Pollen S–locus F–box proteins of Petunia involved in S–RNase‐based self‐incompatibility are themselves subject to ubiquitin‐mediated degradation

Many flowering plants show self‐incompatibility, an intra‐specific reproductive barrier by which pistils reject self‐pollen to prevent inbreeding and accept non‐self pollen to promote out‐crossing. In Petunia, the polymorphic S–locus determines self/non‐self recognition. The locus contains a gene encoding an S–RNase, which controls pistil specificity, and multiple S‐locus F‐box (SLF) genes that collectively control pollen specificity. Each SLF is a component of an SCF (Skp1/Cullin/F‐box) complex that is responsible for mediating degradation of non‐self S‐RNase(s), with which the SLF interacts, via the ubiquitin–26S proteasome pathway. A complete set of SLFs is required to detoxify all non‐self S‐RNases to allow cross‐compatible pollination. Here, we show that SLF1 of Petunia inflata is itself subject to degradation via the ubiquitin–26S proteasome pathway, and identify an 18 amino acid sequence in the C‐terminal region of S₂‐SLF1 (SLF1 of S₂ haplotype) that contains a degradation motif. Seven of the 18 amino acids are conserved among all 17 SLF proteins of S₂ haplotype and S₃ haplotype involved in pollen specificity, suggesting that all SLF proteins are probably subject to similar degradation. Deleting the 18 amino acid sequence from S₂‐SLF1 stabilized the protein but abolished its function in self‐incompatibility, suggesting that dynamic cycling of SLF proteins is an integral part of their function in self‐incompatibility.     

Antiviral Triketone‐Phloroglucinol‐Monoterpene Adducts from Callistemon rigidus

Callistrilones F – K ( 1 – 6 ), six new triketone‐phloroglucinol‐monoterpene hybrids were isolated from the twigs and leaves of Callistemon rigidus. Their structures with absolute configurations were established by a combination analysis of NMR spectra, X‐ray diffraction, and electronic circular dichroism (ECD) calculations. Compounds 3 and 4 exhibited moderate inhibitory activities against herpes simplex virus (HSV‐1) with IC₅₀ values of 10.00 ± 2.50 and 12.50 ± 1.30 μm , respectively.     

Multiple host‐cell recombination pathways act in Agrobacterium‐mediated transformation of plant cells

Using floral‐dip, tumorigenesis and root callus transformation assays of both germline and somatic cells, we present here results implicating the four major non‐homologous and homologous recombination pathways in Agrobacterium‐mediated transformation of Arabidopsis thaliana. All four single mutant lines showed similar mild reductions in transformability, but knocking out three of four pathways severely compromised Agrobacterium‐mediated transformation. Although integration of T–DNA into the plant genome is severely compromised in the absence of known DNA double‐strand break repair pathways, it does still occur, suggesting the existence of other pathways involved in T–DNA integration. Our results highlight the functional redundancy of the four major plant recombination pathways in transformation, and provide an explanation for the lack of strong effects observed in previous studies on the roles of plant recombination functions in transformation.     

Adaptive divergence along environmental gradients in a climate‐change‐sensitive mammal

In the face of predicted climate change, a broader understanding of biotic responses to varying environments has become increasingly important within the context of biodiversity conservation. Local adaptation is one potential option, yet remarkably few studies have harnessed genomic tools to evaluate the efficacy of this response within natural populations. Here, we show evidence of selection driving divergence of a climate‐change‐sensitive mammal, the American pika (Ochotona princeps), distributed along elevation gradients at its northern range margin in the Coast Mountains of British Columbia (BC), Canada. We employed amplified‐fragment‐length‐polymorphism‐based genomic scans to conduct genomewide searches for candidate loci among populations inhabiting varying environments from sea level to 1500 m. Using several independent approaches to outlier locus detection, we identified 68 candidate loci putatively under selection (out of a total 1509 screened), 15 of which displayed significant associations with environmental variables including annual precipitation and maximum summer temperature. These candidate loci may represent important targets for predicting pika responses to climate change and informing novel approaches to wildlife conservation in a changing world.     

