Evolutionary patchwork of an insecticidal toxin shared between plant-associated pseudomonads and the insect pathogens Photorhabdus and Xenorhabdus.

BACKGROUND: Root-colonizing fluorescent pseudomonads are known for their excellent abilities to protect plants against soil-borne fungal pathogens. Some of these bacteria produce an insecticidal toxin (Fit) suggesting that they may exploit insect hosts as a secondary niche. However, the ecological relevance of insect toxicity and the mechanisms driving the evolution of toxin production remain puzzling. RESULTS: Screening a large collection of plant-associated pseudomonads for insecticidal activity and presence of the Fit toxin revealed that Fit is highly indicative of insecticidal activity and predicts that Pseudomonas protegens and P. chlororaphis are exclusive Fit producers. A comparative evolutionary analysis of Fit toxin-producing Pseudomonas including the insect-pathogenic bacteria Photorhabdus and Xenorhadus, which produce the Fit related Mcf toxin, showed that fit genes are part of a dynamic genomic region with substantial presence/absence polymorphism and local variation in GC base composition. The patchy distribution and phylogenetic incongruence of fit genes indicate that the Fit cluster evolved via horizontal transfer, followed by functional integration of vertically transmitted genes, generating a unique Pseudomonas-specific insect toxin cluster. CONCLUSIONS: Our findings suggest that multiple independent evolutionary events led to formation of at least three versions of the Mcf/Fit toxin highlighting the dynamic nature of insect toxin evolution.

Characterization of an antennal carboxylesterase from the pest moth Spodoptera littoralis degrading a host plant odorant.

Background: Carboxyl/cholinesterases (CCEs) are highly diversified in insects. These enzymes have a broad range of proposed functions, in neuro/developmental processes, dietary detoxification, insecticide resistance or hormone/pheromone degradation. As few functional data are available on purified or recombinant CCEs, the physiological role of most of these enzymes is unknown. Concerning their role in olfaction, only two CCEs able to metabolize sex pheromones have been functionally characterized in insects. These enzymes are only expressed in the male antennae, and secreted into the lumen of the pheromone-sensitive sensilla. CCEs able to hydrolyze other odorants than sex pheromones, such as plant volatiles, have not been identified. Methodology: In Spodoptera littoralis, a major crop pest, a diversity of antennal CCEs has been previously identified. We have employed here a combination of molecular biology, biochemistry and electrophysiology approaches to functionally characterize an intracellular CCE, SlCXE10, whose predominant expression in the olfactory sensilla suggested a role in olfaction. A recombinant protein was produced using the baculovirus system and we tested its catabolic properties towards a plant volatile and the sex pheromone components. Conclusion: We showed that SlCXE10 could efficiently hydrolyze a green leaf volatile and to a lesser extent the sex pheromone components. The transcript level in male antennae was also strongly induced by exposure to this plant odorant. In antennae, SlCXE10 expression was associated with sensilla responding to the sex pheromones and to plant odours. These results suggest that a CCE-based intracellular metabolism of odorants could occur in insect antennae, in addition to the extracellular metabolism occurring within the sensillar lumen. This is the first functional characterization of an Odorant- Degrading Enzyme active towards a host plant volatile.

Aluminium fouling and its impact on activated carbon based dioxin and furan removal in a wet scrubber at a co-incineration plant

Dioxins and furans, PCDD/Fs, are highly toxic substances formed in post combustion zones in furnaces. PCDD/F emissions are regulated by a waste incineration directive which relates also to co-incineration plants. Several observations of dioxin and furan enhancements in wet scrub- bers have been reported previously. This is thought to be due to the so-called "memory effect" which occurs when dioxins and furans absorb into plastic material in scrubbers and desorb when ambient circumstances alter significantly. At the co-incineration plant involved, dioxins and furans are controlled with a wet scrubber, the tower packing of which is made of plastic in which activated carbon particles are dispersed. This should avoid the memory effect and act as a dioxin and furan sink since dioxins and furans are absorbed irreversibly into the packing ma- terial. In this case, the tower packing in the scrubber is covered with a white layer that has been found to be mainly aluminium. The aim of this thesis was to determine the aluminium balance and the dioxin and furan behaviour in the scrubber and, thus, the impacts that the foul- ing has on dioxin and furan removal. The source of aluminium, reasons for fouling and further actions to minimize its impacts on dioxin and furan removal were also to be discovered. Measurements in various media around the scrubber and in fuels were made and a profile analysis of PCDD/F and mass balance calculations were carried out. PCDD/F content de- creased in the scrubber. The reduced PCDD/F was not discharged into scrubbing water. The removal mechanism seems to work in spite of the fouling, at least with low PCDD/F loads. Most of the PCDD/F in excess water originates from the Kymijoki River which is used as feeding water in the scrubber. Fouling turned out to consist mainly of aluminium hydroxides. Sludge combusted in the furnace was found to be a significant source of aluminium. Ways to minimize the fouling would be adjustment of pH to a proper lever, installation of a mechanical filter to catch the loose material from the scrubbing water and affecting the aluminium content of the sludge.

