Lesion mimic mutants: keys for deciphering cell death and defense pathways in plants?

The identification of several lesion mimic mutants (LMM) that misregulate cell death constitutes a powerful tool to unravel programmed cell death (PCD) pathways in plants, particularly the hypersensitive response (HR), a form of PCD associated with resistance to pathogens. Recently, the characterization of novel LMM has enabled genes that might regulate cell death programmes to be identified as well as the dissection of defense signaling pathways and of crosstalk between multiple pathways in ways that might not be possible by studying the responses of wild-type plants to pathogens.     

Electrical signaling and photosynthesis: Can they co-exist together?

Mechanical irritation of trigger hairs and subsequent generation of action potentials have significant impact on photosynthesis and respiration in carnivorous Venus flytrap (Dionaea muscipula). Action potential-mediated inhibition of photosynthesis and stimulation of respiration is confined only to the trap and was not recorded in adjacent photosynthetic lamina. We showed that the main primary target of electrical signals on assimilation is in the dark enzymatic reaction of photosynthesis. Without doubt, the electrical signaling is costly, and the possible co-existence of such type of signals and photosynthesis in plant cell is discussed.Key words: action potential, carnivorous plant, Dionaea muscipula, electrical signaling, photosynthesis, respiration, Venus flytrapTrap closure of the Venus flytrap (Dionaea muscipula) is one of the fastest movements in plant kingdom. Mechanical irritation of trigger hairs protruding from upper leaf epidermis results in generation of action potential. At room temperature, two touches generate two action potentials and activate the trap snap shut in a fraction of second.¹ After the rapid movement secures the prey, struggling results in generation of further action potentials which cease to occur when the prey stops moving.² We documented that trigger hair irritation and subsequent generation of action potentials have significant effect on photosynthesis and respiration. Action potentials propagate in the trap and were not recorded in adjacent lamina (Fig. 1). This is in accordance with the observation that no changes of photosynthetic and respiration rate as well as effective quantum yield of photosystem II photochemistry were recorded in lamina. Detailed analysis of chlorophyll fluorescence kinetics revealed that the main primary target of action potentials is in the dark enzymatic reaction of photosynthesis and changes in quantum yield of primary photochemistry are just a consequence of decreased CO₂ fixation. However, electrical signals have probably also small effect on excitation energy trapping, charge stabilization and recombination reaction in photosystem II as measurements of fast chlorophyll a fluorescence transient indicates. This effect may be explained by repulsion of charges in reaction center of photosystem II.^3,4 The changes of photosynthesis upon impact of electrical signals probably have no benefit for plant and are only a negative consequences caused by the changes of the ionic environment.Open in a separate windowFigure 1Dionaea muscipula with entrapped wasp of the genus Polistes. Action potentials and rate of net assimilation at irradiance 80 µmol m⁻²s⁻ PAR (A_n) in response to 15 s mechanical trigger hair irritation (between 160–175 s) in trap (upper row) and photosynthetic lamina (lower row).These findings may have more consequences for plants in general. The electrical activity of plant cell was for the first time described by Burdon-Sanderson in 1873.⁵ Hence electrical signals do not belong exclusively to animal kingdom however they never develop the same degree of complexity as in animal nerves. Electrical signals are capable of transmitting signals more quickly over long distances when compared with chemical signals (e.g., hormones).^6,7 They are not confined only to the sensitive plants (e.g., Mimosa, Dionaea), but play also an important role in every non-sensitive plants and in both groups have significant effect on photosynthesis and respiration.^8–14 It is not surprising, that if electrical signals are costly in term of consumption of ATP and increased respiration with concurrent inhibition of photosynthesis, the same degree of complexity as in animals could not be developed. If plant growth depends on photosynthesis, this raises the question whether electrical signals and photosynthesis may co-exist together. The continuous electrical activity would inhibit the main source of energy for plants—photosynthetic assimilation. This may also explain why the plants are sessile organisms. For rapid coordinated movements, electrical activity plays an important role in animals. Unlike animals, plants usually rely on slow movements in which the role of plant hormones is indispensable. In this concept, it is not surprising that the more complex electrical activity was recorded in root transition zone—the heterotrophic part of plant body.^15,16 And this may also explain why the more evident electrical activity in the plant world has evolved in the traps of carnivorous plants like Dionaea, Aldrovanda or Drosera.^17–19 In general the traps of carnivorous plants are considered to be less efficient in photosynthesis.²⁰ Any of the action potentials produced by Drosera tentacles or Dionaea trap do not spread to photosynthetic active lamina, thus the main side of CO₂ fixation is protected.²¹ It is possible that such temporal carbon costs associated with insect trapping and retention may be outweighed by the benefits gained later from the prey—increased nitrogen concentration in the leaves stimulates photosynthetic assimilation.²² The possible ecophysiological impact of electrical signals on daily carbon gain in sensitive plants remains to be elucidated. We still do not completely understand the electrical signals in plants, and further research in this area is necessary to understand the full meaning of electrical activity in plants.     

