Non-invasive microelectrode potassium flux measurements as a potential tool for early recognition of virus–host compatibility in plants

Diseases caused by plant viruses are widespread, resulting in severe economic losses worldwide. Understanding the cellular basis of defense responses and developing efficient diagnostic tools for early recognition of host specificity to viral infection is, therefore, of great importance. In this work, non-invasive ion selective microelectrodes (the MIFE technique) were used to measure net ion fluxes in mesophyll tissue of host (potato, tomato, tobacco) and non-host (sugar beet and periwinkle) plants in response to infection with Potato virus X (PVX). These results were complemented by FLIM (Fluorescence Lifetime Imaging) measurements of PVX-induced changes in intracellular Ca²⁺ concentrations. Our results demonstrate that, unlike in other plant–pathogen interactions, Ca²⁺ signaling appears to be non-essential in recognition of the early stages of viral infection. Instead, we observed significant changes in K⁺ fluxes as early as 10 min after inoculation. Results of pharmacological experiments and membrane potential measurements pointed out that a significant part of these fluxes may be mediated by depolarization-activated outward-rectifying K⁺ channels. This may suggest that viral infections trigger a different mechanism of plant defense signaling as compared to signals derived from other microbial pathogens; hence, altered Ca²⁺ fluxes across the plasma membrane may not be a prerequisite for all elicitor-activated defense reactions. Clearly pronounced host specificity in K⁺ flux responses suggests that the MIFE technique can be effectively used as a screening tool for the early diagnostics of virus–host compatibility.     

Autophagy—from molecular mechanisms to clinical relevance

Autophagy is a lysosomal degradation pathway of eukaryotic cells that is highly conserved from yeast to mammals. During this process, cooperating protein complexes are recruited in a hierarchic order to the phagophore assembly site (PAS) to mediate the elongation and closure of double-membrane vesicles called autophagosomes, which sequester cytosolic components and deliver their content to the endolysosomal system for degradation. As a major cytoprotective mechanism, autophagy plays a key role in the stress response against nutrient starvation, hypoxia, and infections. Although numerous studies reported that impaired function of core autophagy proteins also contributes to the development and progression of various human diseases such as neurodegenerative disorders, cardiovascular and muscle diseases, infections, and different types of cancer, the function of this process in human diseases remains unclear. Evidence often suggests a controversial role for autophagy in the pathomechanisms of these severe disorders. Here, we provide an overview of the molecular mechanisms of autophagy and summarize the recent advances on its function in human health and disease.     

Cell wall integrity maintenance in plants: Lessons to be learned from yeast?

The plant cell wall is involved in different biological processes like cell morphogenesis and response to biotic/abiotic stress. Functional integrity of the wall is apparently being maintained during these processes by changing structure/composition and coordinating cell wall with cellular metabolism. In S.cerevisiae a well-characterized mechanism exists that is maintaining functional integrity of yeast the cell wall during similar processes. During the last years it has become obvious that plants have evolved a mechanism to monitor and maintain functional integrity of their cell walls. However, our understanding of the mechanism is rather limited. The available evidence suggests that similar signaling cascades may be involved and particular protein activities may be conserved between plants and yeast. Here we review the available evidence briefly and highlight similarities between yeast and plants that could help us to understand the mode of action of the signaling cascades maintaining plant cell wall integrity.     

Autophagy as a mechanism of antiviral defense at the maternal–fetal interface

Mechanisms to protect against viral infections are crucial during pregnancy as maternal-fetal transmission can have serious pathological outcomes, including fetal infection and its sequelae, such as growth restriction, birth defects, and/or fetal death. The trophoblast forms the interface between the feto-placental unit and the maternal blood, and is therefore a critical physical and immunological barrier to restrict the spread of pathogens into the fetal microenvironment. Recently, we found that primary human placental trophoblast (PHT) cells are highly resistant to infection by diverse viruses. In this study, we also found that conditioned medium from PHT cell cultures transferred viral resistance to nonplacental recipient cells, suggesting that a component secreted by trophoblasts and present within the conditioned medium is responsible for this antiviral effect. We found that specific miRNAs from a unique primate- and placental-specific locus—the C19MC (chromosome 19 miRNA cluster)—are packaged within exosomes produced by PHT cells and confer viral resistance in nonplacental recipient cells. In addition to conveying viral resistance, we found that PHT-derived exosomes and select miRNA members of the C19MC family strongly induce autophagy, which is involved in recipient cell viral resistance. Our findings establish an exciting and novel mechanism by which placental trophoblasts exploit exosome-dependent transfer of placental-specific miRNAs to influence autophagic induction and antiviral immunity at the maternal–fetal interface.     

