The cornerstone of autotrophy, the CO₂-fixing enzyme, D-ribulose1,5-bisphosphate carboxylase/oxygenase (Rubisco), is hamstrung by slow catalysis and confusion between CO₂ and O₂ as substrates, an ..."abominably perplexing" puzzle, in Darwin's parlance. Here we argue that these characteristics stem from difficulty in binding the featureless CO₂ molecule, which forces specificity for the gaseous substrate to be determined largely or completely in the transition state. We hypothesize that natural selection for greater CO₂/O₂ specificity, in response to reducing atmospheric CO₂:O₂ ratios, has resulted in a transition state for CO₂ addition in which the CO₂ moiety closely resembles a carboxylate group. This maximizes the structural difference between the transition states for carboxylation and the competing oxygenation, allowing better differentiation between them. However, increasing structural similarity between the carboxylation transition state and its carboxyketone product exposes the carboxyketone to the strong binding required to stabilize the transition state and causes the carboxyketone intermediate to bind so tightly that its cleavage to products is slowed. We assert that all Rubiscos may be nearly perfectly adapted to the differing CO₂, O₂, and thermal conditions in their subcellular environments, optimizing this compromise between CO₂/O₂ specificity and the maximum rate of catalytic turnover. Our hypothesis explains the feeble rate enhancement displayed by Rubisco in processing the exogenously supplied carboxyketone intermediate, compared with its nonenzymatic hydrolysis, and the positive correlation between CO₂/O₂ specificity and $^{12}C/^{13}C$ fractionation. It further predicts that, because a more product-like transition state is more ordered (decreased entropy), the effectiveness of this strategy will deteriorate with increasing temperature.
Evolutionary transitions from hermaphroditism to dioecy have been common in flowering plants,1,2 but recent analysis also points to frequent reversions from dioecy to hermaphroditism.2–4 Here, we use ...experimental evolution to expose a mechanism for such reversions, validating an explanation for the scattered phylogenetic distribution of dioecy. We removed males from dioecious populations of the wind-pollinated plant Mercurialis annua and allowed natural selection to act on the remaining females that occasionally produced male flowers; such “leaky” sex expression is common in both males and females of dioecious plants.5 Over the course of four generations, females evolved a 23-fold increase in average male flower production. This phenotypic masculinization of females coincided with the evolution of partial self-fertilization, high average seed set in the continued absence of males, and a capacity to sire progeny when males were re-introduced into their populations. Our study thus validates a mechanism for the rapid dissolution of dioecy and the evolution of functional hermaphroditism under conditions that may frequently occur during periods of low population density, repeated colonization, or range expansion.6,7 Our results illustrate the power of natural selection, acting in replicated experimental populations, to bring about transitions in the mating behavior of plants.
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•Females without male mates evolved to produce increasing numbers of male flowers•Evolved females continued to sire progeny in competition with re-introduced males•Evolved females enjoyed reproductive assurance and an ability to outcross•Observed rates of evolution in the experiment were among the highest yet recorded
Cossard et al. remove males from experimental populations of a dioecious plant and observe a striking increase over several generations in the production of male flowers in females, promoting high siring success. When males are re-introduced into the populations, the evolved hermaphrodites continue to sire seeds, now largely through selfing.
Premise
Plants with separate sexes often show “inconstant” or “leaky” sex expression, with females or males producing a few flowers of the opposite sex. The frequency and degree of such inconstancy ...may reflect residual hermaphroditic sex allocation after an evolutionary transition from combined to separate sexes. Sex inconstancy also represents a possible first step in the breakdown of dioecy back to hermaphroditism. In the Mercurialis annua (Euphorbiaceae) species complex, monoecy and androdioecy have evolved from dioecy in polyploid populations. Here, we characterize patterns of sex inconstancy in dioecious M. annua and discuss how sex inconstancy may have contributed to the breakdown of separate sexes in the genus.
Methods
We measured sex inconstancy in three common gardens of M. annua over 2 years using a modification of Lloyd's phenotypic gender in terms of frequency and degree, with the degree calibrating inconstancy against the sex allocation of constant males and constant females, yielding a measure of gender that does not depend on the distribution of gender in the population.
