Elevated acetyl‐CoA by amino acid recycling fuels microalgal neutral lipid accumulation in exponential growth phase for biofuel production

Microalgal neutral lipids [mainly in the form of triacylglycerols (TAGs)], feasible substrates for biofuel, are typically accumulated during the stationary growth phase. To make microalgal biofuels economically competitive with fossil fuels, generating strains that trigger TAG accumulation from the exponential growth phase is a promising biological approach. The regulatory mechanisms to trigger TAG accumulation from the exponential growth phase (TAEP) are important to be uncovered for advancing economic feasibility. Through the inhibition of pyruvate dehydrogenase kinase by sodium dichloroacetate, acetyl‐CoA level increased, resulting in TAEP in microalga Dunaliella tertiolecta. We further reported refilling of acetyl‐CoA pool through branched‐chain amino acid catabolism contributed to an overall sixfold TAEP with marginal compromise (4%) on growth in a TAG‐rich D. tertiolecta mutant from targeted screening. Herein, a three‐step α loop‐integrated metabolic model is introduced to shed lights on the neutral lipid regulatory mechanism. This article provides novel approaches to compress lipid production phase and heightens lipid productivity and photosynthetic carbon capture via enhancing acetyl‐CoA level, which would optimize renewable microalgal biofuel to fulfil the demanding fuel market.     

Genetic dissection of pre‐anthesis sub‐phase durations during the reproductive spike development of wheat

Flowering time is an important factor affecting grain yield in wheat. In this study, we divided reproductive spike development into eight sub‐phases. These sub‐phases have the potential to be delicately manipulated to increase grain yield. We measured 36 traits with regard to sub‐phase durations, determined three grain yield‐related traits in eight field environments and mapped 15 696 single nucleotide polymorphism (SNP, based on 90k Infinium chip and 35k Affymetrix chip) markers in 210 wheat genotypes. Phenotypic and genetic associations between grain yield traits and sub‐phase durations showed significant consistency (Mantel test; r = 0.5377, P < 0.001). The shared quantitative trait loci (QTLs) revealed by the genome‐wide association study suggested a close association between grain yield and sub‐phase duration, which may be attributed to effects on spikelet initiation/spikelet number (double ridge to terminal spikelet stage, DR‐TS) and assimilate accumulation (green anther to anthesis stage, GA‐AN). Moreover, we observed that the photoperiod‐sensitivity allele at the Ppd‐D1 locus on chromosome 2D markedly extended all sub‐phase durations, which may contribute to its positive effects on grain yield traits. The dwarfing allele at the Rht‐D1 (chromosome 4D) locus altered the sub‐phase duration and displayed positive effects on grain yield traits. Data for 30 selected genotypes (from among the original 210 genotypes) in the field displayed a close association with that from the greenhouse. Most importantly, this study demonstrated specific connections to grain yield in narrower time windows (i.e. the eight sub‐phases), rather than the entire stem elongation phase as a whole.     

Estimation of density threshold of gregarization of desert locust hoppers from field sampling in Mauritania

For desert locusts, Schistocerca gregaria (Forskål) (Orthoptera: Acrididae), the hopper density threshold of gregarization remains poorly documented. Field sampling was carried out in traditional seasonal breeding areas of Mauritania during two successive years without invasion to approximate the gregarization threshold. Hopper densities were assessed at numerous sampling sites. Vegetation was also sampled to characterize the habitats. Hopper behavior was analyzed in situ with the help of a behavioral circular arena to test our assumptions on empirical locust phases determination based on physical appearance (coloration and behavior) following FAO guidelines. The results provided a critical density value around 2.45 hoppers m^?2, above which gregarious hoppers were expected to be seen more frequently in nature. Hopper density was confirmed as the main factor explaining the presence of gregarious individuals. The level of involvement of vegetation parameters such as plant density, basal area, volume, distance between plants, greenness, or combinations of these indicators was low in explaining the observation of gregarious hoppers compared with hopper density. Vegetation cover and height were the only vegetation characteristics that could enhance the prediction of phase status with hopper density. The hoppers' phase determined from their behavior observed in the arena was similar to that characterized through FAO guidelines phase assessment, making consistent the field sampling method. Additionnally, the use of this arena illustrated that the grouping behavior of hoppers is a gradual response to density. This study can be seen as a step forward in the estimation of hopper density thresholds of gregarization in the field. This should improve the decision making for intervention during preventive control operations.     

