Regulation of the α-expansin gene OsEXPA8 expression affects root system architecture in transgenic rice plants

Expansins are cell wall proteins implicated in the control of plant growth via loosening of the extracellular matrix, and are encoded by a large gene family. However, data linked to loss of function of single genes which support the role of expansins in root growth remain limited. In this study, we used RNA interference to examine the biological functions of the rice α-expansin gene OsEXPA8. Repression of OsEXPA8 expression in rice impaired the root system architecture and plant growth significantly, leading to shorter primary roots and fewer lateral roots. Accordingly, the cell size of the root vascular bundle reduced drastically. Notably, OsEXPA8 silencing impaired root hair elongation; moreover, plant height was clearly reduced. Transient expression of OsEXPA8-GFP in onion epidermal cells verified that OsEXPA8 is located on the cell wall. OsEXPA8 was expressed predominantly in the root and shoot of one-week-old rice seedlings, and highly induced by NaCl but suppressed by nitrate and phosphate starvation. In addition, atomic force microscopy was used to explore alterations in cell wall nanomechanics caused by OsEXPA8 protein reduction, which showed that the wall stiffness (Young’s modulus) of OsEXPA8-silenced suspension cells was increased significantly. Taken together, our results suggest that OsEXPA8 is critical for root system architecture, which supports the hypothesis that expansins are involved in enhancing plant growth by mediating cell wall loosening.     

Modeling biophysical controls on canopy foliage water 18O enrichment in wheat and corn

Leaf water ¹⁸O enrichment is an important factor controlling the H₂¹⁸O, C¹⁸OO, and O¹⁸O exchanges between the biosphere and the atmosphere. At present, there is limited capacity to explain the enrichment mechanisms in field conditions. In this study, three models of varying complexity were used to simulate the leaf water ¹⁸O enrichment at the canopy scale. Comparisons were made among the models and with high‐frequency isotopic measurements of ecosystem water pools in wheat and corn. The results show that the steady state assumption was a better approximation for ecosystems with lower canopy resistance, that it is important to consider the effect of leaf water turnover in modeling the enrichment and not necessary to deal with time changes in leaf water content, and that the leaf‐scale Péclet effect was incompatible with the big‐leaf modeling framework for canopy‐air interactions. After turbulent diffusion has been accounted for in an apparent kinetic factor parameterization, the mean ¹⁸O composition of the canopy foliage water was a well‐behaved property predictable according to the principles established by leaf‐scale studies, despite substantial variations in the leaf water enrichment with leaf and canopy positions. In the online supplement we provided a discussion on the observed variability of leaf water ¹⁸O composition with leaf and canopy positions and on the procedure for correcting isotopic measurements for organic contamination.     

Evaluation of buccal cell collection protocols for genetic susceptibility studies

Buccal cells are increasingly used as a source of quality DNA to improve participation rates in molecular studies. Here, three buccal cell collection protocols were compared to determine factors affecting the yield of cells, total DNA per sample, and DNA yield per cell. In addition, kinetic quantitative polymerase chain reaction (PCR) (TaqMan™) was used to quantify human DNA available for PCR. The method of collection used influenced the overall DNA yield per sample. The collection buffer used influenced the number of cells but not the overall DNA yield per sample. Repeated freezing and thawing did not affect overall DNA yield per sample, DNA yield per cell, or the total number of cells collected. Mouthwashes had the highest DNA yield per sample (20.8 µg) compared with cytobrush samples (1.9 µg from three cytobrushes) and tongue depressors (0.8 µg from three tongue depressors). However, mouthwash samples may contain significant non-human DNA and other contaminants that could interfere with some molecular studies. Spectrometry grossly overestimated the total DNA recovered from mouthwash samples compared with fluorometry or quantitative PCR.     

