Characterisation of Shigella Spa33 and Thermotoga FliM/N reveals a new model for C‐ring assembly in T3SS

Flagellar type III secretion systems (T3SS) contain an essential cytoplasmic‐ring (C‐ring) largely composed of two proteins FliM and FliN, whereas an analogous substructure for the closely related non‐flagellar (NF) T3SS has not been observed in situ. We show that the spa33 gene encoding the putative NF‐T3SS C‐ring component in Shigella flexneri is alternatively translated to produce both full‐length (Spa33‐FL) and a short variant (Spa33‐C), with both required for secretion. They associate in a 1:2 complex (Spa33‐FL/C₂) that further oligomerises into elongated arrays in vitro. The structure of Spa33‐C₂ and identification of an unexpected intramolecular pseudodimer in Spa33‐FL reveal a molecular model for their higher order assembly within NF‐T3SS. Spa33‐FL and Spa33‐C are identified as functional counterparts of a FliM–FliN fusion and free FliN respectively. Furthermore, we show that Thermotoga maritima FliM and FliN form a 1:3 complex structurally equivalent to Spa33‐FL/C₂, allowing us to propose a unified model for C‐ring assembly by NF‐T3SS and flagellar‐T3SS.     

Enantiomeric Neolignans and a Sesquiterpene from Solanum erianthum and Their Absolute Configuration Assignment

One pair of new C‐8–C‐3′/C‐7–O–C‐4′ linked neolignan enantiomers ( 1a / 1b ) and one new guaiane sesquiterpene ( 2 ) first featuring the 1(2),9(10)‐conjugated double bond were isolated from the stems of Solanum erianthum (Solanceae). Their structures were characterized on the basis of extensive spectroscopic analyses, especially from their 2D nuclear magnetic resonance (NMR) spectra. The absolute configurations of 1a / 1b were rigorously elucidated by electronic circular dichroism (ECD) experiments combined with the reversed helicity rule for the 2,3‐dihydrobenzo[b]furan chromophore, and compound 2 is the first report on the sterochemical assignment of a guaiane sesquiterpene by using the allylic axial chirality rule for the conjugated diene chromophore in combination with the calculated ECD spectrum. Chirality 28:259–263, 2016. © 2016 Wiley Periodicals, Inc.     

Differential miRNA expression in maize ear subjected to shading tolerance

Maize is an important crop worldwide. Its grain yield is susceptible to decrease under conditions of abiotic stress, such as shade in subtropical and temperate zones. The genetic basis of shade tolerance has not been determined in maize. MicroRNAs (miRNAs) are known to play critical roles in plant stress responses, including responses to environmental stress; but shade-associated miRNAs have not previously been identified in maize. In this study, the shade-sensitive inbred line 502 was used to examine miRNA expression differences in maize ear, after a 10-day treatment of either shade or exposure to natural light. A total of 130 known miRNAs belonging to 21 families were identified, of which 45 miRNAs were differentially expressed between shaded and natural light treatments. Twelve novel miRNAs were also predicted. In total, 94 miRNAs were upregulated and 48 downregulated in plants exposed to shaded conditions, compared with those exposed to natural light. These differentially expressed miRNAs may participate in regulating hormone homeostasis, metabolism, development and flower timing. These results suggest that the decrease of maize yield under shaded conditions may partly be determined by the differential expression of shade-induced miRNAs.     

Effects of a Standardized Phenolic-Enriched Maple Syrup Extract on β-Amyloid Aggregation,Neuroinflammation in Microglial and Neuronal Cells,and β-Amyloid Induced Neurotoxicity in <Emphasis Type="Italic">Caenorhabditis elegans</Emphasis>

Published data supports the neuroprotective effects of several phenolic-containing natural products, including certain fruit, berries, spices, nuts, green tea, and olive oil. However, limited data are available for phenolic-containing plant-derived natural sweeteners including maple syrup. Herein, we investigated the neuroprotective effects of a chemically standardized phenolic-enriched maple syrup extract (MSX) using a combination of biophysical, in vitro, and in vivo studies. Based on biophysical data (Thioflavin T assay, transmission electron microscopy, circular dichroism, dynamic light scattering, and zeta potential), MSX reduced amyloid β_1?42 peptide (Aβ_1?42) fibrillation in a concentration-dependent manner (50–500 μg/mL) with similar effects as the neuroprotective polyphenol, resveratrol, at its highest test concentration (63.5?% at 500 μg/mL vs. 77.3?% at 50 μg/mL, respectively). MSX (100 μg/mL) decreased H₂O₂-induced oxidative stress (16.1?% decrease in ROS levels compared to control), and down-regulated the production of lipopolysaccharide (LPS)-stimulated inflammatory markers (22.1, 19.9, 74.8, and 87.6?% decrease in NOS, IL-6, PGE₂, and TNFα levels, respectively, compared to control) in murine BV-2 microglial cells. Moreover, in a non-contact co-culture cell model, differentiated human SH-SY5Y neuronal cells were exposed to conditioned media from BV-2 cells treated with MSX (100 μg/mL) and LPS or LPS alone. MSX-BV-2 media increased SH-SY5Y cell viability by 13.8?% compared to media collected from LPS-BV-2 treated cells. Also, MSX (10 μg/mL) showed protective effects against Aβ_1?42 induced neurotoxicity and paralysis in Caenorhabditis elegans in vivo. These data support the potential neuroprotective effects of MSX warranting further studies on this natural product.     