The Optimisation of the Draft Tube of a Hydro Power Plant at Off-Design Conditions

Several possible methods of increasing the efficiency and power of hydro power plants by improving the flow passages are investigated in this stydy. The theoretical background of diffuser design and its application to the optimisation of hydraulic turbine draft tubes is presented in the first part of this study. Several draft tube modernisation projects that have been carried out recently are discussed. Also, a method of increasing the efficiency of the draft tube by injecting a high velocity jet into the boundary layer is presented. Methods of increasing the head of a hydro power plant by using an ejector or a jet pump are discussed in the second part of this work. The theoretical principles of various ejector and jet pump types are presented and four different methods of calculating them are examined in more detail. A self-made computer code is used to calculate the gain in the head for two example power plants. Suitable ejector installations for the example plants are also discussed. The efficiency of the ejector power was found to be in the range 6 - 15 % for conventional head increasers, and 30 % for the jet pump at its optimum operating point. In practice, it is impossible to install an optimised jet pump with a 30 % efficiency into the draft tube as this would considerabely reduce the efficiency of the draft tube at normal operating conditions. This demonstrates, however, the potential for improvement which lies in conventional head increaser technology. This study is based on previous publications and on published test results. No actual laboratory measurements were made for this study. Certain aspects of modelling the flow in the draft tube using computational fluid dynamics are discussed in the final part of this work. The draft tube inlet velocity field is a vital boundary condition for such a calculation. Several previously measured velocity fields that have successfully been utilised in such flow calculations are presented herein.

Plant Immune Responses: Aphids Strike Back.

To survive and complete their life cycle, herbivorous insects face the difficult challenge of coping with the arsenal of plant defences. A new study reports that aphids secrete evolutionarily conserved cytokines in their saliva to suppress host immune responses.

Tracking the ghost of coevolution in specific plant-insect interactions : the case of the pollination system between the globeflower Trollius europaeus and seven european Chiastocheta flies

