce progeny that expresses the respective transgene product. Moreover, the newly established protocol turned out to be useful to transform not only the highly amenable cultivar (cv.) ‘Golden Promise’ but also other spring and winter barley genotypes, albeit with substantially lower efficiency. As a major result of this study, a very useful tool is now available for future functional gene analyses as well as genetic engineering approaches. With the aim to modify the expression of barley genes putatively involved in plant–fungus interactions, numerous transgenic plants have been generated using diverse expression cassettes. These plants represent an example of how transformation technology may contribute to further our understanding of important biological processes.     

Chloroplast: the Trojan horse in plant–virus interaction

The chloroplast is one of the most dynamic organelles of a plant cell. It carries out photosynthesis, synthesizes major phytohormones, plays an active part in the defence response and is crucial for interorganelle signalling. Viruses, on the other hand, are extremely strategic in manipulating the internal environment of the host cell. The chloroplast, a prime target for viruses, undergoes enormous structural and functional damage during viral infection. Indeed, large proportions of affected gene products in a virus‐infected plant are closely associated with the chloroplast and the process of photosynthesis. Although the chloroplast is deficient in gene silencing machinery, it elicits the effector‐triggered immune response against viral pathogens. Virus infection induces the organelle to produce an extensive network of stromules which are involved in both viral propagation and antiviral defence. From studies over the last few decades, the involvement of the chloroplast in the regulation of plant–virus interaction has become increasingly evident. This review presents an exhaustive account of these facts, with their implications for pathogenicity. We have attempted to highlight the intricacies of chloroplast–virus interactions and to explain the existing gaps in our current knowledge, which will enable virologists to utilize chloroplast genome‐based antiviral resistance in economically important crops.