蝇蛆肠道微生物菌群对猪粪残留抗生素的降解及抗性基因的影响

【目的】过度使用抗生素作为动物饲料添加剂,导致畜禽粪便已成为抗生素抗性基因的主要蓄积库,为了研究蝇蛆(Musca domestica)对猪粪中残留抗生素及抗性基因的影响,本文动态采集了实际农场条件下蝇蛆转化过程中猪粪堆体及虫体样本。【方法】利用q PCR、液相色谱-电喷雾质谱、同位素内标法、Illumina高通量测序以及局部相似性研究蝇蛆生物转化过程中残留抗生素降解效能及相关抗性基因组变化的微生物生态机制。【结果】6 d周期内,猪粪中四环素、土霉素、金霉素、强力霉素、磺胺嘧啶、诺氟沙星、氧氟沙星、环丙沙星以及恩诺沙星等9种残留抗生素含量显著下降,累积减量为34.3%–58.1%,每日减量百分比介于7.8%–57.4%之间。猪粪中共检测到的158种抗性基因,其中有118种大幅衰减,衰减量平均达79.3%;23种抗性基因存在富集现象,富集倍数平均为3.48。在蝇蛆肠道的作用下,粪源微生物群落中Bacteroidetes相对丰度下降,Proteobacteria相对丰度增加,尤其是Ignatzschineria增幅最大。网络分析发现,抗性基因的增减与微生物群落的变化显著相关,与抗性基因衰减相关的微生物主要属于Clostridiales和Bacteroidales,而与抗性基因富集相关的微生物主要为Alcaligenaceae、[Weeksellaceae]及Bacillales。【结论】蝇蛆可有效削减猪粪中的残留抗生素及防控抗性基因向环境扩散。     

植物质量、模拟增温及生境对凋落物分解的相对贡献

采用凋落物袋法对比研究了茭草和杉叶藻两种初始质量差异显著的湿地植物凋落物,在模拟增温(1.5～2.0 ℃)及不同生境(大气、大气-水界面与水-土界面)下的质量残留率和不同化学组分的含量变化.结果表明: 在一年的分解周期内,凋落物残留率表现出季节性变化特征,并与环境因子之间存在显著的交互作用.各因子对凋落物分解的贡献大小不同,植物质量解释了28.8%的变异,模拟增温解释了6.3%的变异,而生境解释了34.9%的变异.随着分解时间的延长,凋落物中不同组分(难、易分解)的含量发生明显变化.杉叶藻中氮含量在分解后期显著降低了53.1%,而木质素含量显著增加了45.4%.生境是影响凋落物分解最重要的环境因子,其次是植物质量,而模拟增温对凋落物分解的影响程度较小.     

Phylogeography of rare fern <Emphasis Type="Italic">Polystichum glaciale</Emphasis> endemic to the subnival zone of the Sino-Himalaya

Previous phylogeographical studies of the Sino-Himalaya (SH) regions have mainly focused on seed plants from forest or alpine grassland habitats, whereas the flora of the subnival summits, especially the ferns, has largely been ignored. Here, we report on phylogeographical studies on Polystichum glaciale, a rare fern endemic to the subnival belt of the SH region. Based on cpDNA/nDNA sequences, strikingly rich genetic diversity was detected in P. glaciale. Combined with the lack of ‘isolation by distance’ and the major genetic differentiation among populations revealed by AMOVA, they collectively suggested that P. glaciale exhibited island-like population genetic structure. Phylogeographical structure with two genetic groups (N vs. S) was further identified in P. glaciale by the SAMOVA based on cpDNA data, of which the geographical pattern was mainly associated with the biogeographical boundary between the northern and southern Hengduan Mountains at 29°N latitude. We concluded that extremely complex topography of SH region and highly fragmented subnival habitat have played a critical role in shaping phylogeographical structure and genetic differentiation of P. glaciale. Mismatch distribution analyses and ecological niche modelling suggested P. glaciale has undergone north-westward retreat after the LGM. Predictions of its future distribution indicated the possibility of compression within suitable subnival habitats. We suggest in situ conservation should be urgently implemented to preserve this rare fern. Our results represent a first framework for a comprehensive understanding of the biogeographical history of fern species associated with the subnival belt of the SH region and the effects of historical events on its genetic architecture.