This study aims at understanding the evolutionary processes at work in specialized species interactions. Prom the macroevolutionary perspective, coevolution among specialized taxa was proposed to be one of the major processes generating biodiversity. We challenge this idea from the theoretical and practical perspective and through a literature review and show that the major hypotheses linking coevolutionary process with macroevolutionary patterns do not necessarily predict lineage co diversification and parallel speciation, limit¬ing the utility of the comparative phylogenenetic approach for investigating coevolution¬ary processes. We also point to the rarity of observed long-term coevolutionary dynamics among lineages and propose that coevolution rather occurs in shorter timescales, followed by ecological fitting. Prom the empirical point, we focus on the nursery pollination interaction between the European globeflower Trollius europaeus (Ranunculaceae) and its associated Chiastocheta flies (Anthomyiidae; Diptera) as a model system of evolution and maintenance of special¬ized interactions. The flies are obligate parasites of the seeds, but also pollinate the plant - it was thus proposed that both species are mutually dependent. Contrasting with the paradigm used for two decades of research on this system, we show that the female fitness component of the plant is similar in the populations with and without Chiastocheta. The plant is thus not exclusively dependent on the flies for reproduction. We discuss this result in the context of the factors responsible for the evolution of mutualistic systems. Understanding the evolution of a biological system requires understanding of its phylo- genetic context. Previous studies showed large mismatch between mtDNA phylogeny and morphological taxonomy in Chiastocheta. By using a large set of RAD-sequencing loci, we delineate the species limits that are congruent with morphology, and show that the discordance is best explained by the scenario of mitochondrial capture among fly species. Finally, we examine this system from a phylogeographic perspective, and identify the lack of congruence in spatial genetic structures of the plant and associated insects across their whole geographic range. The flies show lower numbers of spatial genetic groups than the plant, indicating that not all of the plant réfugia were shared by all the fly species or that the migration dynamics homogenized some of the groups. The incongruence in spatial genetic patterns indicates that fly migrations were largely independent from the genetic background of the plant, following rather a scenario of resource tracking, without the signature of coevolutionary process at this scale. Indeed, while the flies require the plant to survive climatic oscillations, the opposite is not true. Eventually, we show that there is no phylogenetic signal of spatial genetic structures, meaning that neither histories nor life- history traits are shared among closely related species and that species are characterized by unique trajectories of their genes. -- Cette étude vise à comprendre les processus évolutifs à l'oeuvre au sein d'interactions en¬tre espèces spécialisées. Du point de vue macroévolutif, la coévolution entre les taxons spécialisée a été considérée comme l'un des principaux processus générateur de biodiversité. Nous contestons cette idée du point de vue théorique et pratique à travers une revue de la littérature. Nous montrons que les hypothèses majeures reliant les processus coévolutifs avec les patterns de diversité au niveau macroévolutif ne prédisent pas nécessairement la co- diversification des lignées et leur spéciation parallèle, ce qui limite l'utilité de l'approche de phylogénie comparative pour étudier les processus coévolutifs . Nous rappelons également le peu d'exemples de dynamique coévolutive à long terme et proposons que la coévolution se produit plutôt dans des intervalles courts, suivis d'ajustements écologiques. Du point empirique, nous nous concentrons sur l'interaction de pollinisation entre le Trolle d'Europe Trollius europaeus (Ranunculaceae) et ses pollinisateurs associés, du genre Chiastocheta (Anthomyiidae; Diptera) en tant que système-modèle pour étudier l'évolution et le maintien des interactions spécialisées. Les mouches sont des parasites obligatoires des semences, mais pollinisent également la plante. Il a donc été proposé que les deux espèces soient mutuellement dépendantes. Contrastant avec le paradigme utilisé pendant deux décennies de recherche sur ce système, nous montrons, que la composante de fitness femelle de la plante est similaire dans les populations avec et sans Chiastocheta. La plante ne dépend donc pas exclusivement de son interaction avec les mouches pour la reproduction. Nous discutons de ce résultat dans le contexte des facteurs responsables de l'évolution des systèmes mutualistes. Comprendre l'évolution d'un système biologique nécessite la compréhension de son con- texte phylogénétique. Des études antérieures ont montré, chez Chiastocheta, de grandes disparités entre les phylogénies obtenues à partir d'ADN mitochondrial et la taxonomie basée sur les critères morphologiques. En utilisant un grand nombre de loci obtenus par RAD-sequencing, nous traçons les limites des espèces, qui concordent avec les car¬actéristiques morphologies, et montrons que la discordance s'explique en fait par un scénario de capture mitochondriale entre espèces de mouches. Enfin, nous examinons le système d'un point de vue phylogéographique, et identi¬fions les incohérences entre structurations génétiques spatiales de la plante et des insectes associés dans toute leur aire de distribution géographique. Les mouches présentent un nombre de groupes génétiques inférieur à la plante, indiquant que tous les refuges de la plante n'étaient pas partagés par toutes les espèces de mouches ou que les dynamiques migratoires ont homogénéisés certains des groupes chez les mouches. Les différences ob¬servées dans les patrons de structuration génétique spatiale indique que les migrations et dispersions des mouches ont été indépendantes du contexte génétique de la plante, et ces dernières ont été uniquement tributaires de la disponibilité des ressources, sans qu'il n'y ait de signature du processus de coévolution à cette échelle. En effet, tandis que les mouches ont besoin de la plante pour survivre aux oscillations climatiques, le contraire n'est pas exact. Finalement, nous montrons qu'il n'y a pas de signal phylogénétique des structurations génétiques spatiales chez les mouches, ce qui signifie que ni l'histoire, ni les traits d'histoire de vie ne sont partagés entre les espèces phylogénétiquement proches et que les espèces sont caractérisées par des trajectoires uniques de leurs gènes.

Fifty years after Ehrlich and Raven, is there support for plant-insect coevolution as a major driver of species diversification?

Since Ehrlich & Raven's seminal paper 50 years ago, coevolution has been seen as a major driver of species diversification. Here, we review classical and more recent case studies on the coevolution of plants and associated insects, to examine whether the coevolutionary component holds as an explanation of their current diversity. We discuss the main dogmas in coevolution and argue that coevolutionary processes should not be considered as major drivers of diversification in plants and insects. Instead, we suggest that coevolution essentially occurs through relatively short 'interludes', making the pattern difficult to detect. We also criticize the use of comparative phylogenetics to investigate coevolutionary processes, as coevolution may not necessarily produce congruent phylogenies among interacting lineages and, in turn, other processes may produce patterns of codivergence. Finally, we propose new lines of investigation for future research.