Sex-biased survival and philopatry in birds: Do they interact?

A review of studies of sex-biased dispersal and philopatry and sex-biased survival in birds is presented. The comparison between sex-related mortality and natal and breeding dispersal at the species-level shows that dispersing birds (mainly females) suffer higher mortality, while philopatric birds (mainly males) have higher survival. The interaction between sex-biased survival and spatial behavior is a crucial component of avian vital strategy, which determine population dynamics and genetic structure.     

Do Alix and ALG‐2 really control endosomes for better or for worse?

Alix/AIP1 (ALG-2-interacting protein X/apoptosis-linked-gene-2-interacting protein 1) is an adaptor protein that was first described for its capacity to bind to the calcium-binding protein ALG-2 (apoptosis-linked gene 2), the expression of which seemed necessary for cell death. Over-expression of truncated forms of Alix blocks caspase-dependent and -independent mechanisms of cell death. Numerous observations in yeast and in mammalian cells suggest that Alix controls the making of and trafficking through endosomes called MVBs (multivesicular bodies), which are crucial intermediates within the endolysosomal system. In particular, deletion of Bro1, one of the yeast homologues of Alix, leads to an impairment in the function of MVBs, leading to mis-sorting of proteins normally destined to the vacuole. Mammalian Alix may have a similar function and has been shown to bind to lyso(bis)phosphatidic acid, ESCRT (endosomal sorting complex required for transport) proteins, endophilins and CIN85 (Cbl-interacting protein of 85 kDa), which are all main regulators of the endosomal system. EIAV (equine infectious anaemia virus) and HIV late domains use Alix to recruit the ESCRT machinery in order to bud from the cell surface, underscoring the crucial role of the protein in orchestrating membrane deformation. In this review I develop the hypothesis that the normal function of Alix in the endolysosomal system may be deviated by ALG-2 towards a destructive role during active cell death.     

Immunometabolism and the modulation of immune responses and host defense: A role for methylglyoxal?

The immune system plays an essential role in protecting the body against pathogens. Immune cells are activated during infections, resulting in a metabolic shift from oxidative phosphorylation to glycolysis. During glycolysis, methylglyoxal (MGO) can be formed as a by-product. As a highly reactive dicarbonyl compound, MGO can rapidly react with proteins to form advanced glycation end products (AGEs). MGO and MGO-derived AGEs have been implicated in the development of insulin resistance, type 2 diabetes and its complications and several other age-related inflammatory diseases. MGO has been found in adipose tissue, atherosclerosis plaques and inflamed livers. Aside from the potential harmful role of MGO, there are studies showing beneficial effects of MGO as a defense mechanism during infections and diseases. In this review, we summarize anti-microbial effects of MGO and the link between MGO and immune cell activation, as potential mediator during host defense.     