Importance of solitarious desert locust population dynamics: lessons from historical survey data in Algeria

The desert locust, Schistocerca gregaria (Forskål) (Orthoptera: Acrididae), is a major pest and well known in its gregarious phase. However, it is not well understood during recession periods, when the solitarious phase populations are discrete. Nonetheless, these populations are at the origin of the invasions when ecological conditions become favourable. This lack of knowledge of the solitarious phase individuals impedes effective preventive management of this pest. Archive data collected in Algeria from 1980 to 2011 were used to analyse solitarious population dynamics across the Algerian Sahara where some outbreak areas are located that play a major role in the invasion process. The results confirm previous empirical observations on solitarious population dynamics. First, a clear difference could be documented between the northern and southern Saharan regions of Algeria concerning the locust dynamics and the impact of environmental conditions. The importance of runoff was clear to create suitable habitats over a long period and to very distant places from rainy areas. Second, a link, on an annual basis, between green vegetation and presence of solitarious locusts was found. Third, statistical relationships between various locations demonstrated a clear regional dynamics. Our study confirmed the importance of migrations of solitarious populations among Algerian regions and more generally within the recession area of this species. The operational implications of these findings are multiple. First, they confirm the need of a flexible and scalable preventive system during the year, from 1 year to another and with a clear distinction between the northern and southern Saharan areas of Algeria. Second, they also confirm the necessity for the inclusion of wadis and soil moisture estimations from remote sensing in geographic information systems for preventive management. And third, they clearly illustrate the importance to target solitarious locusts for more efficient preventive survey operations.     

A quantitative real‐time PCR assay for identification and enumeration of the occasionally co‐occurring ichthyotoxic Pseudochattonella farcimen and P. verruculosa (Dictyochophyceae) and analysis of variation in gene copy numbers during the growth phase of single and mixed cultures

The ichthyotoxic genus Pseudochattonella forms recurrent extensive blooms in coastal waters in Japan, New Zealand and Northern Europe. It comprises of two morphologically similar species, P. verruculosa and P. farcimen, which complicates visual species identification and enumeration of live and fixed material. Primers designed previously could not quantitatively distinguish species in mixed assemblages. To address this issue we developed two primer sets: one revealed itself to be genus specific for Pseudochattonella and the other species‐specific for P. verruculosa. By subtracting cell estimates for P. verruculosa from combined results we could calculate cell numbers for P. farcimen. This approach has overcome the challenges posed by the very limited sequence availability and low gene variability between the two species. The qPCR assay was extensively tested for specificity, efficiency and sensitivity over an entire growth cycle in both single and mixed assemblages. Comparison of cell abundance estimates obtained by qPCR assay and microscopy showed no statistically significant difference until stationary and death phases. The assay was also tested on environmental samples collected during a small Pseudochattonella bloom in Denmark in March–April 2015. It was impossible to distinguish P. farcimen and P. verruculosa by light microscopy but qPCR showed both species were present. The two methods provided nearly identical cell numbers but the assay provided discrimination and enumeration of both species.     

Effect of vegetation on density thresholds of adult desert locust gregarization from survey data in Mauritania

In the desert locust, Schistocerca gregaria (Forskål) (Orthoptera: Acrididae), the threshold density inducing the gregarization phenomenon has never been determined under natural conditions. The influence of environmental factors on this phenomenon has been studied mostly in controlled environments. Based on data collected during several years by the survey teams of the National Center for Locust Control in Mauritania, we analyzed the influence of locust density, vegetation cover, and vegetation status on the probability of observing gregarious locusts. We assumed that a probability to observe gregarious locusts of 0.5 corresponded to the density threshold of gregarization. The results showed in detail the change in the threshold of gregarization according to the cover and status of the vegetation. Low cover and dry vegetation led to a low density threshold of gregarization probably due to high probability of individuals to touch each other. Dense and green vegetation favored a high threshold of gregarization probably due to a dispersion of the individuals and a low probability of individual encounters. These findings should help the management of locusts and decision making during control operations.     

