Role of local climate and interspecific competition in the limitation of the invaded area of Ambrosia artemisiifolia L. in Western Europe

Le processus d’invasion est fondamentalement inscrit dans une dynamique temporelle et peut être décrit comme un phénomène durant lequel une espèce franchit différentes barrières. Une espèce doit en premier lieu franchir une « barrière géographique » pour être introduite dans un nouveau territoire. Une fois introduite, l’espèce doit survivre aux nouvelles conditions environnementales et être capable de se reproduire, afin de former des populations viables. Elle passe alors la « barrière environnementale » et peut être considérée comme naturalisée. Enfin, elle doit encore franchir la « barrière de la dispersion » et se répandre dans l’environnement pour être considérée comme une espèce invasive. En outre, sur un continent, une espèce peut être à différents stades de franchissement de ces barrières en fonction de la région considérée. On peut ainsi trouver, en fonction des zones géographiques, des populations non–naturalisées qui ne parviennent pas à se maintenir sans apport de propagules, des populations naturalisées, mais qui ne sont pas invasives, et des populations invasives. Cette variation géographique peut résulter, entre autres, d’une variation des conditions environnementales à l’échelle du continent. L’invasion de l’ambroisie à feuilles d’armoise (Ambrosia artemisiifolia L.) constitue une excellente opportunité d’étudier cet aspect de la biologie des invasions. En effet, l’historique d’invasion et la répartition actuelle de l’espèce sont bien documentés, et mettent en évidence des variations géographiques dans la dynamique d’invasion. En Europe de l’Ouest par exemple, il existe des régions fortement envahies (comme la vallée du Rhône, en France) et des régions où l’espèce n’est pas considérée comme naturalisée ou invasive, plus au nord (comme le Nord de la France, la Belgique et les Pays-Bas). Dans ce travail de thèse, nous avons testé l’hypothèse que l’aire d’invasion actuelle d’A. artemisiifolia était limitée vers le Nord, du fait d’un climat local défavorable ou d’une compétition interspécifique trop importante. Afin d’atteindre cet objectif général, quatre questions ont été posées. 1) Le climat local et/ou la compétition interspécifique causent-ils une variation des performances des individus dans différentes zones de l’aire d’introduction en Europe de l’Ouest ? ; 2) Au nord des zones actuellement envahies, le climat permet-il à de nouvelles populations introduites dans un habitat agricole de se maintenir et de s’accroître ? ; 3) Quelle est l’importance de la variabilité morphologique des graines dans l’invasion de zones à climat rigoureux ? ; et 4) Quelle est l’importance de l’effet de priorité lors de l’établissement de l’espèce au sein d’une communauté rudérale ? Nos recherches ont abouti aux conclusions suivantes : ni le climat local, ni la compétition interspécifique ne semblent empêcher la naturalisation et la future progression de l’espèce au nord de l’aire actuelle d’invasion, que ce soit dans les habitats rudéraux ou agricoles. En situation agricole au nord de l’aire d’invasion actuelle, l’espèce est capable de former des populations dont la production de descendants est importante. En moyenne au cours de notre expérimentation, chaque plant a produit un nombre de descendants égal à 273 ± 18.4 (moyenne ± erreur standard). Dans les habitats rudéraux, des populations existent déjà en Belgique et dans le sud des Pays-Bas, et sont capables de produire une grande quantité de graines : en moyenne, les plants mesurés portaient 222 ± 32.0 graines. Les performances des individus de ces populations sont d’ailleurs similaires à celles des individus au centre du foyer d’invasion. Aucune limite à la colonisation des zones au nord de l’aire d’invasion actuelle n’a été mise en évidence dans ce travail. Ceci est cohérent avec les observations d’autres auteurs mettant en doute le statut « non-naturalisé » de l’espèce en Belgique, et illustre l’aspect dynamique de l’invasion. L’importance de la temporalité dans la colonisation des milieux perturbés apparait critique. Lorsque la plante se développe quelques semaines avant le reste de la communauté, elle bénéficie d’une augmentation de performances bien supérieure à ce que d’autres astéracées rudérales sont capables d’atteindre dans la même situation. Dans notre expérience, l’effet de priorité induisait une biomasse aérienne 30.5 ± 1.94 fois plus élevée, et un nombre d’inflorescences 570 ± 160 fois plus important. Par ailleurs, la grande variabilité de l’espèce joue probablement un rôle important dans le succès de l’invasion. Ainsi, la grande variabilité des graines augmente la gamme de conditions environnementales où l’espèce peut se développer. Nos observations laissent présager un potentiel d’invasion au