Genetic complementation analysis of the Agrobacterium tumefaciens virB operon: virB2 through virB11 are essential virulence genes.

The Agrobacterium tumefaciens virB gene products are proposed to assemble into a transport system capable of exporting complexes of DNA and protein across the bacterial envelope en route to plant cells. Nonpolar null mutations were constructed in each of the 11 virB genes of the A. tumefaciens pTiA6NC plasmid. In tumorigenicity assays, delta virB1 mutants exhibited severely attenuated virulence and delta virB2 through delta virB11 mutants exhibited avirulence. NdeI restriction sites introduced at the predicted translational start sites of the virB genes were used to subclone each of the virB genes downstream of the lacZ or virB promoter on broad-host-range plasmids. virB gene expression plasmids were used to define promoter and general sequence requirements for genetic complementation of the deletion mutations. Whereas virB1 and virB2 complemented delta virB1 and delta virB2, respectively, only when expressed in trans from the virB promoter, virB3 through virB11 complemented the corresponding deletion mutations when expressed in trans from either the lacZ or virB promoter. Several virB genes required additional upstream or downstream sequences for complementation: (i) virB2 complemented the delta virB2 mutation only when the complementing plasmid coexpressed virB1 and virB2, (ii) virB6 and virB9 complemented the delta virB6 and delta virB9 mutations only when the complementing plasmids carried at most 55 and 230 bp of sequences residing 5' of these genes, respectively, and (iii) virB7 and virB8 complemented the delta virB7 and delta virB8 mutations only when the complementing plasmid coexpressed virB7 and virB8. These studies established that virB1 is an accessory virulence determinant and virB2 through virB11 are absolutely essential for the A. tumefaciens infection process.     

Status,trends and drivers of kelp forests in Europe: an expert assessment

A comprehensive expert consultation was conducted in order to assess the status, trends and the most important drivers of change in the abundance and geographical distribution of kelp forests in European waters. This consultation included an on-line questionnaire, results from a workshop and data provided by a selected group of experts working on kelp forest mapping and eco-evolutionary research. Differences in status and trends according to geographical areas, species identity and small-scale variations within the same habitat where shown by assembling and mapping kelp distribution and trend data. Significant data gaps for some geographical regions, like the Mediterranean and the southern Iberian Peninsula, were also identified. The data used for this study confirmed a general trend with decreasing abundance of some native kelp species at their southern distributional range limits and increasing abundance in other parts of their distribution (Saccharina latissima and Saccorhiza polyschides). The expansion of the introduced species Undaria pinnatifida was also registered. Drivers of observed changes in kelp forests distribution and abundance were assessed using experts’ opinions. Multiple possible drivers were identified, including global warming, sea urchin grazing, harvesting, pollution and fishing pressure, and their impact varied between geographical areas. Overall, the results highlight major threats for these ecosystems but also opportunities for conservation. Major requirements to ensure adequate protection of coastal kelp ecosystems along European coastlines are discussed, based on the local to regional gaps detected in the study.     

Along the speciation continuum: Quantifying intrinsic and extrinsic isolating barriers across five million years of evolutionary divergence in California jewelflowers

Understanding the relative roles of intrinsic and extrinsic reproductive barriers, and their interplay within the geographic context of diverging taxa, remains an outstanding challenge in the study of speciation. We conducted a comparative analysis of reproductive isolation in California Jewelflowers (Streptanthus, s.l., Brassicaceae) by quantifying potential barriers to gene flow at multiple life history stages in 39 species pairs spanning five million years of evolutionary divergence. We quantified nine potential pre‐ and postzygotic barriers and explored patterns of reproductive isolation in relation to genetic distance. Intrinsic postzygotic isolation was initially weak, increased at intermediate genetic distances, and reached a threshold characterized by complete genetic incompatibility. Climatic niche differences were strong at shallow genetic distances, and species pairs with overlapping ranges showed slight but appreciable phenological isolation, highlighting the potential for ecological barriers to contribute to speciation. Geographic analyses suggest that speciation is not regionally allopatric in the California Jewelflowers, as recently diverged taxa occur in relatively close proximity and display substantial range overlap. Young pairs are characterized by incomplete intrinsic postzygotic isolation, suggesting that extrinsic barriers or fine‐scale spatial segregation are more important early in the divergence process than genetic incompatibilities.     

Predation potential of <Emphasis Type="Italic">Rhynocoris marginatus</Emphasis> (Hemiptera: Reduviidae) against three mealybug species of agricultural importance

The predation potential of a generalist predator Rhynocoris marginatus (Fab.) (Hemiptera: Reduviidae) against three important mealybug pests of cotton, Phenacoccus solenopsis Tinsley, Maconellicoccus hirsutus Green, and Coccidohystrix insolita Green (Hemiptera: Pseudococcidae) was evaluated under laboratory conditions. The specific objective of the study was to determine the prey capturing time, prey handling time, and prey preference among the three mealybug species for different developmental stages of R. marginatus. The number of prey consumed/predator/24 h by R. marginatus was dependent on the mealybug species and the predator developmental stage. Rhynocoris marginatus showed a decrease in prey capturing time and handling time as the predator grew older. After evaluating the prey stage preference, results indicated that the developmental stages of R. marginatus preferred adult mealybugs over the younger stages. In a choice-test bioassay including the three mealybug species, no significant difference in prey species selection was observed for the various R. marginatus developmental stages. However, the mortality of P. solenopsis was observed to be highest among the mealybugs, followed by M. hirsutus and C. insolita. This supports the idea that R. marginatus can be effectively utilized for the management of one of the most destructive mealybug pests of cotton, P. solenopsis. Results from this study are important for the development of a knowledge-based management program for cotton agroecosystems affected by various mealybug pests.     

