Chiroptical properties of two chiral atropisomers of propeller‐like trityl‐based radical derivatives have been analyzed. A new absolute configuration (AC) assignment has been made, according to the ...combination of experimental and theoretical data. In this sense, their ACs have been determined through the comparison of the Cotton effects recorded by electronic circular dichroism (ECD) with the theoretical ECD of the open shell structures obtained by TD‐DFT calculations. Finally, their circularly polarized luminescence (CPL) responses have been addressed. Remarkably, this is the first description of organic free radicals as intrinsic CPL emitters. Opposite signed CPL has been detected for each pair of conformers, with acceptable luminescent dissymmetry factors (|glum|≈0.5–0.8×10−3) considering their pure organic nature. In fact, highly efficient chiral emissions have been demonstrated, according to the comparison of |glum| with their respective absorption anisotropy factors (|gabs|). This pioneering study lays the foundations for the optimization of new magnetically active organic chiral emitters.
Propeller‐like trityl‐based radical derivatives were employed to explore highly efficient intrinsic chiral emission from enantiomeric organic free radicals. This is the first description of organic free radicals as intrinsic circularly polarized luminescence emitters.
Summary
Feedback between plants and soil microbial communities can be a powerful driver of vegetation dynamics. Plants elicit changes in the soil microbiome that either promote or suppress ...conspecifics at the same location, thereby regulating population density‐dependence and species co‐existence. Such effects are often attributed to the accumulation of host‐specific antagonistic or beneficial microbiota in the rhizosphere. However, the identity and host‐specificity of the microbial taxa involved are rarely empirically assessed. Here we review the evidence for host‐specificity in plant‐associated microbes and propose that specific plant–soil feedbacks can also be driven by generalists. We outline the potential mechanisms by which generalist microbial pathogens, mutualists and decomposers can generate differential effects on plant hosts and synthesize existing evidence to predict these effects as a function of plant investments into defence, microbial mutualists and dispersal. Importantly, the capacity of generalist microbiota to drive plant–soil feedbacks depends not only on the traits of individual plants but also on the phylogenetic and functional diversity of plant communities. Identifying factors that promote specialization or generalism in plant–microbial interactions and thereby modulate the impact of microbiota on plant performance will advance our understanding of the mechanisms underlying plant–soil feedback and the ways it contributes to plant co‐existence.
A new family of distorted ribbon‐shaped nanographenes was designed, synthesized, and their optical and electrochemical properties were evaluated, pointing out an unprecedented correlation between ...their structural characteristics and the two‐photon absorption (TPA) responses and electrochemical band gaps. Three nanographene ribbons have been prepared: a seven‐membered‐ring‐containing nanographene presenting a tropone moiety at the edge, its full‐carbon analogue, and a purely hexagonal one. We have found that the TPA cross‐sections and the electrochemical band gaps of the seven‐membered‐ring‐containing compounds are higher and lower, respectively, than those of the fully hexagonal polycyclic aromatic hydrocarbon (PAH). Interestingly, the inclusion of additional curvature has a positive effect in terms of non‐linear optical properties of those ribbons.
The advantage of defects: The effect of a tropone moiety on the nonlinear optical properties of ribbon‐shaped nanographenes is unequivocally demonstrated. Curved edges created by the inclusion of heptagonal carbocycles enhance the two‐photon absorption on graphene molecules.
There is increasing knowledge on the diversity of root-endophytic fungi, but limited information on their lifestyles and dependence on hosts hampers our understanding of their ecological functions. ...We compared diversity and biogeographical patterns of cultivable and noncultivable root endophytes to assess whether their occurrence is determined by distinct ecological factors.
The endophytic diversity in roots of nonmycorrhizal Microthlaspi spp. growing across Europe was assessed using high-throughput sequencing (HTS) and compared with a previous dataset based on cultivation of endophytes from the same root samples.
HTS revealed a large fungal richness undetected by cultivation, but which largely comprised taxa with restricted distributions and/or low representation of sequence reads. Both datasets coincided in a consistent high representation of widespread endophytes within orders Pleosporales, Hypocreales and Helotiales, as well as similar associations of community structure with spatial and environmental conditions. Likewise, distributions of particular endophytes inferred by HTS agreed with cultivation data in suggesting individual ecological preferences.
Our findings support that Microthlaspi spp. roots are colonized mostly by saprotrophic and likely facultative endophytes, and that differential niche preferences and distribution ranges among fungi importantly drive the assembly of root-endophytic communities.
A new persistent organic free radical has been synthetized with Br atoms occupying the ortho‐ and para‐positions of a trityl core. After the isolation of its two propeller‐like atropisomers, Plus (P) ...and minus (M), their absolute configurations were assigned by a combination of theoretical and experimental data. Remarkably, no hints of racemization were observed up to 60 °C for more than two hours, due to the higher steric hindrance imposed by the bulky Br atoms. Therefore, when compared to its chlorinated homologue (t1/2=18 s at 60 °C), an outstanding stability against racemization was achieved. A circularly polarized luminescence (CPL) response of both enantiomers was detected. This free radical shows a satisfactory luminescent dissymmetry factor (|glum(592 nm)|≈0.7×10−3) despite its pure organic nature and low luminescence quantum yield (LQY). Improved organic magnetic CPL emitters derived from the reported structure can be envisaged thanks to the wide possibilities that Br atoms at para‐positions offer for further functionalization.
Get radical! An efficient circularly polarized luminescence emitter, based on a persistent trityl radical substituted with bulky bromine atoms at ortho‐ and para‐positions, is reported (see figure). In addition, this emitter has a high racemization barrier between its enantiomers.