nord de l’aire d’invasion actuelle. Dans cette situation incertaine, il nous apparait important de mettre en place un système de détection précoce de l’ambroisie, afin de permettre son éradication et cela, avant que l’invasion ne soit aussi problématique qu’en France. Des campagnes de sensibilisation du secteur public et agricole devraient être envisagées en Belgique, afin que de nouvelles occurrences de la plante ne passent pas inaperçues et que la propagation de l’espèce puisse être endiguée.The invasion process is classically described from a temporal point of view, where a species overcomes a defined number of barriers. First, a species has to get through the geographical barrier, i.e., be introduced in the new area. Once introduced, the species has to survive new environmental conditions and reproduce successfully. When the environmental barrier is overcome, i.e. when the species is able to reproduce and its populations are self-sufficient, it is considered as naturalized. To finally be considered as invasive, the species has to overcome the dispersal barrier and spread across landscapes. Within a given continent, a species could have overcome a variable number of barriers depending on the considered area. At a given moment, depending on the geographical area, one can observe non-naturalized populations, naturalized populations that are not invasive, and invasive populations. This geographical variation may be the result of an environmental variation across the continent. The common ragweed (Ambrosia artemisiifolia L.) invasion in Western Europe is a good opportunity to study this aspect of invasion biology. The invasion history and the species distribution are well documented, and highlight a geographical variation of the invasion dynamics. This is particularly clear in Western Europe, where there is a contrast between the highly invaded zone of the Rhône valley in France, and more northern areas such as the North of France, Belgium, and the Netherlands. In this work, we tested the hypothesis that the current invasion area is limited northwards, because of an unfavorable local climate or a too strong interspecific competition. In order to answer this general objective, four different questions were asked: 1) Is the climate and/or the interspecific competition causing a variation in plant performances across Western Europe?; 2) In an agricultural context north to the current invaded range, is the local climate allowing the establishment and the reproduction of newly introduced populations?; 3) What is the role of seed morphological variability in the invasion of areas with rigorous climatic conditions?; and 4) What is the role of the priority effect in the species establishment within a ruderal community? No clear limit to the colonization of areas beyond the current invaded range was found in this study. The local climate and the interspecific competition did not appear to limit the naturalization or spread of the species north to the current invaded range, be it in agricultural or ruderal situations. Results showed that once introduced in an agricultural habitat outside the current invaded range, the species was able to establish self-sustaining populations. On average, each plant produced a number of descendants equal to 273 ± 18.4 (mean ± standard error). In ruderal habitats, populations already exist in Belgium and in Southern Netherlands, and are able to produce a high quantity of seeds: on average, the measured plants carried 222 ± 32.0 seeds. The measured plant performances were similar to those measured within the invaded area. The findings of this work are consistent with those of other authors that questioned the “non-naturalized” species status in Belgium, and illustrate how temporally dynamic invasions are. The results showed the importance of the timing in the colonization of disturbed habitats. When the species started its development a few weeks before the rest of the community, its performance gain was higher than that of other ruderal Asteraceae species: its above ground biomass was 30.5 ± 1.94 times higher, and the number of flower heads 570 ± 160 times more important. The high variability of the species observed all along this work is probably playing an important role in the invasion success. The high morphological variability of the seeds seems to widen the range of environmental conditions the species is able to colonize. This study suggests a great invasion potential north to the current invaded area in Western Europe. In this uncertain situation, it appears critical to create an early detection system of the species in Belgium. Early detection may allow the eradication of the species before the invasion becomes as problematic as in France. Awareness campaigns should be encouraged in Belgium in order to avoid that new occurrences of the species remain unnoticed