Body size shapes inter‐specific migratory behaviour: evidence from individual tracks of long‐distance migratory shorebirds

Migration is a common phenomenon across many animal taxa. Understanding how migration scales with body size across species is fundamental in the development of migration theory and in making size‐related predictions. Although aerodynamic theory and ecophysiological scaling laws have assisted greatly in generating such predictions, their verifications have been limited by a lack of empirical data across a range of body sizes. The recent development of ultra‐light tracking devices and its rapid application to migration now allows us to put theory to the test. We used tracking data of seven closely related migratory sandpiper species (family Scolopacidae) along the East Asian‐Australasian Flyway to compare their migratory behaviour when migrating towards the breeding grounds as a function of size (50–750 g). We found a marked decline in migration speed (migration distance divided by total migration duration, including time at stopover sites and in flight) with size. Departure date from the non‐breeding (i.e. wintering) ground and arrival date at the breeding ground also scaled negatively with size. Total migration duration, migration distance, total staging duration (the number of days staying at stopover sites plus days preparing, i.e. fuelling, prior to initial migration) and step length (distance covered within one migratory leg) were not significantly related with size. Correction for phylogeny showed consistent results for all variables. Besides improving our fundamental understanding of inter‐specific variation in migration behaviours, the finding of a clear scaling with size in migration speed and migration timing highlight differential size related capabilities and constraints of migrants. Migratory birds, including sandpipers, are declining on a global scale and particularly along the East Asian‐Australasian Flyway. This notion of size‐dependency in migratory traits may have a bearing on their vulnerability to specific environmental disturbances along their flyways.     

Type IV secretion in Gram‐negative and Gram‐positive bacteria

Type IV secretion systems (T4SSs) are versatile multiprotein nanomachines spanning the entire cell envelope in Gram‐negative and Gram‐positive bacteria. They play important roles through the contact‐dependent secretion of effector molecules into eukaryotic hosts and conjugative transfer of mobile DNA elements as well as contact‐independent exchange of DNA with the extracellular milieu. In the last few years, many details on the molecular mechanisms of T4SSs have been elucidated. Exciting structures of T4SS complexes from Escherichia coli plasmids R388 and pKM101, Helicobacter pylori and Legionella pneumophila have been solved. The structure of the F‐pilus was also reported and surprisingly revealed a filament composed of pilin subunits in 1:1 stoichiometry with phospholipid molecules. Many new T4SSs have been identified and characterized, underscoring the structural and functional diversity of this secretion superfamily. Complex regulatory circuits also have been shown to control T4SS machine production in response to host cell physiological status or a quorum of bacterial recipient cells in the vicinity. Here, we summarize recent advances in our knowledge of ‘paradigmatic’ and emerging systems, and further explore how new basic insights are aiding in the design of strategies aimed at suppressing T4SS functions in bacterial infections and spread of antimicrobial resistances.     

Single and multiple phenotype QTL analyses of downy mildew resistance in interspecific grapevines

Key message

Downy mildew resistance across days post-inoculation, experiments, and years in two interspecific grapevine F₁ families was investigated using linear mixed models and Bayesian networks, and five new QTL were identified.

Abstract

Breeding grapevines for downy mildew disease resistance has traditionally relied on qualitative gene resistance, which can be overcome by pathogen evolution. Analyzing two interspecific F₁ families, both having ancestry derived from Vitis vinifera and wild North American Vitis species, across 2 years and multiple experiments, we found multiple loci associated with downy mildew sporulation and hypersensitive response in both families using a single phenotype model. The loci explained between 7 and 17% of the variance for either phenotype, suggesting a complex genetic architecture for these traits in the two families studied. For two loci, we used RNA-Seq to detect differentially transcribed genes and found that the candidate genes at these loci were likely not NBS-LRR genes. Additionally, using a multiple phenotype Bayesian network analysis, we found effects between the leaf trichome density, hypersensitive response, and sporulation phenotypes. Moderate–high heritabilities were found for all three phenotypes, suggesting that selection for downy mildew resistance is an achievable goal by breeding for either physical- or non-physical-based resistance mechanisms, with the combination of the two possibly providing durable resistance.

     

Multiple non-catalytic ADAMs are novel integrin α4 ligands

The ADAM (a disintegrin and metalloprotease) protein family uniquely exhibits both catalytic and adhesive properties. In the well-defined process of ectodomain shedding, ADAMs transform latent, cell-bound substrates into soluble, biologically active derivatives to regulate a spectrum of normal and pathological processes. In contrast, the integrin ligand properties of ADAMs are not fully understood. Emerging models posit that ADAM–integrin interactions regulate shedding activity by localizing or sequestering the ADAM sheddase. Interestingly, 8 of the 21 human ADAMs are predicted to be catalytically inactive. Unlike their catalytically active counterparts, integrin recognition of these “dead” enzymes has not been largely reported. The present study delineates the integrin ligand properties of a group of non-catalytic ADAMs. Here we report that human ADAM11, ADAM23, and ADAM29 selectively support integrin α4-dependent cell adhesion. This is the first demonstration that the disintegrin-like domains of multiple catalytically inactive ADAMs are ligands for a select subset of integrin receptors that also recognize catalytically active ADAMs.