Molecular basis and regulation of insect pathogenicity in plant-beneficial pseudomonads

Les bactéries du genre Pseudomonas ont la capacité étonnante de s'adapter à différents habitats et d'y survivre, ce qui leur a permis de conquérir un large éventail de niches écologiques et d'interagir avec différents organismes hôte. Les espèces du groupe Pseudomonas fluorescens peuvent être facilement isolées de la rhizosphère et sont communément connues comme des Pseudomonas bénéfiques pour les plantes. Elles sont capables d'induire la résistance systémique des plantes, d'induire leur croissance et de contrer des phytopathogènes du sol. Un sous-groupe de ces Pseudomonas a de plus développé la capacité d'infecter et de tuer certaines espèces d'insectes. Approfondir les connaissances sur l'interaction de ces bactéries avec les insectes pourraient conduire au développement de nouveaux biopesticides pour la protection des cultures. Le but de cette thèse est donc de mieux comprendre la base moléculaire, l'évolution et la régulation de la pathogénicité des Pseudomonas plante-bénéfiques envers les insectes. Plus spécifiquement, ce travail a été orienté sur l'étude de la production de la toxine insecticide appelée Fit et sur l'indentification d'autres facteurs de virulence participant à la toxicité de la bactérie envers les insectes. Dans la première partie de ce travail, la régulation de la production de la toxine Fit a été évaluée par microscopie à épifluorescence en utilisant des souches rapportrices de Pseudomonas protegens CHA0 qui expriment la toxine insecticide fusionnée à une protéine fluorescente rouge, au site natif du gène de la toxine. Celle-ci a été détectée uniquement dans l'hémolymphe des insectes et pas sur les racines des plantes, ni dans les milieux de laboratoire standards, indiquant une production dépendante de l'hôte. L'activation de la production de la toxine est contrôlée par trois protéines régulatrices dont l'histidine kinase FitF, essentielle pour un contrôle précis de l'expression et possédant un domaine "senseur" similaire à celui de la kinase DctB qui régule l'absorption de carbone chez les Protéobactéries. Il est donc probable que, durant l'évolution de FitF, un réarrangement de ce domaine "senseur" largement répandu ait contribué à une production hôte-spécifique de la toxine. Les résultats de cette étude suggèrent aussi que l'expression de la toxine Fit est plutôt réprimée en présence de composés dérivés des plantes qu'induite par la perception d'un signal d'insecte spécifique. Dans la deuxième partie de ce travail, des souches mutantes ciblant des facteurs de virulence importants identifiés dans des pathogènes connus ont été générées, dans le but d'identifier ceux avec une virulence envers les insectes atténuée. Les résultats ont suggéré que l'antigène O du lipopolysaccharide (LPS) et le système régulateur à deux composantes PhoP/PhoQ contribuent significativement à la virulence de P. protegens CHA0. La base génétique de la biosynthèse de l'antigène O dans les Pseudomonas plante-bénéfiques et avec une activité insecticide a été élucidée et a révélé des différences considérables entre les lignées suite à des pertes de gènes ou des acquisitions de gènes par transfert horizontal durant l'évolution de certaines souches. Les chaînes latérales du LPS ont été montrées comme vitales pour une infection des insectes réussie par la souche CHA0, après ingestion ou injection. Les Pseudomonas plante-bénéfiques, avec une activité insecticide sont naturellement résistants à la polymyxine B, un peptide antimicrobien modèle. La protection contre ce composé antimicrobien particulier dépend de la présence de l'antigène O et de la modification du lipide A, une partie du LPS, avec du 4-aminoarabinose. Comme les peptides antimicrobiens cationiques jouent un rôle important dans le système immunitaire des insectes, l'antigène O pourrait être important chez les Pseudomonas insecticides pour surmonter les mécanismes de défense de l'hôte. Le système PhoP/PhoQ, connu pour contrôler les modifications du lipide A chez plusieurs bactéries pathogènes, a été identifié chez Pseudomonas chlororaphis PCL1391 et P. protegens CHA0. Pour l'instant, il n'y a pas d'évidence que des modifications du lipide A contribuent à la pathogénicité de cette bactérie envers les insectes. Cependant, le senseur-kinase PhoQ est requis pour une virulence optimale de la souche CHA0, ce qui suggère qu'il régule aussi l'expression des facteurs de virulence de cette bactérie. Les découvertes de cette thèse démontrent que certains Pseudomonas associés aux plantes sont de véritables pathogènes d'insectes et donnent quelques indices sur l'évolution de ces microbes pour survivre dans l'insecte-hôte et éventuellement le tuer. Les résultats suggèrent également qu'une recherche plus approfondie est nécessaire pour comprendre comment ces bactéries sont capables de contourner ou surmonter la réponse immunitaire de l'hôte et de briser les barrières physiques pour envahir l'insecte lors d'une infection orale. Pour cela, les futures études ne devraient pas uniquement se concentrer sur le côté bactérien de l'interaction hôte-microbe, mais