Physiologic and Transcriptomic Insights into the High Alkali Response of Dunaliella salina

The halophilic unicellular green alga Dunaliella salina is characterized as the distinct tolerance to high salt in the field.Normally the organism is concurrently subjected with salt and alkali stress,but the feature of D.salina in response to high alkali stress was not investigated before.In this study,we used high pH stress to simulate high alkali stress and found D.salina also showed tolerance to high alkali stress,even grown under pH at 11.0,with high cell density and chlorophyll biosynthesis.High-throughput transcriptome analysis revealed the dramatically different expression of genes associated with nitrogen metabolism,lipid andβ-carotene biosynthesis after high alkali treatment.Furthermore,physiologic analysis showed that high alkali treatment induced the expression and activity of nitrate reductase(NR),which generated nitric oxide(NO)as the messenger,and ultimately induced the accumulation of lipid andβ-carotene biosynthesis.Suppressing NR activity or NO generation also reduced high-alkali-induced lipid andβ-carotene biosynthesis,as well as attenuated the tolerance of D.salina to high alkali stress.Thus,our physiologic and transcriptomic data reveal the novel function of NR-dependent NO signal during the adaptation of D.salina to high alkali stress,through inducing the biosynthesis of lipid andβ-carotene biosynthesis.

RNA interference of a trehalose-6-phosphate synthase gene reveals its roles in the biosynthesis of chitin and lipids in Heortia vitessoides(Lepidoptera:Crambidae)

Trehalose 6-phosphate synthase(TPS),an enzyme that hydrolyzes two glucose molecules to yield trchalose,plays a pivotal role in various physiological processes.In this study,we cloned the trehalose-6-phosphate synthase gene(HvTPS)and investigated its expression patterns in various tssues and d:velopmental stages in Heortia vitessoides Moore(Lepidoptera:Crambidac).HvTPS was highly expressed in the fat body and after pupation or before molting.We knocked down TPS in H.vitessoides by RNA interference and found that 3.0μg of dsHvTPS resulted in optimal interference at 24 h and 36 h post-injection and caused a sharp decline in the survival rate during the 5th instar larval-pupal stage and obviously abnormal or lethal phenotypes.Additionally.compared to the controls,TPS activity and trehalose contents were significantly lower and the glucose content was significantly higher 24 h or 36 h after injection with 3.0μg of dsHIvTPS.Furthermore,the silencing of HvTPS suppressed the cxpression of six key genecs in the chitin biosynthesis pathway and one key gene related to lipid catabolism.The expression levels of two genes associated with lipid biosynthesis were upregulated.These results strongly suggest that HvTPS is essential for the normal growth and development of H.vitessoides and provide a reference for further studies of the utility of key genes involved in chitin and lipid biosynthesis for controlling insect development.

Acetyl coenzyme A carboxylase modulates lipogenesis and sugar homeostasis in Blattella germanica

Lipid and sugar homeostasis is critical for insect development and survival.In this study,we characterized an acetyl coenzyme A carboxylase gene in Blattella germanica(BgACC)that is involved in both lipogenesis and sugar homeostasis.We found that BgACC was dominantly expressed in the fat body and integument,and was significantly upregulated after molting.Knockdown of BgACC in 5th-instar nymphs did not affect their normal molting to the next nymphal stage,but it caused a lethal phenotype during adult emergence.BgACC-RNA interference(RNAi)significantly downregulated total free fatty acid(FFA)and triacylglycerol(TAG)levels,and also caused a significant decrease of cuticular hydrocarbons(CHCs).Repression of BgACC in adult females affected the development of oocytes and resulted in sterile females,but BgACC-RNAi did not affect the reproductive ability of males.Interestingly,knockdown of BgACC also changed the expression of insulin-like peptide genes(BglLPs),which mimicked a physiological state of high sugar uptake.In addition,BgACC was upregulated when B.germanica were fed on a high sucrose diet,and repression of BgACC upregulated the expression of the glycogen synthase gene(BgGlyS).Moreover,BgACC-RNAi increased the circulating sugar levels and glycogen storage,and a longevity assay suggested that BgACC was important for the survival of B.germanica under conditions of high sucrose uptake.Our results confirm that BgACC is involved in multiple lipid biogenesis and sugar homeostasis processes,which further modulates insect reproduction and sugar tolerance.This study benefits our understanding of the crosstalk between lipid and sugar metabolism.

The Chloroplast Outer Envelope Membrane:The Edge of Light and Excitement

The chloroplast is surrounded by a double-membrane envelope at which proteins, ions, and numerous metabolites including nucleotides, amino acids, fatty acids, and carbohydrates are exchanged between the two aqueous phases, the cytoplasm and the chloroplast stroma. The chloroplast envelope is also the location where the biosynthesis and accumulation of various lipids take place. By contrast to the inner membrane, which contains a number of specific transporters and acts as the permeability barrier, the chloroplast outer membrane has often been considered a passive compartment derived from the phagosomal membrane. However, the presence of galactoglycerolipids and β-barrel membrane proteins support the common origin of the outer membranes of the chloroplast envelope and extant cyanobacteria. Furthermore, recent progress in the field underlines that the chloroplast outer envelope plays important roles not only for translocation of various molecules, but also for regulation of metabolic activities and signaling processes. The chloroplast outer envelope membrane offers various interesting and challenging questions that are relevant to the understanding of organelle biogenesis, plant growth and development, and also membrane biology in general.

Membrane-bound O-acyltransferases(MBOATs)

The MBOATenzyme family,identified in 2000,comprises 11 genes in the human genome that participate in a variety of biological processes.MBOAT enzymes contain multiple transmembrane domains and share two active site residues,histidine and asparagine.Several MBOAT members are drug targets for major human diseases,including atherosclerosis,obesity,Alzheimer disease,and viral infections.Here we review the historical aspects of MBOAT enzymes,classify them biochemically into 3 subgroups,and describe the essential features of each member.