Characterization of a novel cell wall-anchored protein with carboxylesterase activity required for virulence in Mycobacterium tuberculosis

Pooled mutant competition assays have shown that the Mycobacterium tuberculosis MT2282 gene (Rv2224c, annotated as encoding a proteinase) is required for bacterial survival in mice. To understand the mechanism of this requirement, we conducted a genetic and biochemical study of the MT2282 gene and its product. MT2282 encodes a member of the microbial esterase/lipase family with active site consensus sequences of G-X-S-X-G, and we have concluded that the MT2282 protein is, in fact, a cell wall-associated carboxylesterase rather than a proteinase, as initially annotated. The MT2282 gene product preferentially hydrolyzes ester bonds of substrates with intermediate carbon chain length. Purified MT2282 is a monomer with enzymatic catalysis properties that fit in the Michaelis-Menten kinetic model. Esterase activity was inhibited by paraoxon and dichlorvos. Replacement of Ser215, Asp450, and His477 by Ala in the consensus motifs completely abolishes esterase activity, suggesting that Ser215-Asp450-His477 forms a catalytic triad with Ser215 as an active site residue. To evaluate the role of the MT2282 in pathogenesis, the gene was deleted from the M. tuberculosis genome. BALB/c mouse aerosol infections showed reduced colony-forming unit loads in lungs and spleens and less lung pathology for the DeltaMT2282 mutant. High dose intravenous infection of mice with the mutant resulted in a significantly delayed time to death compared with the wild type or complemented mutant. These results indicate that MT2282 encodes a cell wall-associated carboxylesterase, which is required for full virulence of M. tuberculosis. We propose that MT2282 (Rv2224c) and its adjacent paralogous gene MT2281 (Rv2223c) be named caeA and caeB respectively, for carboxylesterase A and B.     

The use of stable isotopes to partition evapotranspiration fluxes into evaporation and transpiration

It is crucial to partition evapotranspiration (ET) into evaporation (E) and transpiration (T) components for better understanding eco-hydrological processes and their underlying mechanisms, and improving the establishment and validation of hydrological models at the ecosystem scale. Traditional eddy covariance technique serves as a useful tool to estimate ET, but it encounters difficulties in quantifying the relative contribution of E and T to ET. Combining with eddy covariance technique, it is possible to partition ET based on the measurements of stable oxygen and hydrogen isotopes in liquid and vapor phases of water in the Soil–Plant–Atmosphere Continuum (SPAC) system. The key challenge is to precisely determine the oxygen-18 and deuterium isotopic compositions of ET (δ_ET), E (δ_E) and T (δ_T). δ_E can be estimated based on the Craig–Gordon model. δ_T is usually approximated by the δ¹⁸O and δD of water in xylem or twig (δx), assuming δ_T equals δx under isotopic steady state (SSA). However, the SSA is only likely satisfied during midday in field conditions. The diurnal variations of δ_T is affected by isotopic composition of atmospheric water vapor (δ_v) and leaf water at the evaporating sites (δ_L,e), and relative humidity, resulting in the non-steady-state behavior of δ_T at the sub-daily cycles. δ_ET can be estimated using the flux-gradient approach or the Keeling plot by measuring the vapor mixing ratio and δ_v at different heights in the surface layer. However, δ_v observations by the traditional cold trap/mass spectrometer method are limited to a coarse time resolution, leading to discrete time series of δ_ET. It is now possible to make in situ and high time resolution measurements of δ_v and to analyze a large number of plant and soil samples due to technical and instrumental advances in recent years. It provides an opportunity to improve the model prediction of δ_L,e, and more importantly, to calculate δ_T from δ_L,e without invoking the SSA. Combining with the flux-gradient approach or the Keeling plot technique, continuous δ_ET measurements can be made. It offers us a premise for accurate ET partitioning on diurnal time scale. In this review we introduced the recent advances, foci and challenges for studies on ET partitioning using the stable isotopes technique.     

