PlpA,a PilZ‐like protein,regulates directed motility of the bacterium Myxococcus xanthus

The rod‐shaped bacterium Myxococcus xanthus moves on surfaces along its long cell axis and reverses its moving direction regularly. Current models propose that the asymmetric localization of a Ras‐like GTPase, MglA, to leading cell poles determines the moving direction of cells. However, cells are still motile in the mutants where MglA localizes symmetrically, suggesting the existence of additional regulators that control moving direction. In this study, we identified PlpA, a P ilZ‐l ike p rotein that regulates the direction of motility. PlpA and MglA localize into opposite asymmetric patterns. Deletion of the plpA gene abolishes the asymmetry of MglA localization, increases the frequency of cellular reversals and leads to severe defects in cell motility. By tracking the movements of single motor particles, we demonstrated that PlpA and MglA co‐regulated the direction of gliding motility through direct interactions with the gliding motor. PlpA inhibits the reversal of individual gliding motors while MglA promotes motor reversal. By counteracting MglA near lagging cell poles, PlpA reinforces the polarity axis of MglA and thus stabilizes the direction of motility.     

茉莉酸甲酯对马尾松萜类合成酶活性及其细胞化学定位的影响

马尾松(Pinus massoniana)是我国南方生态建设与造林用材的主要树种,为了揭示马尾松抗虫机理尤其是诱导抗虫性的分子机制,该研究以马尾松幼苗为材料,通过外源喷施茉利酸甲酯(Me JA),分析了处理与对照间植株针叶显微结构、萜类合成酶活性及其细胞化学定位的变化。结果表明:在0.2 mmol·L~(-1)Me JA处理下马尾松植株松针中萜类物质,尤其是单萜、二萜的相对含量增加,马尾松毛虫拒食性明显,诱导抗性增强。显微观测中,针叶叶肉细胞内树脂道分泌物增加,叶绿体数目减少,但叶绿体体积增大,叶绿体片层结构增加。Me JA处理4周后,针叶中萜类合成酶活性增加,通过电镜酶细胞化学观察,膜系统尤其是叶绿体膜上萜类合成酶活性定位明显增强。这说明Me JA诱导的马尾松诱导抗性可能与改变的叶绿体结构及绿色质体萜类合成酶活性密切相关。     

表观调控rDNA转录的研究进展

rDNA是控制细胞核糖体生物合成的串联重复基因,影响着整体蛋白质的翻译水平,与细胞生长代谢息息相关.由于rDNA序列具有多拷贝的重复特征,其转录除了受一般转录机制的调节外,还受多重表观调控机制的调节,精细调控着rDNA的转录状态.一般认为rDNA分为活跃和沉默两种状态,分别与活跃染色质标记和异染色质标记相关.近些年来,发现一种平衡态rDNA的存在,更加丰富了rDNA表观机制的研究.H3.3是一种H3组蛋白变体,是近些年来的研究热点,已有报道H3.3可能在分子伴侣HIRA的介导下整合进入活跃rDNA,然而沉默rDNA的维持是否也与H3.3的作用相关需要更多的探索.CTCF是rDNA重复单元间的绝缘子成分,与H3.3相关但并不清楚是否也调控着rDNA的转录.该综述讨论了几种调控rDNA表观状态的机制,并对可能参与该过程的新机制提出了设想.     

阿特拉津高灵敏酶联免疫吸附检测法的建立

目的：建立高灵敏度的阿特拉津酶联免疫吸附检测法。方法：将间接竞争ELISA进行条件优化以提高检测灵敏度,包括包被抗原与一抗的最佳工作浓度筛选、选择一抗的最佳稀释度对包被抗原进行细化筛选、不同有机溶剂对竞争结合反应的影响、酶标二抗稀释度筛选等。用建立的酶联免疫检测法检测实际样品,再与高效液相色谱法（HPLC）检测进行比较。结果：利用优化后条件建立了阿特拉津间接竞争ELISA检测曲线,标准曲线的相关系数R²=0.9958,相关性较好。另由此标准曲线可得LOD （最低检出限）为1.972 ng/ml。用于检测实际样品,回收率在80%-120%之间。当添加样品浓度为（0~6） ng/ml时,该法的检测灵敏度高于HPLC。结论：新建立的阿特拉津ELISA特异性好、精密度高,可代替大型仪器用于阿特拉津实际样品检测。     

Cloning,purification and characterization of novel Cu-containing nitrite reductase from the <Emphasis Type="Italic">Bacillus firmus</Emphasis> GY-49

Nitrite is generated from the nitrogen cycle and its accumulation is harmful to environment and it can be reduced to nitric oxid by nitrite reductase. A novel gene from Bacillus firmus GY-49 is identified as a nirK gene encoding Cu-containing nitrite reductase by genome sequence. The full-length protein included a putative signal peptide of 26 amino acids and shown 72.73% similarity with other Cu-containing nitrite reductase whose function was verified. The 993-bp fragment encoding the mature peptide of NirK was cloned into pET-28a (+) vector and overexpressed as an active protein of 36.41 kDa in the E.coli system. The purified enzyme was green in the oxidized state and displayed double gentle peaks at 456 and 608 nm. The specific activity of purified enzyme was 98.4 U/mg toward sodium nitrite around pH 6.5 and 35 °C. The K _m and K _cat of NirK on sodium nitrite were 0.27 mM and 0.36?×?10³ s^?1, respectively. Finally, homology model analysis of NirK indicated that the enzyme was a homotrimer structure and well conserved in Cu-binding sites for enzymatic functions. This is a first report for nitrite reductase from Bacillus firmus, which augment the acquaintance of nitrite reductase.     