A self-assembled luminescent host that selectively senses ATP in water.

Metal-ion-directed self-assembly has been used to construct kinetically inert, water-soluble heterometallic Ru2Re2 hosts that are potential sensors for bioanions. A previously reported metallomacrocycle and a new derivative synthesised by this approach are found to be general sensors for bioanions in water, showing an “off–on” luminescent change that is selective for nucleotides over uncharged nucleobases. Through a change in the ancillary ligands coordinated to the ruthenium centres of the host, an “off–on” sensor has been produced. Whilst this host only shows a modest enhancement in binding affinities for nucleotides relative to the other two host systems, its sensing response is much more specific. Although a distinctive “off–on” luminescence response is observed for the addition of adenosine triphosphosphate (ATP), related structures such as adenine and guanosine triphosphate (GTP) do not induce any emission change in the host. Detailed and demanding DFT studies on the ATP- and GTP-bound host–guest complexes reveal subtle differences in their geometries that modulate the stacking interactions between the nucleotide guests and the ancillary ligands of the host. It is suggested that this change in stacking geometries affects solvent accessibility to the binding pocket of the host and thus leads to observed difference in the host luminescence response to the guests

Photoactivated chemotherapy (PACT) : the potential of excited-state d-block metals in medicine

The fields of phototherapy and of inorganic chemotherapy both have long histories. Inorganic photoactivated chemotherapy (PACT) offers both temporal and spatial control over drug activation and has remarkable potential for the treatment of cancer. Following photoexcitation, a number of different decay pathways (both photophysical and photochemical) are available to a metal complex. These pathways can result in radiative energy release, loss of ligands or transfer of energy to another species, such as triplet oxygen. We discuss the features which need to be considered when developing a metal-based anticancer drug, and the common mechanisms by which the current complexes are believed to operate. We then provide a comprehensive overview of PACT developments for complexes of the different d-block metals for the treatment of cancer, detailing the more established areas concerning Ti, V, Cr, Mn, Re, Fe, Ru, Os, Co, Rh, Pt, and Cu and also highlighting areas where there is potential for greater exploration. Nanoparticles (Ag, Au) and quantum dots (Cd) are also discussed for their photothermal destructive potential. We also discuss the potential held in particular by mixed-metal systems and Ru complexes

Stabilization of long-looped i-motif DNA by polypyridyl ruthenium complexes

A spectroscopic study of the interactions of Λ- and Δ-[Ru(phen)2(dppz)]2+ with i-motif DNA containing thymine loops of various lengths. In the presence of i-motifs, the luminescence of the Λ enantiomer was enhanced much more than the Δ. Despite this, the effect of each enantiomer on i-motif thermal stability was comparable. The sequences most affected by [Ru(phen)2(dppz)]2+ were those with long thymine loops; this suggests that long-looped i-motifs are attractive targets for potential transition metal complex drugs and should be explored further in drug design

X-ray crystal structures show DNA stacking advantage of terminal nitrile substitution in Ru-dppz complexes

The new complexes [Ru(TAP)2(11-CN-dppz)]2+, [Ru(TAP)2(11-Br-dppz)]2+and [Ru(TAP)2(11,12-diCN-dppz)]2+ are reported. The addition of nitrile substituents to the dppz ligand of the DNA photooxidising complex [Ru(TAP)2(dppz)]2+ promote π-stacking interactions and ordered binding to DNA, as shown by X-ray crystallography. The structure of -[Ru(TAP)2(11-CN-dppz)]2+ with the DNA duplex d(TCGGCGCCGA)2 shows, for the first time with this class of complex, a closed intercalation cavity with an AT base pair at the terminus. The structure obtained is compared to that formed with the 11-Br and 11,12-dinitrile derivatives, highlighting the stabilization of syn guanine by this enantiomer when the terminal basepair is GC. In contrast the AT basepair has the normal Watson-Crick orientation, highlighting the difference in charge distribution between the two purine bases and the complementarity of the dppz-purine interaction. The asymmetry of the cavity highlights the importance of the purine-dppz-purine stacking interaction

Combined analysis of single cell RNA-Seq and ATAC-Seq data reveals putative regulatory toggles operating in native and iPS-derived retina.