Double fertilization in flowering plants: 1898–2008

The present article gives a brief survey of results of studies in the area of plant embryology directly associated with the discovery made by S.G. Navashin in 1898 of double fertilization in vivo and in vitro. These studies utilized methods of electronic and fluorescence microscopy, cytophotometry, and cultures of isolated ovules, sperm, and the embryo sac central cell. Questions related to the origin of the female gametophyte of flowering plants, double fertilization, and the endosperm are considered. It is emphasized that progress in this field is associated chiefly with the study of molecular processes that regulate the development and functioning of the female gametophyte and the sporophyte on early stages of ontogenesis.     

PKA-dependent dynein switching from lysosomes to adenovirus: A novel form of host–virus competition

Cytoplasmic dynein is responsible for transport of several viruses to the nucleus. Adenovirus recruits dynein directly. Transport depends on virus-induced activation of protein kinase A (PKA) and other cellular protein kinases, whose roles in infection are poorly understood. We find that PKA phosphorylates cytoplasmic dynein at a novel site in light intermediate chain 1 (LIC1) that is essential for dynein binding to the hexon capsid subunit and for virus motility. Surprisingly, the same LIC1 modification induces a slow, but specific, dispersal of lysosomes (lyso)/late endosomes (LEs) that is mediated by inhibition of a newly identified LIC1 interaction with the RILP (Rab7-interacting lysosomal protein). These results identify an organelle-specific dynein regulatory modification that adenovirus uses for its own transport. PKA-mediated LIC1 phosphorylation causes only partial lyso/LE dispersal, suggesting a role for additional, parallel mechanisms for dynein recruitment to lyso/LEs. This arrangement provides a novel means to fine tune transport of these organelles in response to infection as well as to developmental and physiological cues.     

Mutualism and manipulation in Hadza–honeyguide interactions

We investigated the ecology and evolution of interspecific cooperation between the Greater Honeyguide bird, Indicator indicator, and human hunter-gatherers, the Hadza of northern Tanzania. We found that honeyguides increased the Hadza's rate of finding bee nests by 560%, and that the birds led men to significantly higher yielding nests than those found without honeyguides. We estimate that 8–10% of the Hadza's total diet was acquired with the help of honeyguides. Contrary to most depictions of the human-honeyguide relationship, the Hadza did not actively repay honeyguides, but instead, hid, buried, and burned honeycomb, with the intent of keeping the bird hungry and thus more likely to guide again. Such manipulative behavior attests to the importance of social intelligence in hunter-gatherer foraging strategies. We present an evolutionary model for human-honeyguide interactions guided by the behavioral ecology of bees, non-human primates, and hunter-gatherers.     

Buzz in Paris: flower production and plant–pollinator interactions in plants from contrasted urban and rural origins

Urbanisation, associated with habitat fragmentation, affects pollinator communities and insect foraging behaviour. These biotic changes are likely to select for modified traits in insect-pollinated plants from urban populations compared to rural populations. To test this hypothesis, we conducted an experiment involving four plant species commonly found in both urban and rural landscapes of the Île-de-France region (France): Cymbalaria muralis, Geranium robertianum, Geum urbanum and Prunella vulgaris. The four species were grown in four urban and four rural experimental sites in 2015. For each species and each experimental site, plants were grown from seeds collected in five urban and five rural locations. During flowering, we observed flower production and insect–flower interactions during 14 weeks and tested for the effects of experimental site location and plant origin on flower production and on the number of floral visits. The study species had various flower morphology and hence were visited by different floral visitors. The effect of experimental sites and seed origin also varied among study species. We found that (1) insect visits on P. vulgaris were more frequent in rural than in urban sites; (2) for C. muralis, the slope relating the number of pollinator visits to the number of flowers per individual was steeper in urban versus rural sites, suggesting a greater benefit in allocating resources to flower production in urban conditions; (3) as a likely consequence, C. muralis tended to produce more flowers in plants from urban versus rural origin.     

Conundrums of competitive ability in plants: what to measure?