Photosynthetic physiological performance and proteomic profiling of the oleaginous algae <Emphasis Type="Italic">Scenedesmus acuminatus</Emphasis> reveal the mechanism of lipid accumulation under low and high nitrogen supplies

In this study, we presented cellular morphological changes, time-resolved biochemical composition, photosynthetic performance and proteomic profiling to capture the photosynthetic physiological response of Scenedesmus acuminatus under low nitrogen (3.6 mM NaNO₃, N^?) and high nitrogen supplies (18.0 mM NaNO₃, N⁺). S. acuminatus cells showed extensive lipid accumulation (53.7% of dry weight) and were enriched in long-chain fatty acids (C16 & C18) under low nitrogen supply. The activity of PSII and photosynthetic rate decreases, whereas non-photochemical quenching and dark respiration rates were increased in the N^? group. In addition, the results indicated a redistribution of light excitation energy between PSII and PSI in S. acuminatus exists before lipid accumulation. The iTRAQ results showed that, under high nitrogen supply, protein abundance of the chlorophyll biosynthesis, the Calvin cycle and ribosomal proteins decreased in S. acuminatus. In contrast, proteins associated with the photosynthetic machinery, except for F-type ATPase, were increased in the N⁺ group (N⁺, 3 vs. 9 days and 3 days, N⁺ vs. N^?). Under low nitrogen supply, proteins involved in central carbon metabolism, fatty acid synthesis and branched-chain amino acid metabolism were increased, whereas the abundance of proteins of the photosynthetic machinery had decreased, with exception of PSI (N^?, 3 vs. 9 days and 9 days, N⁺ vs. N^?). Collectively, the current study has provided a basis for the metabolic engineering of S. acuminatus for biofuel production.     

Overexpression of the transcription factor MdbHLH33 increases cold tolerance of transgenic apple callus

As cold stress greatly affects plant growth and development, understanding the mechanisms underlying cold tolerance in plants is important. In this study, we analyzed the expression levels of apple (Malus domestica) MdbHLH33 and MdCBF1–5 by semi-quantitative PCR after exposure to 4 °C for different amounts of time and generated evolutionary trees for MdbHLH33 and the MdCBFs. Overexpressing MdbHLH33 pro-GUS in ‘Orin’ callus, indicated that transgenic callus had higher GUS activity and was more deeply stained at 4 °C than at 25 °C. Subcellular localization showed that MdbHLH33 was located in the nucleus. Overexpressing MdbHLH33 in ‘Orin’ callus increased the expression level of MdCBF2, MdCOR15A-1, and MdCOR15A-2, and resulted in increased cold tolerance. EMSA and Chip-PCR analysis showed that MdbHLH33 could bind the LTR cis-acting element found in the MdCBF2 promoter. Overexpressing MdCBF2 in ‘Orin’ callus indicated that MdCBF2 could also increase the expression level of MdCOR15A-1 and MdCOR15A-2 and improve cold tolerance; we also found that transgenic callus overexpressing MdCBF2 had reduced MdCBF1 and MdCBF5 expression and increased MdCBF3 and MdCBF4 expression. Overall, these results show that MdbHLH33 can regulate the expression of MdCBF2 and improve the cold tolerance of transgenic callus.     

Loss of alkaline ceramidase inhibits autophagy in Arabidopsis and plays an important role during environmental stress response

Sphingolipids, a class of bioactive lipids found in cell membranes, can modulate the biophysical properties of the membranes and play a critical role in signal transduction. Sphingolipids are involved in autophagy in humans and yeast, but their role in autophagy in plants is not well understood. In this study, we reported that the AtACER, an alkaline ceramidase that hydrolyses ceramide to long‐chain base (LCB), functions in autophagy process in Arabidopsis. Our empirical data showed that the loss of AtACER inhibited autophagy, and its overexpression promoted autophagy under nutrient, salinity, and oxidative stresses. Interestingly, nitrogen deprivation significantly affected the sphingolipid's profile in Arabidopsis thaliana, especially the LCBs. Furthermore, the exogenous application of LCBs also induced autophagy. Our findings revealed a novel function of AtACER, where it was found to involve in the autophagy process, thus, playing a crucial role in the maintenance of a dynamic loop between sphingolipids and autophagy for cellular homeostasis under various environmental stresses.