aussi étudier l'infection du point de vue de l'hôte. Les connaissances gagnées sur la pathogénicité envers les insectes des Pseudomonas plante-bénéfiques donnent un espoir pour une future application en agriculture, pour protéger les plantes, non seulement contre les maladies, mais aussi contre les insectes ravageurs. -- Pseudomonas bacteria have the astonishing ability to survive within and adapt to different habitats, which has allowed them to conquer a wide range of ecological niches and to interact with different host organisms. Species of the Pseudomonas fluorescens group can readily be isolated from plant roots and are commonly known as plant-beneficial pseudomonads. They are capable of promoting plant growth, inducing systemic resistance in the plant host and antagonizing soil-borne phytopathogens. A defined subgroup of these pseudomonads evolved in addition the ability to infect and kill certain insect species. Profound knowledge about the interaction of these particular bacteria with insects could lead to the development of novel biopesticides for crop protection. This thesis thus aimed at a better understanding of the molecular basis, evolution and regulation of insect pathogenicity in plant-beneficial pseudomonads. More specifically, it was outlined to investigate the production of an insecticidal toxin termed Fit and to identify additional factors contributing to the entomopathogenicity of the bacteria. In the first part of this work, the regulation of Fit toxin production was probed by epifluorescence microscopy using reporter strains of Pseudomonas protegens CHAO that express a fusion between the insecticidal toxin and a red fluorescent protein in place of the native toxin gene. The bacterium was found to express its insecticidal toxin only in insect hemolymph but not on plant roots or in common laboratory media. The host-dependent activation of Fit toxin production is controlled by three local regulatory proteins. The histidine kinase of this regulatory system, FitF, is essential for the tight control of toxin expression and shares a sensing domain with DctB, a sensor kinase regulating carbon uptake in Proteobacteria. It is therefore likely that shuffling of a ubiquitous sensor domain during the evolution of FitF contributed to host- specific production of the Fit toxin. Findings of this study additionally suggest that host-specific expression of the Fit toxin is mainly achieved by repression in the presence of plant-derived compounds rather than by induction upon perceiving an insect-specific signal molecule. In the second part of this thesis, mutant strains were generated that lack factors previously shown to be important for virulence in prominent pathogens. A screening for attenuation in insect virulence suggested that lipopolysaccharide (LPS) O-antigen and the PhoP-PhoQ two-component regulatory system significantly contribute to virulence of P. protegens CHAO. The genetic basis of O-antigen biosynthesis in plant-beneficial pseudomonads displaying insect pathogenicity was elucidated and revealed extensive differences between lineages due to reduction and horizontal acquisition of gene clusters during the evolution of several strains. Specific 0 side chains of LPS were found to be vital for strain CHAO to successfully infect insects by ingestion or upon injection. Insecticidal pseudomonads with plant-beneficial properties were observed to be naturally resistant to polymyxin B, a model antimicrobial peptide. Protection against this particular antimicrobial compound was dependent on the presence of O-antigen and modification of the lipid A portion of LPS with 4-aminoarabinose. Since cationic antimicrobial peptides play a major role in the immune system of insects, O-antigenic polysaccharides could be important for insecticidal pseudomonads to overcome host defense mechanisms. The PhoP-PhoQ system, which is well-known to control lipid A modifications in several pathogenic bacteria, was identified in Pseudomonas chlororaphis PCL1391 and P. protegens CHAO. No evidence was found so far that lipid A modifications contribute to insect pathogenicity in this bacterium. However, the sensor kinase PhoQ was required for full virulence of strain CHAO suggesting that it additionally regulates the expression of virulence factors in this bacterium. The findings of this thesis demonstrate that certain plant-associated pseudomonads are true insect pathogens and give some insights into how these microbes evolved to survive within and eventually kill the insect host. Results however also point out that more in-depth research is needed to know how exactly these fascinating bacteria manage to bypass or overcome host immune responses and to breach physical barriers to invade insects upon oral infection. To achieve this, future studies should not only focus on the bacterial side of the microbe-host interactions but also investigate the infection from a host-oriented view. The knowledge gained about the entomopathogenicity of plant-beneficial pseudomonads gives hope for their future application in agriculture to protect plants not only against plant diseases but also against insect pests.