Aroma Profile of Rubus ulmifolius Flowers and Fruits During Different Ontogenetic Phases

The chemical composition of spontaneous volatile emission from Rubus ulmifolius flowers and fruits during different stages of development was evaluated by HS‐SPME‐GC/MS. In total, 155 chemical compounds were identified accounting 84.6 – 99.4% of whole aroma profile of flowers samples and 92.4 – 96.6% for fruit samples. The main constituents were α‐copaene, β‐caryophyllene, germacrene D, (E,E)‐α‐farnesene, 1,7‐octadien‐3‐one,2‐methyl‐6‐methylene, tridecane, (E)‐2‐hexenol acetate, (E)‐3‐hexenol acetate and cyperene. The results give a chemotaxonomic contribution to the characterization of the VOCs emitted from flowers and fruits during their ontogenic development.     

A Dual Role by Incorporation of Magnesium in YbZn2Sb2 Zintl Phase for Enhanced Thermoelectric Performance

1‐2‐2‐type Zintl phase compounds have promising thermoelectric properties because of their complex crystal structures and multiple valence‐band structures. In this work, a series of single phase (Yb_0.9Mg_0.1)Mg_xZn_2?xSb₂ (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) compounds are prepared by alloying YbZn₂Sb₂ with 10 at% MgZn₂Sb₂ and different amounts of YbMg₂Sb₂. The incorporation of Mg at the Yb site, as well as at the Zn site, not only leads to an effective orbital alignment confirmed by the dramatically enhanced density of states effective mass and Seebeck coefficients, but also increases the point defect scattering, contributing to a low lattice thermal conductivity ≈0.54 W m^?1 K^?1 at 773 K. Combined with the optimization of the carrier concentration by Ag doping at the Zn site, a highest ZT value ≈1.5 at 773 K is achieved in (Yb_0.9Mg_0.1)Mg_0.8Zn_1.2Ag_0.002Sb₂, which is higher than that of all the previously reported 1‐2‐2‐type Zintl phase compounds.     

Leaf stable carbon isotope composition reflects transpiration efficiency in Zea mays

The increasing demand for food production and predicted climate change scenarios highlight the need for improvements in crop sustainability. The efficient use of water will become increasingly important for rain‐fed agricultural crops even in fertile regions that have historically received ample precipitation. Improvements in water‐use efficiency in Zea mays have been limited, and warrant a renewed effort aided by molecular breeding approaches. Progress has been constrained by the difficulty of measuring water‐use in a field environment. The stable carbon isotope composition (δ¹³C) of the leaf has been proposed as an integrated signature of carbon fixation with a link to stomatal conductance. However, additional factors affecting leaf δ¹³C exist, and a limited number of studies have explored this trait in Z. mays. Here we present an extensive characterization of leaf δ¹³C in Z. mays. Significant variation in leaf δ¹³C exists across diverse lines of Z. mays, which we show to be heritable across several environments. Furthermore, we examine temporal and spatial variation in leaf δ¹³C to determine the optimum sampling time to maximize the use of leaf δ¹³C as a trait. Finally, our results demonstrate the relationship between transpiration and leaf δ¹³C in the field and the greenhouse. Decreasing transpiration and soil moisture are associated with decreasing leaf δ¹³C. Taken together these results outline a strategy for using leaf δ¹³C and reveal its usefulness as a measure of transpiration efficiency under well‐watered conditions rather than a predictor of performance under drought.     

BrpSPL9 (Brassica rapa ssp. pekinensis SPL9) controls the earliness of heading time in Chinese cabbage

The leafy heads of cabbage (Brassica oleracea), Chinese cabbage (Brassica rapa ssp. pekinensis), Brussels sprouts (B. oleracea ssp. gemmifera) and lettuce (Lactuca sativa) comprise extremely incurved leaves that are edible vegetable products. The heading time is important for high quality and yield of these crops. Here, we report that BrpSPL9‐2 (B. rapa ssp. pekinensis SQUAMOSA PROMOTER BINDING‐LIKE 9‐2), a target gene of microRNA brp‐miR156, controls the heading time of Chinese cabbage. Quantitative measurements of leaf shapes, sizes, colour and curvature indicated that heading is a late adult phase of vegetative growth. During the vegetative period, miR156 levels gradually decreased from the seedling stage to the heading one, whereas BrpSPL9‐2 and BrpSPL15‐1 mRNAs increased progressively and reached the highest levels at the heading stage. Overexpression of a mutated miR156‐resistant form of BrpSPL9‐2 caused the significant earliness of heading, concurrent with shortening of the seedling and rosette stages. By contrast, overexpression of miR156 delayed the folding time, concomitant with prolongation of the seedling and rosette stages. Morphological analysis reveals that the significant earliness of heading in the transgenic plants overexpressing BrpSPL9‐2 gene was produced because the juvenile phase was absent and the early adult phase shortened, whereas the significant delay of folding in the transgenic plants overexpressing Brp‐MIR156a was due to prolongation of the juvenile and early adult phases. Thus, miR156 and BrpSPL9 genes are potentially important for genetic improvement of earliness of Chinese cabbage and other crops.     