Results
Unusually for dioecious plants, the frequency of sex inconstancy in M. annua was greater in females, but its degree was greater for males in the 2 years of study. We suggest that this pattern is consistent with the maintenance of inconstancy in dioecious M. annua by selection for reproductive assurance under mate limitation.
Conclusions
Our study illustrates the utility of decomposing measures of sex inconstancy into its frequency and its degree and throws new light on the origin of variation in sexual systems in Mercurialis.
Some microbial eukaryotes, such as the extremophilic red alga Galdieria sulphuraria, live in hot, toxic metal-rich, acidic environments. To elucidate the underlying molecular mechanisms of ...adaptation, we sequenced the 13.7-megabase genome of G. sulphuraria. This alga shows an enormous metabolic flexibility, growing either photoautotrophically or heterotrophically on more than 50 carbon sources. Environmental adaptation seems to have been facilitated by horizontal gene transfer from various bacteria and archaea, often followed by gene family expansion. At least 5% of protein-coding genes of G. sulphuraria were probably acquired horizontally. These proteins are involved in ecologically important processes ranging from heavy-metal detoxification to glycerol uptake and metabolism. Thus, our findings show that a pan-domain gene pool has facilitated environmental adaptation in this unicellular eukaryote.
In dioecious plants, males and females frequently show ‘leaky’ sex expression, with individuals occasionally producing flowers of the opposite sex. This leaky sex expression may have enabled the ...colonization of oceanic islands by dioecious plant species, and it is likely to represent the sort of variation upon which selection acts to bring about evolutionary transitions from dioecy to hermaphroditism. Although leakiness is commonly reported for dioecious species, it is not known whether it has plastic component. The question is interesting because males or females with an ability to enhance their leakiness plastically in the absence of mates would have an advantage of being able to produce progeny by self‐fertilization. Here, we demonstrate that leaky sex expression in the wind‐pollinated dioecious herb Mercurialis annua is plastically responsive to its mating context. We compared experimental populations of females growing either with or without males. Females growing in the absence of males were leakier in their sex expression than controls growing with males, producing more than twice as many male flowers. Our results thus provide a striking instance of plasticity in the reproductive behaviour of plants that is likely adaptive. We consider how females might sense their mating environment as a function of pollen availability, and we discuss possible constraints on the evolution of plasticity in sex expression when the environmental signals that individuals receive are unreliable.
Cossard and Pannell find that females of the dioecious wind‐pollinated colonizing plant Mercurialis annua were substantially more likely to show ‘leaky’ sex expression by the production of male flowers when grown in the absence of males than in their presence. Such plasticity in sex expression would be advantageous during colonization, because M. annua females producing a few male flowers produce seeds by self‐fertilization.
Objective This epidemiological study measured the prevalence of chronic venous disease (CVD) in Belgium and Luxembourg. Possible risk factors and the symptomatology were evaluated. Material and ...methods A survey was carried out in Belgium and Luxembourg between May and September 2013. Patient recruitment was carried out by 406 general practitioners (GPs). Each GP screened 10–20 consecutive patients older than 18 years, and in total 6009 patients were included. Patient characteristics, prevalence of risk factors, symptomatology, and C-classification were noted. The GPs diagnosed CVD and measured the need for treatment. Patients with diagnosed CVD completed a questionnaire about their history of leg problems and a quality of life score (CIVIQ-14). These data were converted into a CIVIQ Global Index Score (GIS). Results The mean age of the patients was 53.4 years, and they were predominantly female (67.5%). Among the 3889 symptomatic patients, heavy legs, pain, and sensation of leg swelling were the most common complaints. Among the included patients, 61.3% of patients were classified within C1-C6; however, only 45.9% of these patients were considered by the GPs to be suffering CVD. Treatment was offered to 49.5% of patients. Age and female gender correlate with a higher C-class ( p < .001). Patients with a higher C-class (C3-C6) have significantly more pain, sensation of swelling and burning, night cramps, itching, and the sensation of “pins and needles” in the legs. Patients taking regular exercise and without a family history had a lower C-class. Higher BMI, age, female gender, family history, history of thrombophlebitis, and a higher C-class correlated with a lower GIS ( p < .001). Of the patients with CVD, 10.4% had lost days of work because of their venous leg problems. Conclusion CVD is a very common disease, which is underestimated. The prevalence increases with age, generates incapacity to work, and worsens the patients' quality of life.