Do employers discriminate against obese employees? Evidence from individuals who are simultaneously self-employed and working for an employer

We test whether the lower wages of obese employees result from employer discrimination using a novel empirical strategy. Using data from two nationally representative surveys from the US, we analyze the wages of individuals who are simultaneously self-employed and working for an employer. While lower productivity and customer discrimination against obese individuals may affect wages in both types of jobs, employer discrimination cannot affect the wages of solo entrepreneurs. Our estimates suggest that, even after controlling for productivity (proxied by their concurrent wage in self-employment), white women (men) who are obese earn 11.4% (9.7%) less than their healthy-weight counterparts in their paid employment jobs. We also find that white women (but not men) who are overweight earn 9.1% less than their healthy-weight counterparts. We do not find any evidence of significant bodyweight discrimination among black and Hispanic workers. These results suggest that white workers, especially white women, are likely to face bodyweight discrimination in their workplaces. We report the results for a series of robustness checks to rule out alternative explanations, such as reverse causality, differences in healthcare costs, and occupation-specific customer discrimination.     

Transportsomes and channelsomes: are they functional units for physiological responses?

Channels and transporters play essential biological roles primarily through the transportation of ions and small molecules that are required to maintain cellular activities across the biomembrane. Secondary to transportation, channels and transporters also integrate and coordinate biological functions at different levels, ranging from the subcellular (nm) to multicellular (μm) scales. This is underpinned by efficient functional coupling within molecular assemblies of channels, transporters, proteins, small molecules, and lipids. Molecular interactions create local microenvironments that, in some cases, uniquely modify the functional properties of the channels and transporters. These molecular assemblies built around a transporter or channel (“transportsomes” and “channelsomes”) can be considered as physiological functional units. In this special issue, we provide an overview of recent progress in our understanding of protein-protein and molecular interactions in transportsomes and channelsomes, which occur through both direct molecular contacts and more distal functional coupling, and examine the validity of these “somes”.     

European medicinal mushrooms: Do they have potential for modern medicine? – An update

BackgroundThe application of mushrooms for health purposes has a long tradition and is very common in Asian countries. This trend is also becoming increasingly popular in the western hemisphere. However, mushrooms from European tradition are being treated in a restrained manner despite having significant potential as drugs or as sources of pure bioactive substances.Aim: The present review provides an overview of the most important mushrooms used in European ethnomedical traditions and explores their pharmacological potential and the challenges for the development of new drugs from these sources of natural products.Method: Mushroom species were selected based on information in old herbal books and dispensaries, uninterrupted use and scientific literature in the PubMed database up to June 2019.Results: Traditional experiences and modern studies have demonstrated that medical mushrooms used in European traditions have promising distinct pharmacological potential mediated through defined mechanisms (anti-tumour, anti-inflammatory, anti-oxidative and anti-bacterial). However, the number of modern chemical, biological and pharmacological studies remains relatively small, and some mushroom species have not been studied at all. Unfortunately, no valid clinical studies can be found. Unlike the case with herbal and fungal drugs from traditional Chinese medicine, we are far from comprehensively exploring this potential.Conclusions: Mushrooms from traditional European medicine have the potential to be used in modern medicine. Considerable research, interdisciplinary collaboration, involvement of the pharmaceutical industry, time and money are necessary to explore this potential not only in the form of dietary supplements but also in the form of approved drugs.     

Recombination in HIV and the evolution of drug resistance: for better or for worse?

The rapid evolution of drug resistance remains a major obstacle for HIV therapy. The capacity of the virus for recombination is widely believed to facilitate the evolution of drug resistance. Here, we challenge this intuitive view. We develop a population genetic model of HIV replication that incorporates the processes of mutation, cellular superinfection, and recombination. We show that cellular superinfection increases the abundance of low fitness viruses at the expense of the fittest strains due to the mixing of viral proteins during virion assembly. Moreover, we argue that whether recombination facilitates the evolution of drug resistance depends critically on how resistance mutations interact to determine viral fitness. Contrary to the commonly held belief, we find that, under the most plausible biological assumptions, recombination is expected to slow down the rate of evolution of multi-drug-resistant virus during therapy.     

