转Bt水稻土壤跳虫群落组成及其数量变化

以转Bt水稻恢复系"克螟稻"(Cry1Ab纯合基因型)和"华恢1号"(Cry1Ab+Cry1Ac融合基因型)以及融合基因型转Bt水稻杂交系"Bt汕忧63",及其对照亲本水稻"秀水11"、"明恢63"和"汕优63"稻田土壤跳虫类群为对象,系统研究转Bt水稻种植下土壤跳虫群落组成及其数量动态变化,以评价不同基因型和不同育种品系转Bt水稻种植下稻田土壤生态安全性。结果表明,转Bt水稻种植导致土壤跳虫个别稀有类群的消失,并显著影响半土生和真土生类群以及土壤跳虫总量,但对群落多样性、均匀度和种类丰富度等影响不显著。与对照亲本相比,Cry1Ab转Bt稻田半土生类群和土壤跳虫总量及其种类丰富度指标显著增加了54.7%、44.4%和26.7%;Cry1Ab+Cry1Ac转Bt杂交稻田球角跳属百分比和真土生跳虫数量显著增加了212.3%和180.4%。就恢复系处理而言,与Cry1Ab转Bt水稻相比,Cry1Ab+Cry1Ac转Bt水稻种植导致棘跳属、球角跳属和原等跳属百分比以及半土生跳虫数量分别显著降低了62.1%、56.7%、61.8%和43.4%,同时,显著提高了裔符跳属百分比达88.2%。就Cry1Ab+Cry1Ac融合基因型转Bt水稻而言,与恢复系相比,转Bt杂交稻种植导致球角跳属和原等跳属百分比,半土生类群和土壤跳虫总量及其种类丰富度和群落多样性显著增加了312.9%和171.6%,302.4%和233.2%,以及54.0%和26.7%,同时,显著降低了裔符跳属百分比达65.5%。     

mTORC1-independent translation control in mammalian cells by methionine adenosyltransferase 2A and S-adenosylmethionine

Methionine adenosyltransferase (MAT) catalyzes the synthesis of S-adenosylmethionine (SAM). As the sole methyl-donor for methylation of DNA, RNA, and proteins, SAM levels affect gene expression by changing methylation patterns. Expression of MAT2A, the catalytic subunit of isozyme MAT2, is positively correlated with proliferation of cancer cells; however, how MAT2A promotes cell proliferation is largely unknown. Given that the protein synthesis is induced in proliferating cells and that RNA and protein components of translation machinery are methylated, we tested here whether MAT2 and SAM are coupled with protein synthesis. By measuring ongoing protein translation via puromycin labeling, we revealed that MAT2A depletion or chemical inhibition reduced protein synthesis in HeLa and Hepa1 cells. Furthermore, overexpression of MAT2A enhanced protein synthesis, indicating that SAM is limiting under normal culture conditions. In addition, MAT2 inhibition did not accompany reduction in mechanistic target of rapamycin complex 1 activity but nevertheless reduced polysome formation. Polysome-bound RNA sequencing revealed that MAT2 inhibition decreased translation efficiency of some fraction of mRNAs. MAT2A was also found to interact with the proteins involved in rRNA processing and ribosome biogenesis; depletion or inhibition of MAT2 reduced 18S rRNA processing. Finally, quantitative mass spectrometry revealed that some translation factors were dynamically methylated in response to the activity of MAT2A. These observations suggest that cells possess an mTOR-independent regulatory mechanism that tunes translation in response to the levels of SAM. Such a system may acclimate cells for survival when SAM synthesis is reduced, whereas it may support proliferation when SAM is sufficient.     

Cross-seeding of WT amyloid-β with Arctic but not Italian familial mutants accelerates fibril formation in Alzheimer's disease