A cyclophane is reported incorporating two units of a heptagon‐containing extended polycyclic aromatic hydrocarbon (PAH) analogue of the hexa‐peri‐hexabenzocoronene (HBC) moiety (hept‐HBC). This ...cyclophane represents a new class of macrocyclic structures that incorporate for the first time seven‐membered rings within extended PAH frameworks. The saddle curvature of the hept‐HBC macrocycle units induced by the presence of the nonhexagonal ring along with the flexible alkyl linkers generate a cavity with shape complementarity and appropriate size to enable π interactions with fullerenes. Therefore, the cyclophane forms host–guest complexes with C60 and C70 with estimated binding constants of Ka=420±2 m−1 and Ka=(6.49±0.23)×103 m−1, respectively. As a result, the macrocycle can selectively bind C70 in the presence of an excess of a mixture of C60 and C70.
Carbon nanobasket: A new cyclophane bearing two units of heptagon‐containing hexa‐peri‐hexabenzocoronene is presented. The macrocycle offers an unusual aromatic calix‐shaped cavity able to interact with fullerenes. The selective binding of C70 over C60 is demonstrated.
Root‐colonizing fungi form species‐rich assemblages with key functions in principal ecosystem processes, making them prospectively important players in conservation and applied ecology. Harnessing ...the processes and services they drive requires a better understanding of their patterns of diversity and community structure, and how these link to function. Here, we search for possible adaptations to contrasting environmental and host conditions, indicative of participation in habitat‐specific processes. We surveyed heathland and grassland habitats across a latitudinal gradient in Western Europe, using a spatially explicit design to assess community variation at scales from centimeters, to thousands of kilometers. Root‐associated fungi assemble into strongly site‐specific communities irrespective of habitat type, shaped by environmental factors and spatial distance operating at different scales, but also by a high level of endemism, likely to be determined by local stochastic processes such as drift and dispersal limitation at short distances. Despite the high site specificity in communities, they are dominated everywhere by a core set of lineages with little preferences toward habitat conditions or host phylogeny. Our results suggest a convergent evolution across phylogenetically distant lineages toward the root‐colonizing habit, and a functional redundancy in strategies for habitat colonization and host interaction. Further efforts are needed to integrate functional trait composition in future community ecology studies of root‐colonizing fungi.
Summary
Root endophytic fungi are found in a great variety of plants and ecosystems, but the ecological drivers of their biogeographic distribution are poorly understood. Here, we investigate the ...occurrence of root endophytes in the non‐mycorrhizal plant genus Microthlaspi, and the effect of environmental factors and geographic distance in structuring their communities at a continental scale. We sampled 52 plant populations across the northern Mediterranean and central Europe and used a cultivation approach to study their endophytic communities. Cultivation of roots yielded 2601 isolates, which were grouped into 296 operational taxonomic units (OTUs) by internal transcribed spacer sequencing of 1998 representative colonies. Climatic and spatial factors were the best descriptors of the structure of endophytic communities, outweighing soil characteristics, host genotype and geographical distance. OTU richness was negatively affected by precipitation, and the composition of communities followed latitudinal gradients of precipitation and temperature. Only six widespread OTUs belonging to the orders Pleosporales, Hypocreales and Helotiales represented about 50% of all isolates. Assessments of their individual distribution revealed particular ecological preferences or a cosmopolitan occurrence. Our findings support a strong influence of the local environment in determining root endophytic communities, and show a different niche occupancy by individual endophytes.
Summary
Background
Xanthomonas campestris pv. campestris (Xcc) (Pammel) Dowson is a Gram‐negative bacterium that causes black rot, the most important disease of vegetable brassica crops worldwide. ...Intensive molecular investigation of Xcc is gaining momentum and several whole genome sequences are available.
Taxonomy
Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Order Xanthomonadales; Family Xanthomonadacea; Genus Xanthomonas; Species X. campestris.
Host range and symptoms
Xcc can cause disease in a large number of species of Brassicaceae (ex‐Cruciferae), including economically important vegetable Brassica crops and a number of other cruciferous crops, ornamentals and weeds, including the model plant Arabidopsis thaliana. Black rot is a systemic vascular disease. Typical disease symptoms include V‐shaped yellow lesions starting from the leaf margins and blackening of the veins.
Race structure, pathogenesis and epidemiology
Collections of Xcc isolates have been differentiated into physiological races based on the response of several brassica species lines. Black rot is a seed‐borne disease. The disease is favoured by warm, humid conditions and can spread rapidly from rain dispersal and irrigation water.
Disease control
The control of black rot is difficult and relies on the use of pathogen‐free planting material and the elimination of other potential inoculum sources (infected crop debris and cruciferous weeds). Major gene resistance is very rare in B. oleracea (brassica C genome). Resistance is more readily available in other species, including potentially useful sources of broad‐spectrum resistance in B. rapa and B. carinata (A and BC genomes, respectively) and in the wild relative A. thaliana.
Genome
The reference genomes of three isolates have been released. The genome consists of a single chromosome of approximately 5 100 000 bp, with a GC content of approximately 65% and an average predicted number of coding DNA sequences (CDS) of 4308.
Important genes identified
Three different secretion systems have been identified and studied in Xcc. The gene clusters xps and xcs encode a type II secretion system and xps genes have been linked to pathogenicity. The role of the type IV secretion system in pathogenicity is still uncertain. The hrp gene cluster encodes a type III secretion system that is associated with pathogenicity. An inventory of candidate effector genes has been assembled based on homology with known effectors. A range of other genes have been associated with virulence and pathogenicity, including the rpf, gum and wxc genes involved in the regulation of the synthesis of extracellular degrading enzymes, xanthan gum and lipopolysaccharides.
Useful website
http://www.xanthomonas.org/
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