Growth and guidance cues for regenerating axons: where have they gone?

Both attractive and repellent cues are required to guide developing axons to their targets in the central nervous system. Critical guidance molecules in the developing brain include the semaphorins, netrins, slits, and ephrins. Current research indicates that many of these molecules and their receptors are expressed in the adult central nervous system (CNS), and that injury can alter the levels of these ligands/receptors. Recent studies have begun the process of elucidating the functions of these receptors in adult mammals, and the effects that they have on the regeneration of adult neurons. This review addresses our current knowledge with respect to the response of adult CNS neurons to axonal injury, interventions for enhancing the survival and regeneration of injured neurons, and the expression of developmental axon guidance cues in the injured mature CNS, with specific focus on the retino-tectal projection.     

Chemosensory and thermal cue responses in the sub-Antarctic moth Pringleophaga marioni: Do caterpillars choose Wandering Albatross nest proxies?

On the South Indian Ocean Province Islands of the sub-Antarctic, most nutrients are processed through a detritus-based food web. On Marion Island, larvae of the moth Pringleophaga marioni are one of the key decomposers. Abundance of these caterpillars is higher in newly abandoned Wandering Albatross (Diomedea exulans) nests than other habitats, and this observation has been explained by hypotheses regarding the thermal and nutrient advantages of nests. These hypotheses require a mechanism for increasing the abundance of caterpillars, since nests are an ephemeral resource, and here, we determine whether caterpillars respond to chemosensory and thermal cues using a laboratory choice chamber approach. Caterpillars show no significant preference for newly abandoned nest material over no other choice, old nest material, and the common mire moss Sanionia uncinata. Caterpillars that are acclimated to warm (15 °C) conditions do prefer lower (5 °C) to higher (15 °C) temperatures, perhaps reflecting negative effects of prolonged exposure to warm temperatures on growth. Caterpillars also show significant avoidance of conspecifics, possibly because of incidental cannibalism previously reported in this species. Thus, we find no empirical support for nest-finding ability in caterpillars based on chemosensory or thermal cues. It is possible that adult females or very early instar caterpillars show such ability, or high caterpillar density and biomass in nests are an incidental consequence of better conditions in the nests or deposition by the birds during nest construction.     

Waiting for Trivers and Willard: Do the rich really favor sons?

Parental investment theory has been put forward as a major evolutionary argument explaining male or female biased birth sex ratio, the Trivers-Willard (T-W) hypothesis, predicting that parents living in good circumstances will bias their investment to sons, whereas parents in poor circumstances will bias their investment toward daughters. Tests of the T-W hypothesis on human beings have shown limited evidence for parents appearing to differentiate their investment to sons or daughters according to the reproductive potential of each sex. The present study tests the T-W hypothesis among a large contemporary Polish sample using first birth interval and extent of breastfeeding as measures of parental investment, and economic status and level of parental education as measures of parental condition. The extents to which parental investment and markers of parental condition vary by sex of the child were examined using log-linear analysis. Weak support for the T-W effect is found among families where fathers were best educated, where a greater proportion of first-born boys are breastfed longer than girls, while the opposite trend is observed among families with fathers with lowest levels of education. Although the present study does not fully support the T-W hypothesis, it gives evidence of greater investment in female offspring at the lower extremes of income, and greater investment in males at higher levels of income.     

Mitochondria and endoplasmic reticulum: Targets for a better insulin sensitivity in skeletal muscle?

Obesity and its associated metabolic disorders represent a major health burden, with economic and social consequences. Although adapted lifestyle and bariatric surgery are effective in reducing body weight, obesity prevalence is still rising. Obese individuals often become insulin-resistant. Obesity impacts on insulin responsive organs, such as the liver, adipose tissue and skeletal muscle, and increases the risk of cardiovascular diseases, type 2 diabetes and cancer. In this review, we discuss the effects of obesity and insulin resistance on skeletal muscle, an important organ for the control of postprandial glucose. The roles of mitochondria and the endoplasmic reticulum in insulin signaling are highlighted and potential innovative research and treatment perspectives are proposed.     