Herein we report the first example of the controlled synthesis of linear and hyperbranched copolymers of 2-methylene-1,3-dioxepane (MDO) with functional vinyl monomers to deliver a range of ...functional, degradable polymers by reversible deactivation radical polymerization. The copolymerization was able to be tuned to vary the incorporation of degradable segments to create degradable materials with predictable molar mass, low dispersity values while also featuring side-chain functionality. The formation of nanoparticles by the addition of divinyladipate to form degradable hyperbranched copolymers was proven by DLS and TEM analyses.
Adipose stem cells (ASCs) have multilineage differentiation capacity and hold great potential for regenerative medicine. Compared to bone marrow-derived mesenchymal stem cells (bmMSCs), ASCs are ...easier to isolate from abundant sources with significantly higher yields. It is generally accepted that bmMSCs show age-related changes in their proliferation and differentiation potentials, whereas this aspect is still controversial in the case of ASCs. In this review, we evaluated the existing data on the effect of donor age on the osteogenic potential of human ASCs. Overall, a poor agreement has been achieved because of inconsistent findings in the previous studies. Finally, we attempted to delineate the possible reasons behind the lack of agreements reported in the literature. ASCs represent a heterogeneous cell population, and the osteogenic potential of ASCs can be influenced by donor-related factors such as age, but also gender, lifestyle, and the underlying health and metabolic state of donors. Furthermore, future studies should consider experimental factors in in vitro conditions, including passaging, cryopreservation, culture conditions, variations in differentiation protocols, and readout methods.
Sexual dimorphism in morphology, physiology or life history traits is common in dioecious plants at reproductive maturity, but it is typically inconspicuous or absent in juveniles. Although plants of ...different sexes probably begin to diverge in gene expression both before their reproduction commences and before dimorphism becomes readily apparent, to our knowledge transcriptome-wide differential gene expression has yet to be demonstrated for any angiosperm species.
The present study documents differences in gene expression in both above- and below-ground tissues of early pre-reproductive individuals of the wind-pollinated dioecious annual herb, Mercurialis annua, which otherwise shows clear sexual dimorphism only at the adult stage.
Whereas males and females differed in their gene expression at the first leaf stage, sex-biased gene expression peaked just prior to, and after, flowering, as might be expected if sexual dimorphism is partly a response to differential costs of reproduction. Sex-biased genes were over-represented among putative sex-linked genes in M. annua but showed no evidence for more rapid evolution than unbiased genes.
Sex-biased gene expression in M. annua occurs as early as the first whorl of leaves is produced, is highly dynamic during plant development and varies substantially between vegetative tissues.
Nitrogen assimilation in leaves requires primary NH₂ acceptors that, in turn, originate from primary carbon metabolism. Respiratory metabolism is believed to provide such acceptors (such as ...2-oxoglutarate), so that day respiration is commonly seen as a cornerstone for nitrogen assimilation into glutamate in illuminated leaves. However, both glycolysis and day respiratory CO₂ evolution are known to be inhibited by light, thereby compromising the input of recent photosynthetic carbon for glutamate production. In this study, we carried out isotopic labelling experiments with ¹³CO₂ and ¹⁵N-ammonium nitrate on detached leaves of rapeseed (Brassica napus), and performed ¹³C- and ¹⁵N-nuclear magnetic resonance analyses. Our results indicated that the production of ¹³C-glutamate and ¹³C-glutamine under a ¹³CO₂ atmosphere was very weak, whereas ¹³C-glutamate and ¹³C-glutamine appeared in both the subsequent dark period and the next light period under a ¹²CO₂ atmosphere. Consistently, the analysis of heteronuclear (¹³C-¹⁵N) interactions within molecules indicated that most ¹⁵N-glutamate and ¹⁵N-glutamine molecules were not ¹³C labelled after ¹³C/¹⁵N double labelling. That is, recent carbon atoms (i.e. ¹³C) were hardly incorporated into glutamate, but new glutamate molecules were synthesized, as evidenced by ¹⁵N incorporation. We conclude that the remobilization of night-stored molecules plays a significant role in providing 2-oxoglutarate for glutamate synthesis in illuminated rapeseed leaves, and therefore the natural day : night cycle seems critical for nitrogen assimilation.
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