Alzheimer’s disease (AD) involves the neurotoxic self-assembly of a 40 and 42 residue peptide, Amyloid-β (Aβ). Inherited early-onset AD can be caused by single point mutations within the Aβ sequence, including Arctic (E22G) and Italian (E22K) familial mutants. These mutations are heterozygous, resulting in an equal proportion of the WT and mutant Aβ isoform expression. It is therefore important to understand how these mixtures of Aβ isoforms interact with each other and influence the kinetics and morphology of their assembly into oligomers and fibrils. Using small amounts of nucleating fibril seeds, here, we systematically monitored the kinetics of fibril formation, comparing self-seeding with cross-seeding behavior of a range of isoform mixtures of Aβ42 and Aβ40. We confirm that Aβ40(WT) does not readily cross-seed Aβ42(WT) fibril formation. In contrast, fibril formation of Aβ40(Arctic) is hugely accelerated by Aβ42(WT) fibrils, causing an eight-fold reduction in the lag-time to fibrillization. We propose that cross-seeding between the more abundant Aβ40(Arctic) and Aβ42(WT) may be important for driving early-onset AD and will propagate fibril morphology as indicated by fibril twist periodicity. This kinetic behavior is not emulated by the Italian mutant, where minimal cross-seeding is observed. In addition, we studied the cross-seeding behavior of a C-terminal-amidated Aβ42 analog to probe the coulombic charge interplay between Glu22/Asp23/Lys28 and the C-terminal carboxylate. Overall, these studies highlight the role of cross-seeding between WT and mutant Aβ40/42 isoforms, which can impact the rate and structure of fibril assembly.     

The main driver of soil organic carbon differs greatly between topsoil and subsoil in a grazing steppe

Soil organic carbon (SOC) dynamics is regulated by a complex interplay of factors such as climate and potential anthropogenic activities. Livestocks play a key role in regulating the C cycle in grasslands. However, the interrelationship between SOC and these drivers remains unclear at different soil layers, and their potential relationships network have rarely been quantitatively assessed. Here, we completed a six‐year manipulation experiment of grazing exclusion (no grazing: NG) and increasing grazing intensity (light grazing: LG, medium grazing: MG, heavy grazing: HG). We tested light fraction organic carbon (LFOC) and heavy fraction organic carbon (HFOC) in 12 plots along grazing intensity in three soil layers (topsoil: 0–10 cm, mid‐soil: 10–30 cm, subsoil: 30–50 cm) to assess the drivers of SOC. Grazing significantly reduced SOC of the soil profile, but with significant depth and time dependencies. (1) SOC and SOC stability of the topsoil is primarily regulated by grazing duration (years). Specifically, grazing duration and grazing intensity increased the SOC lability of topsoil due to an increase in LFOC. (2) Grazing intensity was the major factor affecting the mid‐soil SOC dynamics, among which MG had significantly lower SOC than did NG. (3) Subsoil organic carbon dynamics were mainly regulated by climatic factors. The increase in mean annual temperature (MAT) may have promoted the turnover of LFOC to HFOC in the subsoil. Synthesis and applications. When evaluating the impacts of grazing on soil organic fraction, we need to consider the differences in sampling depth and the duration of grazing years. Our results highlight that the key factors influencing SOC dynamics differ among soil layers. Climatic and grazing factors have different roles in determining SOC in each soil layer.     

谷氨酸棒杆菌L-天冬氨酸α-脱羧酶在大肠杆菌中的表达及酶转化生产β-丙氨酸

【目的】克隆谷氨酸棒杆菌来源L-天冬氨酸α-脱羧酶基因, 实现其在大肠杆菌中的异源表达, 并进行酶转化L-天冬氨酸合成β-丙氨酸的研究。【方法】PCR扩增谷氨酸棒杆菌L-天冬氨酸α-脱羧酶基因pand, 构建表达载体pET24a(+)-Pand, 转化宿主菌大肠杆菌BL21(DE3), 对重组菌进行诱导表达, 表达产物经DEAE离子交换层析和G-75 分子筛层析纯化后进行酶学性质研究, 然后进行酶转化实验, 说明底物和产物对酶转化的影响。【结果】重组菌SDS-PAGE分析表明Pand表达量可达菌体总蛋白的50%以上, AccQ·Tag法检测酶活达到94.16 U/mL。该重组酶最适反应温度为55 °C, 在低于37 °C时保持较好的稳定性, 最适pH为6.0, 在pH 4.0?7.0范围内有较好的稳定性。酶转化实验说明: 底物L-天冬氨酸和产物β-丙氨酸对转化反应均有抑制作用; 实验建立了较优的酶转化反应方式, 在加酶量为每克天冬氨酸3 000 U时, 以分批加入固体底物L-天冬氨酸的形式, 使100 g/L底物转化率达到97.8%。【结论】重组L-天冬氨酸α-脱羧酶在大肠杆菌中获得高效表达, 研究了酶转化生产β-丙氨酸的影响因素, 为其工业应用奠定了基础。     