We report the generation and analysis of single-cell RNA-Seq data (> 38,000 cells) from native and iPSC-derived murine retina at four matched developmental stages spanning the emergence of the major retinal cell types. We combine information from temporal sampling, visualization of 3D UMAP manifolds, pseudo-time and RNA velocity analyses, to show that iPSC-derived 3D retinal aggregates broadly recapitulate the native developmental trajectories. However, we show relaxation of spatial and temporal transcriptome control, premature emergence and dominance of photoreceptor precursor cells, and susceptibility of dynamically regulated pathways and transcription factors to culture conditions in iPSC-derived retina. We generate bulk ATAC-Seq data for native and iPSC-derived murine retina identifying ~125,000 peaks. We combine single-cell RNA-Seq with ATAC-Seq information and obtain evidence that approximately half the transcription factors that are dynamically regulated during retinal development may act as repressors rather than activators. We propose that sets of activators and repressors with cell-type specific expression constitute regulatory toggles that lock cells in distinct transcriptome states underlying differentiation. We provide evidence supporting our hypothesis from the analysis of publicly available single-cell ATAC-Seq data for adult mouse retina. We identify subtle but noteworthy differences in the operation of such toggles between native and iPSC-derived retina particularly for the Etv1, Etv5, Hes1 and Zbtb7a group of transcription factors

In Silico Analysis of the Apolipoprotein E and the Amyloid β Peptide Interaction: Misfolding Induced by Frustration of the Salt Bridge Network

The relationship between Apolipoprotein E (ApoE) and the aggregation processes of the amyloid β (Aβ) peptide has been shown to be crucial for Alzheimer's disease (AD). The presence of the ApoE4 isoform is considered to be a contributing risk factor for AD. However, the detailed molecular properties of ApoE4 interacting with the Aβ peptide are unknown, although various mechanisms have been proposed to explain the physiological and pathological role of this relationship. Here, computer simulations have been used to investigate the process of Aβ interaction with the N-terminal domain of the human ApoE isoforms (ApoE2, ApoE3 and ApoE4). Molecular docking combined with molecular dynamics simulations have been undertaken to determine the Aβ peptide binding sites and the relative stability of binding to each of the ApoE isoforms. Our results show that from the several ApoE isoforms investigated, only ApoE4 presents a misfolded intermediate when bound to Aβ. Moreover, the initial α-helix used as the Aβ peptide model structure also becomes unstructured due to the interaction with ApoE4. These structural changes appear to be related to a rearrangement of the salt bridge network in ApoE4, for which we propose a model. It seems plausible that ApoE4 in its partially unfolded state is incapable of performing the clearance of Aβ, thereby promoting amyloid forming processes. Hence, the proposed model can be used to identify potential drug binding sites in the ApoE4-Aβ complex, where the interaction between the two molecules can be inhibited

Photochemically active DNA-intercalating ruthenium and related complexes – insights by combining crystallography and transient spectroscopy

Recent research on the study of the interaction of ruthenium polypyridyl compounds and defined sequence nucleic acids is reviewed. Particular emphasis is paid to complexes [Ru(LL)2(Int)]2+ containing potentially intercalating ligands (Int) such as dipyridophenazine (dppz), which are known to display light-switching or photo-oxidising behaviour, depending on the nature of the ancillary ligands. X-ray crystallography has made a key contribution to our understanding, and the first complete survey of structural results is presented. These include sequence, enantiomeric, substituent and structural specificities. The use of ultrafast transient spectrocopic methods to probe the ultrafast processes for complexes such as [Ru(TAP)2(dppz)]2+ and [Ru(phen)2(dppz)]2+ when bound to mixed sequence oligonucleotides are reviewed with particular attention being paid to the complementary advantages of transient (visible) absorption and time-resolved (mid) infra-red techniques to probe spectral changes in the metal complex and in the nucleic acid. The observed photophysical properties are considered in light of the structural information obtained from X-ray crystallography. In solution, metal complexes can be expected to bind at more than one DNA step, so that a perfect correlation of the photophysical properties and factors such as the orientation or penetration of the ligand into the intercalation pocket should not be expected. This difficulty can be obviated by carrying out TRIR studies in the crystals. Dppz complexes also undergo insertion, especially with mismatched sequences. Future areas for study such as those involving non-canonical forms of DNA, such as G-quadruplexes or i-motifs are also briefly considered