Introgressive hybridization of threatened European tree frogs (Hyla arborea) by introduced H. intermedia in Western Switzerland

Hybridization by introduced taxa is a major threat to native species. Characterizing human introductions is thus one of the missions of conservation geneticists. Here we survey a declining population of the regionally endangered European tree frog (Hyla arborea) in the Grangettes natural reserve (Rhone valley, Western Switzerland), where previous evidence indicated human introduction of the Italian taxon H. intermedia. We combined fast-evolving mitochondrial and nuclear markers and an extended sampling to conduct population genetic analyses of the Grangettes and putative source areas. We show that the Grangettes population is a hybrid swarm, with all individuals featuring recent nuclear admixture and mitochondrial DNA of introduced H. intermedia, most likely of proximate south Alpine origin. In contrast, H. arborea and H. intermedia hardly introgress in their natural parapatric ranges, consistent with an advanced reproductive isolation. Thus, potential hybrid incompatibilities may account for the strong decline of this population, despite important conservation efforts. Although their hybrid nature makes them a priori unworthy of any protection, we propose specific measures to recover local H. arborea gene pool and preserve tree frogs in the Grangettes, the last population remaining from this heavily impacted part of the Alps.

Missing pieces in the puzzle of plant microRNAs.

Plant microRNAs (miRNAs) are important regulatory switches. Recent advances have revealed many regulatory layers between the two essential processes, miRNA biogenesis and function. However, how these multilayered regulatory processes ultimately control miRNA gene regulation and connects miRNAs and plant responses with the surrounding environment is still largely unknown. In this opinion article, we propose that the miRNA pathway is highly dynamic and plastic. The apparent flexibility of the miRNA pathway in plants appears to be controlled by a number recently identified proteins and poorly characterized signaling cascades. We further propose that altered miRNA accumulation can be a direct consequence of the rewiring of interactions between proteins that function in the miRNA pathway, an avenue that remains largely unexplored.

Disjunct populations of European vascular plant species keep the same climatic niches

Aim Previous research on how climatic niches vary across species ranges has focused on a limited number of species, mostly invasive, and has not, to date, been very conclusive. Here we assess the degree of niche conservatism between distant populations of native alpine plant species that have been separated for thousands of years. Location European Alps and Fennoscandia. Methods Of the studied pool of 888 terrestrial vascular plant species occurring in both the Alps and Fennoscandia, we used two complementary approaches to test and quantify climatic-niche shifts for 31 species having strictly disjunct populations and 358 species having either a contiguous or a patchy distribution with distant populations. First, we used species distribution modelling to test for a region effect on each species' climatic niche. Second, we quantified niche overlap and shifts in niche width (i.e. ecological amplitude) and position (i.e. ecological optimum) within a bi-dimensional climatic space. Results Only one species (3%) of the 31 species with strictly disjunct populations and 58 species (16%) of the 358 species with distant populations showed a region effect on their climatic niche. Niche overlap was higher for species with strictly disjunct populations than for species with distant populations and highest for arctic-alpine species. Climatic niches were, on average, wider and located towards warmer and wetter conditions in the Alps. Main conclusion Climatic niches seem to be generally conserved between populations that are separated between the Alps and Fennoscandia and have probably been so for 10,000-15,000 years. Therefore, the basic assumption of species distribution models that a species' climatic niche is constant in space and time - at least on time scales 104 years or less - seems to be largely valid for arctic-alpine plants.

Plant polyamines in stress and development: an emerging area of research in plant sciences.

Compelling evidence indicates the participation of polyamines in abiotic and biotic stress responses in plants. Indeed, genetic engineering of polyamine levels in plants has successfully improved biotic and abiotic stress resistance in model plants and crops. We anticipate that many of the current challenges in agriculture to cope with climate change and maintain nutritional quality of fruits and vegetables can be approached by considering the polyamine pathway...