Eight human OPA1 isoforms,long and short: What are they for?

OPA1 is a dynamin-related GTPase that controls mitochondrial dynamics, cristae integrity, energetics and mtDNA maintenance. The exceptional complexity of this protein is determined by the presence, in humans, of eight different isoforms that, in turn, are proteolytically cleaved into combinations of membrane-anchored long forms and soluble short forms. Recent advances highlight how each OPA1 isoform is able to fulfill “essential” mitochondrial functions, whereas only some variants carry out “specialized” features. Long forms determine fusion, long or short forms alone build cristae, whereas long and short forms together tune mitochondrial morphology. These findings offer novel challenging therapeutic potential to gene therapy.     

Ecophysiology of photosynthesis in bryophytes: major roles for oxygen photoreduction and non‐photochemical quenching?

CO₂ fixation in mosses saturates at moderate irradiances. Relative electron transport rate (RETR) inferred from chlorophyll fluorescence saturates at similar irradiance in shade species (e.g. Plagiomnium undulatum, Trichocolea tomentella), but many species of unshaded habitats (e.g. Andreaea rothii, Schistidium apocarpum, Sphagnum spp. and Frullania dilatata) show non‐saturating RETR at high irradiance, with high non‐photochemical quenching (NPQ). In P. undulatum and S. apocarpum, experiments in different gas mixtures showed O₂ and CO₂ as interchangeable electron sinks. Nitrogen + saturating CO₂ gave high RETR and depressed NPQ. In S. apocarpum, glycolaldehyde (inhibiting photosynthesis and photorespiration) depressed RETR in air more at low than at high irradiance; in CO₂‐free air RETR was maintained at all irradiances. Non‐saturating electron flow was not suppressed in ambient CO₂ with 1% O₂. The results indicate high capacity for oxygen photoreduction when CO₂ assimilation is limited. Non‐saturating light‐dependent H₂O₂ production, insensitive to glycolaldehyde, suggests that electron transport is supported by oxygen photoreduction, perhaps via the Mehler‐peroxidase reaction. Consistent with this, mosses were highly tolerant to paraquat, which generates superoxide at photosystem I (PSI). Protection against excess excitation energy in mosses involves high capacity for photosynthetic electron transport to oxygen and high NPQ, activated at high irradiance, alongside high reactive oxygen species (ROS) tolerance.     

Do individuals in better condition survive for longer? Field survival estimates according to male alternative reproductive tactics and sex

There is a gap in terms of the supposed survival differences recorded in the field according to individual condition. This is partly due to our inability to assess survival in the wild. Here we applied modern statistical techniques to field‐gathered data in two damselfly species whose males practice alternative reproductive tactics (ARTs) and whose indicators of condition in both sexes are known. In Paraphlebia zoe, there are two ART: a larger black‐winged (BW) male which defends mating territories and a smaller hyaline‐winged (HW) male that usually acts as a satellite. In this species, condition in both morphs is correlated with body size. In Calopteryx haemorrhoidalis, males follow tactics according to their condition with males in better condition practicing a territorial ART. In addition, in this species, condition correlates positively with wing pigmentation in both sexes. Our prediction for both species was that males practicing the territorial tactic will survive less longer than males using a nonterritorial tactic, and larger or more pigmented animals will survive for longer. In P. zoe, BW males survived less than females but did not differ from HW males, and not necessarily larger individuals survived for longer. In fact, size affected survival but only when group identity was analysed, showing a positive relationship in females and a slightly negative relationship in both male morphs. For C. haemorrhoidalis, survival was larger for more pigmented males and females, but size was not a good survival predictor. Our results partially confirm assumptions based on the maintenance of ARTs. Our results also indicate that female pigmentation, correlates with a fitness component – survival – as proposed by recent sexual selection ideas applied to females.