Physiological stage drives fungal community dynamics and diversity in Leptospermum scoparium (mānuka) flowers

Flowers are an important niche for microbes, and microbes in turn influence plant fitness. As flower morphology and biology change rapidly over time, dynamic niches for microbes are formed and lost. Floral physiology at each life stage can therefore influence arrival, persistence and loss of microbial species; however, this remains little understood despite its potential consequences for host reproductive success. Through internal transcribed spacer 1 (ITS1) community profiling, we characterized the effect of transitioning through five floral stages of mānuka (Leptospermum scoparium), from immature bud to spent flower, and subsequent allocation to seed, on the flower-inhabiting fungal community. We found nectar-consuming yeasts from Aureobasidium and Vishniacozyma genera and functionally diverse filamentous fungi from the Cladosporium genus dominated the anthosphere. The candidate core microbiota persisted across this dynamic niche despite high microbial turnover, as observed in shifts in community composition and diversity as flowers matured and senesced. The results demonstrated that floral stages are strong drivers of anthosphere fungal community assembly and dynamics. This study represents the first detailed exploration of fungi through floral development, building on fundamental knowledge in microbial ecology of healthy flowers.     

The austral biflagellate Chloromonas rubroleosa (Chlorophyceae) is the closest relative of the unusual quadriflagellate genus Chlainomonas,both found in snow

The quadriflagellate genus Chlainomonas frequently dominates red snow globally. It is unusual in several respects, with two separated pairs of flagella, apparent cell division via extrusion of cytoplasmic threads, and being nested phylogenetically within the biflagellate genus Chloromonas. Here, we showed that the austral species Chloromonas (Cr.) rubroleosa, originally described from Antarctic red snow, is a close biflagellate relative of Chlainomonas, challenging the monophyly of Chlainomonas as currently conceived. Sequences of the 18S rRNA gene robustly linked Cr. rubroleosa with near-identical environmental sequences from Antarctic red snow and Chlainomonas from North America, Japan, and Europe. Furthermore, the 18S rRNA and rbcL gene sequences of Cr. rubroleosa were almost identical to New Zealand and North American collections of Chlainomonas. Cr. rubroleosa and New Zealand Chlainomonas are separated by only a single-base substitution across the ITS1-5.8S-ITS2 rRNA loci (and according to ITS2, the North American collection is the next closest relative). This again raises the possibility that Chlainomonas is a life-cycle stage of vegetatively biflagellate organisms, although this remains confounded by the scarcity of biflagellates in field populations, the apparent cell division by quadriflagellates, and the absence of Chlainomonas-type cells in cultures of Cr. rubroleosa. The latter species is broadly similar to Chlainomonas, being poor at swimming, with similar pigment, chloroplast arrangement and ultrastructure, and is relatively large. Increased size is a feature of the wider clade of “Group D” snow algae. A synthesis of field and laboratory investigations may be needed to unravel the life cycle and correct the systematics of this group.     

Cloning and expression of an anti-LDL(-) single-chain variable fragment,and its inhibitory effect on experimental atherosclerosis

The in vivo modified forms of low-density lipoprotein (LDL) are important for the formation of foam cells and as mediators of the immuno-inflammatory process involved in the progression of atherosclerosis. Electronegative LDL, LDL(-), is a LDL subfraction with pro-inflammatory properties that is present in human blood. To investigate possible atheroprotective effects, an anti-LDL(-) single-chain variable fragment (scFv) was expressed in the methylotrophic yeast Pichia pastoris and its activity was evaluated in vitro against macrophages and in experimental atherosclerosis in Ldlr^-/- mice. The recombinant 2C7 scFv was produced in a yield of 9.5 mg of protein/L. The specificity and affinity of purified 2C7 scFv against LDL(-) was confirmed by ELISA. To assess the activity of 2C7 scFv on foam cell formation, RAW 264.7 macrophages were exposed to LDL(-) in the presence or absence of 2C7 scFv. The 2C7 scFv inhibited the uptake of LDL(-) by macrophages in a dose-dependent manner, and internalization of LDL(-) by these cells was found to be mediated by the CD36 and CD14 receptor. In addition, compared with untreated cells, lipid accumulation in macrophages was decreased, and the expression of Cd36, Tlr-4 and Cox-2 was downregulated in macrophages treated with 2C7 scFv. Importantly, compared with untreated mice, the treatment of Ldlr^-/- mice with 2C7 scFv decreased the atherosclerotic lesion area at the aortic sinus. In conclusion, our data show that 2C7 scFv inhibits foam cell formation and atherosclerotic plaque development by modulating the expression of genes relevant to atherogenesis. These results encourage further use of this antibody fragment in the development of new therapeutic strategies that neutralize the pro-atherogenic effects of LDL(-).     

Short photoperiod attenuates CO2 fertilization effect on shoot biomass in Arabidopsis thaliana

The level of carbon dioxide (CO₂) in the air can affect several traits in plants. Elevated atmospheric CO₂ (eCO₂) can enhance photosynthesis and increase plant productivity, including biomass, although there are inconsistencies regarding the effects of eCO₂ on the plant growth response. The compounding effects of ambient environmental conditions such as light intensity, photoperiod, water availability, and soil nutrient composition can affect the extent to which eCO₂ enhances plant productivity. This study aimed to investigate the growth response of Arabidopsis thaliana to eCO₂ (800 ppm) under short photoperiod (8/16 h, light/dark cycle). Here, we report an attenuated fertilization effect of eCO₂ on the shoot biomass of Arabidopsis plants grown under short photoperiod. The biomass of two-, three-, and four-week-old Arabidopsis plants was increased by 10%, 15%, and 28%, respectively, under eCO₂ compared to the ambient CO₂ (aCO₂, 400 ppm) i.e. control. However, the number of rosette leaves, rosette area, and shoot biomass were similar in mature plants under both CO₂ conditions, despite 40% higher photosynthesis in eCO₂ exposed plants. The levels of chlorophylls and carotenoids were similar in the fully expanded rosette leaves regardless of the level of CO₂. In conclusion, CO₂ enrichment moderately increased Arabidopsis shoot biomass at the juvenile stage, whereas the eCO₂-induced increment in shoot biomass was not apparent in mature plants. A shorter day-length can limit the source-to-sink resource allocation in a plant in age-dependent manner, hence diminishing the eCO₂ fertilization effect on the shoot biomass in Arabidopsis plants grown under short photoperiod.     

Pattern of the evolution of HIV-1 enν gene in C?te d?Ivoire

Cête d׳Ivoire continues to have the highest HIV-1 prevalence rate in West Africa, although the infection number is in constant decline. The external envelope protein of the viruses is a likely site of selection, and responsible for receptor binding and entry into host cells, and therefore constitutes an ideal region with which to investigate the evolutionary processes acting on HIV-1. In this study, we analyse 189 envelope glycoprotein V3 loop region sequences of viruse isolates from 1995 to 2009, from HIV-1 untreated patients living in Cête d׳Ivoire, to decipher the temporal relationship between disease diversity, divergence and selection. Our analyses show that the nonsynonymous and synonymous ratio (dN/dS) was lower than 1 for viral populations analysed within 15 years, which showed the sequences did not undergo adequate immune pressure. The phylogenetic tree of the sequences analysed demonstrated distinctly long internal branches and short external branches, suggesting that only a small number of viruses infected the new host cell at each transmission. In addition to identifying sites under purifying selection, we also identified neutral sites that can cause false positive inference of selection. These sites presented form a resource for future studies of selection pressures acting on HIV-1 enν gene in Cête d׳Ivoire and other West African countries.