嗜热厌氧纤维素分解菌的分离、鉴定及其酶学特性

【目的】分离高效降解纤维素的嗜热厌氧菌,通过与嗜热产乙醇菌株联合培养的方式,为生产纤维素乙醇提供微生物资源。【方法】利用厌氧分离技术从降解纤维素的马粪富集物中分离到一株嗜热厌氧细菌HCp。采用形态学观察、生理生化鉴定、结合16S rDNA序列的系统发育学分析确定该菌株的分类地位,利用DNS酶活分析方法测定此分离菌株的酶学性质。【结果】分离菌株HCp革兰氏染色阴性,直杆,细胞单个或成对出现,菌体大小为(0.35-0.50)μm×(2.42-6.40)μm,严格厌氧,形成芽胞,能运动,对新霉素有一定的抗性。此菌能利用滤纸纤维素、纤维素粉、微晶纤维素、脱脂棉和水稻秸秆、明胶等,还可以利用葡萄糖、纤维二糖、木糖、木聚糖、果糖、蔗糖、核糖、半乳糖、麦芽糖、山梨糖、海藻糖、蜜二糖、甘露糖等。该菌株在pH6.5-8.5、温度35-70℃、盐浓度0%-1.0%范围内利用纤维素生长,最适pH为6.85,最适温度为60℃,最适NaCl浓度为0.2%,最佳生长条件下,在10 d内滤纸纤维素降解率可达90.40%。在HCp的纤维小体中,滤纸酶、羧甲基纤维素酶、β-葡萄糖苷酶、木聚糖酶的最适作用温度分别为70℃、70℃、70℃、60℃,并且羧甲基纤维素酶具有较高的热稳定性。部分长度的16S rDNA序列分析表明,分离菌株HCp与Acetivibrio cellulolyticus、A.cellulosolvens相似性为97.5%。【结论】分离菌株HCp是从马粪富集物中分离到的一株嗜热厌氧细菌,该菌具有较强的降解纤维素能力,生长温度范围广,酶的热稳定性好,纤维素底物利用广泛等特性,为纤维素降解产乙醇提供了良好的材料。     

Findings from the initial Stepwise Approach to Rabies Elimination (SARE) Assessment in China, 2019

In 2015, China and other member states of the United Nations adopted the goal of eliminating dog-mediated rabies by 2030. China has made substantial progress in reducing dog-mediated human rabies since peaking with more than 3,300 reported cases in 2007. To further improve coordination and planning, the Chinese Center for Disease Control and Prevention, in collaboration with the United States Centers for Disease Control and Prevention, conducted a Stepwise Approach towards Rabies Elimination (SARE) assessment in March 2019. Assessment goals included outlining progress and identifying activities critical for eliminating dog-mediated rabies. Participants representing national, provincial and local human and animal health sectors in China used the SARE assessment tool to answer 115 questions about the current dog-mediated rabies control and prevention programs in China. The established surveillance system for human rabies cases and availability of post-exposure prophylaxis were identified as strengths. Low dog vaccination coverage and limited laboratory confirmation of rabid dogs were identified gaps, resulting in an overall score of 1.5 on a scale of 0 to 5. Participants outlined steps to increase cross-sectoral information sharing, improve surveillance for dog rabies, increase dog vaccination coverage, and increase laboratory capacity to diagnose rabies at the provincial level. All assessment participants committed to strengthening cross-sector collaboration using a One Health approach to achieve dog-mediated human rabies elimination by 2030.     

厌氧微生物培养分离：过去、现在和未来

厌氧菌是地球上数量最多、物种最丰富的微生物,也是分类上报道最少的微生物。它们对氧气敏感、生长条件苛刻,不容易培养分离。本文简要总结了厌氧微生物的研究历史,分析了限制厌氧微生物培养分离的主要因素,讨论了厌氧微生物培养分离的策略和方法,回顾了国内外厌氧微生物的系统分类学现状,并展望了厌氧微生物培养分离的发展趋势。