七叶一枝花种子萌发过程中内源激素含量及酶活性变化研究

为探究七叶一枝花的种子萌发生理机制,该文从种胚形态上对七叶一枝花种子萌发过程的时期进行了划分,并分析了不同时期种子内源激素含量及相关酶活性的变化规律。结果表明:(1)根据种胚形态可将种子萌发过程细分为8个时期,即种胚未萌动时期(S1期)、心形胚时期(S2期)、种胚膨大时期(S3期)、胚根未突破种皮时期(S4期)、子叶柄伸长和胚根突破种皮时期(S5期)、下胚轴突破种皮时期(S6期)、上胚轴伸长时期(S7期)、胚根伸长时期(S8期)。(2)不同萌发时期种子的α-淀粉酶活性均明显高于β-淀粉酶。(3)超氧化物歧化酶(SOD)活性在S5期最高,S1期最低; 过氧化物酶(POD)和过氧化氢酶(CAT)活性随种子萌发进程总体呈上升趋势,可溶性蛋白含量随种子萌发进程先下降后升高。(4)吲哚乙酸(IAA)、赤霉素(GA₃)、脱落酸(ABA)和水杨酸(SA)含量随种子萌发进程整体呈下降趋势; 1-氨基环丙烷羧酸(ACC)、茉莉酸(JA)、油菜素内酯(BRs)随种子萌发进程整体呈上升趋势; 细胞分裂素类(CTKs)含量无显著变化; IAA/ABA和GA₃/ABA随种子萌发进程呈先下降后上升趋势,而CTKs/ABA则不断升高。(5)ABA、IAA、GA₃含量与胚率呈负相关,而ACC、JA、BRs、POD、CAT、β-淀粉酶活性与胚率呈正相关。综上认为,七叶一枝花在不同时期种子内源激素含量及相关酶活性各不相同,其中α-淀粉酶活性、POD活性可能与种胚胚根伸长有关,GA₃可能影响种胚形成,而ABA则可能抑制种胚的生长发育。     

Fibroblasts rescue oral squamous cancer cell from metformin-induced apoptosis via alleviating metabolic disbalance and inhibiting AMPK pathway

Metformin is an antidiabetic drug widely used for the treatment of type 2 diabetes. Growing evidence suggests that it may exert antitumor effects in vivo and in vitro. However, even with the promising potency on defeating cancer cells, the pre-clinical and epidemiological studies of metformin on various kinds of cancers are not satisfactory, and the reasons and underlying mechanisms remain unknown. Since cancer is a complex system, dependent on a promoting microenvironment, we hypothesize that the interactions between cancer cells and their neighborhood fibroblasts are essential for metformin resistance. To test this, we used a cell co-culture model closely mimicking the in vivo interactions and metabolic exchanges between normal stromal cells (NOFs) and oral squamous cancer cells (OSCC). Here we show that while metformin can significantly inhibit cell growth and induce apoptosis of OSCC cultured alone in a dose-dependent manner through activating p-AMPK^T172 and modulating Bcl-2, Bax, and cleaved PARP. However, when OSCC are co-cultured with NOFs the metformin effects on OSCC cells are annihilated. NOFs are rescuing OSCC from metformin – induced apoptosis, at least partially, through inhibiting the activity of AMPK and PARP, maintaining mitochondrial membrane potential and increasing the oxidative stress. Our results indicate that metformin effects on oral cancer cells are modulated by the microenvironment and that this has to be taken into consideration in the context of developing a new combination of drugs for oral cancer treatment.     

硫酸盐还原菌对水解聚丙烯酰胺黏度的影响

目的:研究硫酸盐还原菌对油田驱油用水解聚丙烯酰胺体系黏度的影响.方法:以油田回注水配制不同分子量的HPAM溶液,考察硫酸盐还原菌在不同分子量聚合物中的生长繁殖情况及对HPAM溶液黏度的影响.结果:中分、高分、超高分HPAM-采出水体系初始黏度为21.7、25.4、38.9mPa·s.低于灭菌处理的23.0、27.8、45.8mPa·s.上述体系黏度在24h内明显下降.SRB的数量也由初始的3.0×103cfu/mL降低至10～102cfu/ml.结论:短期内SRB对高浓度的HPAM降解作用有限.SfUB培养物中的Fe2+是造成HPAM黏度下降的主要原因.SRB对HPAM黏度的影响是间接的.