Sex‐skewed trophic impacts in ephemeral wetlands

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Hit‐and‐run trophallaxis of small hive beetles

Some parasites of social insects are able to exploit the exchange of food between nestmates via trophallaxis, because they are chemically disguised as nestmates. However, a few parasites succeed in trophallactic solicitation although they are attacked by workers. The underlying mechanisms are not well understood. The small hive beetle (=SHB), Aethina tumida, is such a parasite of honey bee, Apis mellifera, colonies and is able to induce trophallaxis. Here, we investigate whether SHB trophallactic solicitation is innate and affected by sex and experience. We quantified characteristics of the trophallactic solicitation in SHBs from laboratory‐reared individuals that were either bee‐naïve or had 5 days experience. The data clearly show that SHB trophallactic solicitation is innate and further suggest that it can be influenced by both experience and sex. Inexperienced SHB males begged more often than any of the other groups had longer breaks than their experienced counterparts and a longer soliciting duration than both experienced SHB males and females, suggesting that they start rather slowly and gain more from experience. Successful experienced females and males were not significantly different from each other in relation to successful trophallactic interactions, but had a significantly shorter soliciting duration compared to all other groups, except successful inexperienced females. Trophallactic solicitation success, feeding duration and begging duration were not significantly affected by either SHB sex or experience, supporting the notion that these behaviors are important for survival in host colonies. Overall, success seems to be governed by quality rather than quantity of interactions, thereby probably limiting both SHB energy investment and chance of injury (<1%). Trophallactic solicitation by SHBs is a singular example for an alternative strategy to exploit insect societies without requiring chemical disguise. Hit‐and‐run trophallaxis is an attractive test system to get an insight into trophallaxis in the social insects.     

Tracking changes in life‐history traits related to unnecessary virulence in a plant‐parasitic nematode

Evaluating trade‐offs in life‐history traits of plant pathogens is essential to understand the evolution and epidemiology of diseases. In particular, virulence costs when the corresponding host resistance gene is lacking play a major role in the adaptive biology of pathogens and contribute to the maintenance of their genetic diversity. Here, we investigated whether life‐history traits directly linked to the establishment of plant–nematode interactions, that is, ability to locate and move toward the roots of the host plant, and to invade roots and develop into mature females, are affected in Meloidogyne incognita lines virulent against the tomato Mi‐1.2 resistance gene. Virulent and avirulent near‐isogenic lines only differing in their capacity to reproduce or not on resistant tomatoes were compared in single inoculation or pairwise competition experiments. Data highlighted (1) a global lack of trade‐off in traits associated with unnecessary virulence with respect to the nematode ability to successfully infest plant roots and (2) variability in these traits when the genetic background of the nematode is considered irrespective of its (a)virulence status. These data suggest that the variation detected here is independent from the adaptation of M. incognita to host resistance, but rather reflects some genetic polymorphism in this asexual organism.     

A life‐cycle approach to species barriers

What maintains reproductive barriers between closely related species is, of course, of fundamental interest to a closer understanding of the mechanisms that generate new biodiversity. One important dichotomy is to separate barriers evolved from divergent selection over environmental gradients (extrinsic barriers) from barriers caused by incompatibilities between different genetic arrangements that may have evolved in isolation (intrinsic barriers). This dichotomy also reflects an important applied consequence. As the extrinsic barriers are associated with specific environmental contexts, they may be partly or completely erased if the environment changes. In contrast, intrinsic barriers are inert to the environmental context and resistant to environmental changes. From a conservation biology perspective, it may thus be important to be able to separate extrinsic and intrinsic species barriers, but this may in many organisms be a complex matter. In this issue of Molecular Ecology, Montecinos et al. ( 2017 ) found a tractable approach that works for species with life cycles that include two reproductive but ecologically similar generations, one haploid and the other diploid. What they demonstrate is that using a life‐cycle approach offers a unique possibility to separate between prezygotic and postzygotic barriers. Indeed, in the case of an isomorphic life cycle, there is even a possibility to suggest whether postzygotic barriers are more likely to be intrinsic or extrinsic. In this way, their approach may be useful both to increase our understanding of the basic mechanisms of speciation and to single out when species barriers will better resist environmental changes.     

Species‐ and site‐specific impacts of an invasive herbivore on tree survival in mixed forests

Invasive herbivores are often managed to limit their negative impact on plant populations, but herbivore density – plant damage relationships are notoriously spatially and temporally variable. Site and species characteristics (both plant and herbivore) must be considered when assessing the potential for herbivore damage, making it difficult to set thresholds for efficient management. Using the invasive brushtail possum Trichosurus vulpecula in New Zealand as a case study, we parameterized a generic model to predict annual probability of browse‐induced mortality of five tree species at 12 sites. We compared predicted and observed tree mortality for each species + site combination to establish herbivore abundance – tree mortality thresholds for each site on a single and combined tree species basis. Model results indicated it is likely that possum browse was the primary cause of all tree mortality at nine of the 12 species‐site combinations, allowing us to estimate site‐specific thresholds below which possum population numbers should be reduced and maintained to keep tree mortality under a predetermined level, for example 0.5% per year. The browse model can be used to set site‐ and species‐specific management action thresholds, and can be adapted easily for other plant or herbivore species. Results for multiple plant or herbivore species at a single site can be combined to create conservative, site‐wide management strategies, and used to: determine which sites will be affected most by changes in herbivore abundance; quantify thresholds for herbivore management; and justify expenditure on herbivore control.     