Lipid compositions in diatom Conticribra weissflogii under static and aerated culture conditions

The diatom Conticribra weissflogii is a microalga with high nutrition value, rich in docosahexaenoic acids (DHA) and eicosapentaenoic acids (EPA). In order to study the effect of culture conditions on the changes of lipid compositions, the intact lipid structural profiles and fatty acids in C. weissflogii were monitored under static and aerated culture conditions. The results showed that, lipids identified in C. weissflogii were neutral lipid triacylglycerols (TAG), betaine lipid diacylglycerylcarboxy‐N‐hydroxymethyl‐choline (DGCC), phosphatidylcholine (PC) and four classes of photosynthetic glycerolipids. The profiles of lipid metabolites of C. weissflogii were different between two culture modes, with the following characteristics under aerated conditions: TAGs increased significantly, whereas the levels of sulfoquinovosyl diacylglycerol (SQDG), monogalactosyldiacylglycerol (MGDG), and DGCC decreased. Furthermore, higher contents of EPA‐rich TAG and EPA/DHA‐rich DGCC were detected at the end of stationary phase, while EPA/DHA‐rich PC, EPA‐rich MGDG and EPA‐rich digalactosyldiacylglycerol (DGDG) were obtained in the exponential phase under static conditions. Meanwhile, the contents of almost all classes of the essential fatty acids (EFAs)‐enriched lipids increased at onset of stationary phase under aerated conditions. Taken together, given that the high levels of EFAs are required for artificial rearing of marine organisms, aeration is critically important for increasing the production rate and the contents of EFA molecules and therefore increasing the nutritional value of the microalgae.     

Chronological transition of mitochondrial morphology in Chlamydomonas reinhardtii (Chlorophyceae) poststationary phase growth1

In Chlamydomonas reinhardtii P. A. Dangeard, mitochondrial morphology has been observed during asexual cell division cycle, gamete and zygote formation, zygote maturation, and meiotic stages. However, the chronological transition of mitochondrial morphology after the stationary phase of vegetative growth, defined as the poststationary phase, remains unknown. Here, we examined the mitochondrial morphology in cells cultured for 4 months on agar plates to study mitochondrial dynamics in the poststationary phase. Fluorescence microscopy showed that the intricate thread‐like structure of mitochondria gradually changed into a granular structure via fragmentation after the stationary phase in cultures of about 1 week of age. The number of mitochondrial nucleoids decreased from about 30 per cell at 1 week to about five per cell after 4 months of culture. The mitochondrial oxygen consumption decreased exponentially, but the mitochondria retained their membrane potential. The total quantity of mitochondrial DNA (mtDNA) of cells at 4 months decreased to 20% of that at 1 week. However, the mitochondrial genomic DNA length was unchanged, as intermediate lengths were not detected. In cells in which the total mtDNA amount was reduced artificially to 16% after treatment with 5‐fluoro‐2‐deoxyuridine (FdUrd) for 1 week, the mitochondria remained as thread‐like structures. The oxygen consumption rate of these cells corresponded to that of untreated cells at 1 week of culture. This suggests that a decrease in mtDNA does not directly induce the fragmentation of mitochondria. The results suggest that during the late poststationary phase, mitochondria converge to a minimum unit of a granular structure with a mitochondrial nucleoid.     

How to deal with neglected tropical diseases in the light of an African ethic

Many countries in Africa, and more generally those in the Global South with tropical areas, are plagued by illnesses that the wealthier parts of the world (mainly ‘the West’) neither suffer from nor put systematic effort into preventing, treating or curing. What does an ethic with a recognizably African pedigree entail for the ways various agents ought to respond to such neglected diseases? As many readers will know, a characteristically African ethic prescribes weighty duties to aid on the part of those in a position to do so, and it therefore entails that there should have been much more contribution from the Western, ‘developed’ world. However, what else does it prescribe, say, on the part of sub‐Saharan governments and the African Union, and are they in fact doing it? I particularly seek to answer these questions here, by using the 2013‐16 Ebola crisis in West Africa to illustrate what should have happened but what by and large did not.