A survey of recent literature indicates that competitive ability in plants has been measured, in most studies, only in terms of the relative intensity of size suppression experienced by competitors within one growing season. Far fewer studies have recorded relative success in terms of survival and even fewer studies have recorded fecundity under competition. Differences in size suppression are usually assumed to reflect differences in relative abilities to deny resources to competitors. However, most previous studies have failed to control or account for other sources of variation in the size suppression that plants experience under competition, i.e. variation between mixtures in the resource supply/demand ratio (approach to carrying capacity), or variation in the degree of niche overlap between competitors, or variation in the intensity of concurrent facilitative interactions between competitors. For future studies, much greater caution is required in recognizing these inherent limitations of traditional measures of competitive ability and, hence, guarding against unfounded conclusions or predictions about potential for competitive success that are based on these measures. There is also a significant challenge for future studies to adopt empirical approaches for minimizing these limitations. Some initial recommendations are considered here based on an emerging view of competitive ability measured in terms of traits associated with all three conventional components of Darwinian fitness, i.e. not just growth (plant size) but also survival and fecundity allocation (offspring production per unit plant size per unit time). According to this model, differences in competitive ability imply differences in the ability, despite intense competition (i.e. low resource supply/demand ratio), to recruit offspring into the next generation and thereby limit offspring recruitment by other plants. The important traits of competitive ability, therefore, are not only those that allow a plant to deny resources to competitors, suppress their sizes and hence, maximize the plant's own size, but also those traits that allow the plant to withstand suppression from competition enough to persist, both as an individual (through survival) and across generations (through descendants).     

Self–other control processes in social cognition: from imitation to empathy

We review the evidence that an ability to achieve a precise balance between representing the self and representing other people is crucial in social interaction. This ability is required for imitation, perspective-taking, theory of mind and empathy; and disruption to this ability may contribute to the symptoms of clinical and sub-clinical conditions, including autism spectrum disorder and mirror-touch synaesthesia. Moving beyond correlational approaches, a recent intervention study demonstrated that training participants to control representations of the self and others improves their ability to control imitative behaviour, and to take another''s visual perspective. However, it is unclear whether these effects apply to other areas of social interaction, such as the ability to empathize with others. We report original data showing that participants trained to increase self–other control in the motor domain demonstrated increased empathic corticospinal responses (Experiment 1) and self-reported empathy (Experiment 2), as well as an increased ability to control imitation. These results suggest that the ability to control self and other representations contributes to empathy as well as to other types of social interaction.     

Responses of plants to changes in Qinghai–Tibetan Plateau and glaciations: Evidence from phylogeography of a Sibiraea (Rosaceae) complex

The genetic structure and phylogeographical history of the alpine shrubs Sibiraea angustata (Rosaceae) and Sibiraea laevigata from the Qinghai–Tibetan Plateau (QTP) were investigated to identify alpine plant responses to changes in the QTP and glaciations. Fifty-five populations were analyzed using four chloroplast DNA (cpDNA) regions and (nuclear ribosomal internal transcribed spacer) nrITS sequence data. In all, 21 cpDNA haplotypes and 13 nrITS sequence types were detected. Analyses of the genetic diversity and phylogenetic relationships detected two rarely reported glacial refugia. One was the Yushu–Nangqian area, and the other consisted of the area from the Songpan Plateau to the southeastern margin of the QTP. Sibiraea species populations experienced divergent evolution and founder effects when they recolonized the QTP platform and adjacent high-altitude regions following glaciations. The divergence times of the main lineages and haplotypes were in the range of 1.60–2.58 Ma. The population size of Sibiraea species in the QTP decreased approximately 23-fold during the last 0.12 Ma, indicating that Sibiraea species were significantly affected by environmental changes in the QTP. Therefore, the rapid uplift of the QTP and subsequent glaciations likely played an important role in driving genetic divergence and population size changes of Sibiraea species in the QTP.     

Nocturnal energy demand in plants: Insights from studying mutants impaired in β-oxidation

All photosynthetic organisms face the difficulty of maintaining cellular metabolism in the absence of photosynthetic active radiation during the night. Although many consuming metabolic pathways (e.g., fatty acid synthesis) are only active in the light, plant cells still require basic levels of metabolic energy and reductive power during the night for sustained growth and development.Key words: PXA1, comatose, β-oxidation, fatty acids, starch, imaging PAM, extended darkness     

B chromosomes in plants: escapees from the A chromosome genome?

B chromosomes are dispensable elements that do not recombine with the A chromosomes of the regular complement and that follow their own evolutionary track. In some cases, they are known to be nuclear parasites with autonomous modes of inheritance, exploiting "drive" to ensure their survival in populations. Their "selfishness" brings them into conflict with their host nuclear genome and generates a host-parasite relationship, with anti-B-chromosome genes working to ameliorate the worst of their excesses in depriving their hosts of genetic resources. Molecular studies are homing in on their sequence organization to give us an insight into the origin and evolution of these enigmatic chromosomes, which are, with rare exceptions, without active genes.