Landowners’ perspectives of black‐backed jackals (Canis mesomelas) on farmlands in KwaZulu‐Natal,South Africa

Despite continued efforts to eradicate black‐backed jackals (Canis mesomelas), they are considered an abundant mesopredator on agricultural land across South Africa, resulting in ongoing human–wildlife conflict and concern for farmers and wildlife managers. We conducted a questionnaire survey and semi‐formal interviews with farmers throughout KwaZulu‐Natal, examining farmers’ livestock husbandry, land‐use changes and perspectives towards jackals as a perceived threat to livestock. Many (75%) respondents acknowledged expanding agricultural activities on their farmlands since the onset of their farming careers. However, the perception was that these changes placed little pressure on mesopredators as farmers reported frequent daily (25%) and weekly (31%) sightings of jackal, and regular predation on livestock (72%). Some landowners (31%) reported between one and five livestock losses annually and suggest that mitigation strategies to prevent livestock losses are in place. Farmers suggested the increasing intensity in agricultural practices provided a greater food source for jackals allowing them to thrive in expanding agricultural conditions and, in some circumstances, farmers admitted to possibly being a cause through poor disposal techniques for dead animals. Feedback from farmers emphasized the importance of having collaboration between farmers to control jackal predation and reduce human–wildlife conflict.     

Differences in Anti‐Herbivore Defenses in Non‐Myrmecophyte and Myrmecophyte Cecropia Trees

Little is known about antiherbivore defenses in non‐myrmecophyte Cecropia trees. We compare two non‐myrmecophyte Cecropia—Cecropia sciadophylla and Cecropia tacuna—with Cecropia membranacea, a myrmecophyte. High levels of chemical defenses in young leaves and physical toughness of mature leaves compensate for the absence of mutualistic ants in C. sciadophylla. Some C. tacuna trees produce trichilia and Müllerian bodies suggesting it has lost a mutualism with ants.     

Loss‐of‐function of ASPARTIC PEPTIDASE NODULE‐INDUCED 1 (APN1) in Lotus japonicus restricts efficient nitrogen‐fixing symbiosis with specific Mesorhizobium loti strains

The nitrogen‐fixing symbiosis of legumes and Rhizobium bacteria is established by complex interactions between the two symbiotic partners. Legume Fix^– mutants form apparently normal nodules with endosymbiotic rhizobia but fail to induce rhizobial nitrogen fixation. These mutants are useful for identifying the legume genes involved in the interactions essential for symbiotic nitrogen fixation. We describe here a Fix^– mutant of Lotus japonicus, apn1, which showed a very specific symbiotic phenotype. It formed ineffective nodules when inoculated with the Mesorhizobium loti strain TONO. In these nodules, infected cells disintegrated and successively became necrotic, indicating premature senescence typical of Fix^– mutants. However, it formed effective nodules when inoculated with the M. loti strain MAFF303099. Among nine different M. loti strains tested, four formed ineffective nodules and five formed effective nodules on apn1 roots. The identified causal gene, ASPARTIC PEPTIDASE NODULE‐INDUCED 1 (LjAPN1), encodes a nepenthesin‐type aspartic peptidase. The well characterized Arabidopsis aspartic peptidase CDR1 could complement the strain‐specific Fix^– phenotype of apn1. LjAPN1 is a typical late nodulin; its gene expression was exclusively induced during nodule development. LjAPN1 was most abundantly expressed in the infected cells in the nodules. Our findings indicate that LjAPN1 is required for the development and persistence of functional (nitrogen‐fixing) symbiosis in a rhizobial strain‐dependent manner, and thus determines compatibility between M. loti and L. japonicus at the level of nitrogen fixation.     

Geographic and host‐mediated population genetic structure in a cestode parasite of the three‐spined stickleback

Comparative studies of genetic diversity and population structure can shed light on the ecological and evolutionary factors that influence host–parasite interactions. Here we examined whether geography, time and genetic variation in Alaskan three‐spined stickleback (Gasterosteus aculeatus Linneaus) hosts shape the population genetic structure of the diphyllobothridean cestode parasite Schistocephalus solidus (Müller, 1776). Host lineages and haplotypes were identified by sequencing the mitochondrial cytochrome b gene, and host population structure was assessed by Bayesian clustering analysis of allelic variation at 11 microsatellite loci. Parasite population structure was characterized according to allelic variation at eight microsatellite loci. Mantel tests and canonical redundancy analysis were conducted to evaluate the proportion of parasite genetic variation attributable to time and geography vs. host lineage, haplotype, and genotypic cluster. Host and parasite population structure were largely discordant across the study area, probably reflecting differences in gene flow, environmental influences external to the host, and genomic admixture among host lineages. We found that geography explained the greatest proportion of parasite genetic variation, but that variation also reflects time, host lineage, and host haplotype. Associations with host haplotypes suggest that one parasite genotypic cluster exhibits a narrower host range, predominantly infecting the most common host haplotypes, whereas the other parasite cluster infects all haplotypes equally, including rare haplotypes. Although experimental infection trials might prove otherwise, distributional differences in hosts preferentially infected by S. solidus could underlie the observed pattern of population structure.     

Melatonin alleviates lipopolysaccharide‐compromised integrity of blood–brain barrier through activating AMP‐activated protein kinase in old mice

Blood–brain barrier (BBB) dysfunction is considered to be an early event in the pathogenesis of a variety of neurological diseases in old patients, and this could occur in old people even when facing common stress. However, the mechanism remains to be defined. In this study, we tested the hypothesis that decreased melatonin levels may account for the BBB disruption in old mice challenged with lipopolysaccharide (LPS), which mimicked the common stress of sepsis. Mice (24–28 months of age) received melatonin (10 mg kg^?1 day^?1, intraperitoneally, i.p.) or saline for one week before exposing to LPS (1 mg kg^?1, i.p.). Evan's blue dye (EB) and immunoglobulin G (IgG) leakage were used to assess BBB permeability. Immunostaining and Western blot were used to detect protein expression and distribution. Our results showed that LPS significantly increased BBB permeability in old mice accompanied by the degradation of tight junction proteins occludin and claudin‐5, suppressed AMP‐activated protein kinase (AMPK) activation, and elevated gp91^phox protein expression. Interestingly, administration of melatonin for one week significantly decreased LPS‐induced BBB disruption, AMPK suppression, and gp91^phox upregualtion. Moreover, activation of AMPK with metformin significantly inhibited LPS‐induced gp91^phox upregualtion in endothelial cells. Taken together, our findings demonstrate that melatonin alleviates LPS‐induced BBB disruption through activating AMPK and inhibiting gp91^phox upregulation in old mice.     

No evidence for MHC‐based mate choice in wild giant pandas

Major histocompatibility complex genes (MHC), a gene cluster that controls the immune response to parasites, are regarded as an important determinant of mate choice. However, MHC‐based mate choice studies are especially rare for endangered animals. The giant panda (Ailuropoda melanoleuca), a flagship species, has suffered habitat loss and fragmentation. We investigated the genetic variation of three MHC class II loci, including DRB1, DQA1, and DQA2, for 19 mating‐pairs and 11 parent‐pairs of wild giant pandas based on long‐term field behavior observations and genetic samples. We tested four hypotheses of mate choice based on this MHC variation. We found no supporting evidence for the MHC‐based heterosis, genetic diversity, genetic compatibility and “good gene” hypotheses. These results suggest that giant pandas may not use MHC‐based signals to select mating partners, probably because limited mating opportunities or female‐biased natal dispersal restricts selection for MHC‐based mate choice, acknowledging the caveat of the small sample size often encountered in endangered animal studies. Our study provides insight into the mate choice mechanisms of wild giant pandas and highlights the need to increase the connectivity and facilitate dispersal among fragmented populations and habitats.     

G protein‐coupled estrogen receptor‐mediated effects on cytosolic calcium and nanomechanics in brain microvascular endothelial cells

G protein‐coupled estrogen receptor (GPER) is a relatively recently identified non‐nuclear estrogen receptor, expressed in several tissues, including brain and blood vessels. The mechanisms elicited by GPER activation in brain microvascular endothelial cells are incompletely understood. The purpose of this work was to assess the effects of GPER activation on cytosolic Ca²⁺ concentration, [Ca²⁺]_i, nitric oxide production, membrane potential and cell nanomechanics in rat brain microvascular endothelial cells (RBMVEC). Extracellular but not intracellular administration of G‐1, a selective GPER agonist, or extracellular administration of 17‐β‐estradiol and tamoxifen, increased [Ca²⁺]_i in RBMVEC. The effect of G‐1 on [Ca²⁺]_i was abolished in Ca²⁺‐free saline or in the presence of a L‐type Ca²⁺ channel blocker. G‐1 increased nitric oxide production in RBMVEC; the effect was prevented by NG‐nitro‐l ‐arginine methyl ester. G‐1 elicited membrane hyperpolarization that was abolished by the antagonists of small and intermediate‐conductance Ca²⁺‐activated K⁺ channels, apamin, and charibdotoxin. GPER‐mediated responses were sensitive to G‐36, a GPER antagonist. In addition, atomic force microscopy studies revealed that G‐1 increased the modulus of elasticity, indicative of cytoskeletal changes and increase in RBMVEC stiffness. Our results unravel the mechanisms underlying GPER‐mediated effects in RBMVEC with implications for the effect of estrogen on cerebral microvasculature.